GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on September 19, 2022, 07:40:05 PM
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I have come up with a crazy idea for what may be my last big (and heavy) project.... My hands are getting very arthritic, and I don't know if I will be able to complete this one, but I have decided to have a go.... The concept is to use two 700 cc Carbon Fibre 4500 psi Bottles mounted under a plenum of equal length (16") made from 4130 CrMoly tubing of the same dimensions as an MRod tube.... ie 1.25" OD x 0.95" wall.... Here are the bottles, which I have on order from Wes at ArcheryAirgunFun in Saskatchewan.... https://airgunarcheryfun.ca/ (https://airgunarcheryfun.ca/)
(https://airgunarcheryfun.ca/wp-content/uploads/2021/12/700cc-alsafe2.png)
The two tanks will be mounted side by side with the plenum above, using a scaled up version of this tank block I made for two 88 gr. CO2 cylinders.... The three holes in the block will be threaded 18mm x 1.5mm, with the regulator screwing into the upper hole, and stubs made from 18mm steel bolts used to mount the tanks.... They will be sealed to the block with an O-ring at the parting face to the top of the tank....
(https://hosting.photobucket.com/albums/oo221/rsterne/QB on HPA/.highres/Threaded and O_rings_zpsojaggrh9.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/albums/oo221/rsterne/QB on HPA/.highres/Threaded and O_rings_zpsojaggrh9.jpg?width=1920&height=1080&fit=bounds)
There will be a short piece of Picatinny rail mounted on the bottom of the block to mount a BiPod, like I did on the converted QB....
(https://hosting.photobucket.com/albums/oo221/rsterne/QB on HPA/.highres/Picatinny and Barrel Band_zpsuaasfgwo.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/albums/oo221/rsterne/QB on HPA/.highres/Picatinny and Barrel Band_zpsuaasfgwo.jpg?width=1920&height=1080&fit=bounds)
Here is a sketch of how I plan to mount an adjustable Ninja Regulator, with the bonnet inside the end of the plenum tube.... The adapter is shown in red....
(https://hosting.photobucket.com/images/oo221/rsterne/Ninja_Adapter(1).jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/Ninja_Adapter(1).jpg?width=1920&height=1080&fit=bounds)
I will turn down the OD of the bonnet by 0.020" for a length of 1/2", and that part will fit inside the end of the tube.... The bonnet setscrews will be accessible without removing the bonnet from the tube if a regulator rebuild is necessary.... Since the adapter is mounted with four 10-32 screws into the tube, the assembly can be turned in 90 degree increments for orientation of the regulator, and then the position fine tuned by rotating it on the 1/2" NPS bonnet threads, and then the position locked into place with two setscrews.... Here is what the dual tank CO2 setup looked like to give you an idea of the plan....
(https://hosting.photobucket.com/albums/oo221/rsterne/QB on HPA/.highres/Twin Tanks_zpsvz03pf0o.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/albums/oo221/rsterne/QB on HPA/.highres/Twin Tanks_zpsvz03pf0o.jpg?width=1920&height=1080&fit=bounds)
I have not made a final decision yet on caliber, but if Al at NOE makes the mold I have asked for, this Lothar Walther barrel is what I would use....
https://www.lothar-walther.com/gun-barrel-blanks/rifle-barrels/standard-european/1079/barrel-blank-twist-5.9-4-6x30mm-od-1.26-l-26.18-cr-moly-steel?c=34 (https://www.lothar-walther.com/gun-barrel-blanks/rifle-barrels/standard-european/1079/barrel-blank-twist-5.9-4-6x30mm-od-1.26-l-26.18-cr-moly-steel?c=34)
(https://hosting.photobucket.com/images/oo221/rsterne/Barrel.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/Barrel.jpg?width=1920&height=1080&fit=bounds)
(https://hosting.photobucket.com/images/oo221/rsterne/Barrel_Specs.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/Barrel_Specs.jpg?width=1920&height=1080&fit=bounds)
I haven't decided whether to use this profile, or something a bit lighter....
(https://hosting.photobucket.com/images/oo221/rsterne/Proflie.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/Proflie.jpg?width=1920&height=1080&fit=bounds)
Here is a drawing of the bullet I have asked Al to make a mold for.... It is a full 4 calibers long, and made for the 5.9" twist of the 4.6mm barrel from LW....
(https://hosting.photobucket.com/images/oo221/rsterne/N.O.E._Bullet_Moulds_183-39-RN_BT_R6_Sketch.Jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/N.O.E._Bullet_Moulds_183-39-RN_BT_R6_Sketch.Jpg?width=1920&height=1080&fit=bounds)
This is very much a matter of finding the fastest twist barrel I could afford in a small caliber, and building the bullet and gun around it.... It will take about 3000 psi to get into the 900's and the plenum is good for the full 4500 psi at a 3.5:1 safety margin.... There will be 1.4 litres of air (85 CI), so if I can achieve an efficiency of 1.0 FPE/CI, at 85 FPE I should get about 70 shots with a 1000 psi (70 bar) drop in tank pressure.... I hope it all comes together.... 8)
Bob
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Sounds like fun Bob. I really like the double block. I have a 30 cal armada I wouldn't mind double tanking.
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I think it’ll come together just fine. For sure will be interesting. Look forward to progress updates.
Dave
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Following!
Time to start those winter projects for folks up north. Too cold to do anything outside. Here in central Fl, it'll be cool enough to work in the garage for more than a couple of hours each morning. :o ;D
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Pending finding a regulator that can handle outputs of 2800-3600 psi that will fit and I can afford.... and considering the costs.... this project is unfortunately on hold for now.... :(
Bob
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What about the pcp only one ninja makes? It has a steel output thread and I think a smaller diameter on the high side of piston. I can check that if you want me to.
It comes set at 3000 but I’m sure you could change Belleville stack.
Dave
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There are 3000psi regulators available. 3000psi is a good set point for a high energy airgun.
Adding a couple inches of barrel length could get you the same fpe potential as adding a couple hundred psi.
It’s an interesting project. 1400cc on a .177 bench - that’s a lot of shots.
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I have been looking at the numbers, and I think I will need more than 3000 psi to get into the 1000's.... The barrel is only available in one length, 26".... I don't know if the high pressure Ninja can go to 3600-3700, but I think 3000 is about the minimum usable with such a high SD slug (0.166) with a 26" barrel....
Bob
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I put the design into my spreadsheet and got these results:
3000psi set pressure
215cc plenum
0.18 caliber with full diameter ports
1400cc tank filled to 4000psi
stock Cothran Powerhouse Marauder valve
26" barrel
assume a SSG type or solenoid activated hammer, very light, giving a 0.0025 sec dwell
39gr slug
1028fps 91fpe
73 shots per fill
The spreadsheet results are usually fairly close to actual results, so you should be able to get pretty close to 1000fps.
For maximum FPE with the 26" barrel at 3000psi set point, if you could extend the dwell to 0.0035 (anymore and you risk blasting out lots of excess air without any gain):
1090fps 103fpe
43 shots/fill
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I just checked the regulator. I can get it set to approx 3900 by adding 1 Belleville to the stack. That’s pretty close to max I feel like.
The only thing about these regs are they are normally only found in 5/8-18. Hmm, just a thought, maybe the bodies are the same as normal regs, I’ll have to check that.
Anyway, so yes, you can run the pressure up on them.
Dave
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If I input the data from my .172 cal at 2800 psi (165 cc plenum) with a 28" barrel, where I get 1050 fps with a 24.5 gr. slug with an efficiency of 0.96 FPE/CI, using a dwell of 0.00243 sec.... Lloyd's spreadsheet says the overall efficiency is just 79%.... If I then change to .183 cal and 39 gr., increase the plenum to 215 cc at 3000 psi, with a 26" barrel, using a dwell of 0.0025 sec. and staying with the 79% efficiency, I get only 923 fps (74 FPE) with an efficiency of 1.12 FPE/CI.... It would require an increase in efficiency to 90%, and a dwell of 0.0027 sec. to get your predicted velocity and shot count.... I think that is extremely unlikely.... If I drop the efficiency down to 80% (I think much more likely), leaving the dwell at 0.0025 sec. I then get 1020 fps (90 FPE) at 0.98 FPE/CI.... Increasing the dwell to 0.0035 sec. (valve closing at the muzzle), I get 1070 fps (99 FPE), but the efficiency drops to 0.61 FPE/CI.... I think basing these numbers off an existing .172 cal gun I already have should be closer to reality, so I would not count on being able to use much less than 3600 psi or so to get into the mid-1000's....
Bob
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Hey, Dave.... That's really good information, many thanks for testing it for me.... What are the diameters of the ends of the piston (where the O-rings are)?.... Actually the ID of the bores would be the most accurate information.... Using the original 10 x 0.032" Bellevilles and shimming them would give a wonderful range of adjustment (actually should be able to get to about 4300 psi before they go flat, 10 Bellevilles have a higher spring rate than do 11, with the same maximum force).... The threads are not an issue, I can thread the top of the tank block whatever I want.... However, I would have to drain and disassemble the gun to adjust the regulator by shimming.... Not a complete deal breaker, but I was hoping to use the adjustable Ninja, with the wheel for external adjustment.... I wonder if they use the smaller diameter piston?....
Bob
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The one I got from haji (flex) had the larger size piston head. It was set up for 3000 max by him. I have another set up from ninja (flex) that is a small bottle thread and 3000 max, I can check it.
Next time I’m in the shop I’ll get some more info for you.
Dave
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Bob,
You said:
"overall efficiency is just 79%"
"It would require an increase in efficiency to 90%"
What does the efficiency represent? Projectile fpe/???
The custom set point regulators that Hajimoto sells have M18x1.5 tank threads, and a steel bonnet.
https://hajimotoproductions.com/index.php/product/ninja-high-pressure-metric-m18-custom-output/
The Ninja-flex reg has an aluminum bonnet (at least mine does).
Except for the Flex, Ninja PCP regs with a 3000psi output rating have steel bonnets. At least the ones that I have encountered.
I have found that the custom regs seem to provide a more consistent pressure. I'll sometimes use the Flex reg to decide on a pressure setting, and once decided, then switch it out for a fixed pressure reg.
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I thought you would remember, the "efficiency" in Lloyd's spreadsheet is a "fudge factor" to make the actual performance of the gun match the spreadsheet numbers.... Once you input the known data, there is only ONE combination of dwell and "efficiency" that will give BOTH the FPE and FPE/CI numbers you got with your gun.... Generally, the fudge factor that works for one gun is correct for a very similar one when you are trying to make a prediction.... His spreadsheet includes (or can ignore) the mass of air used, and a few other losses (transfer port volume, an estimate of bullet starting and sliding forces, etc.), but yes, it would be how much of a percentage of the "remaining theoretical FPE" (once those factors are included) ends up in the projectile.... Typical values are 75-85%, and occasionally higher or lower....
Thanks for the info about the regs....
Bob
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Large side piston (cylinder actually) .390”
Small side cylinder .319”
This is on the fixed output 3000psi steel bonnet
I was mistaken on my ninja set flex, it’s a 1700-2200, not a 3000.
It has the same small side piston and the large end cylinder is .549”
Hope that helps.
Dave
Flex on the left, obviously
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OK. I do it a little different. I do 100% accounting for energy:
energy in = energy out
potential energy of air used = slug FPE + sliding friction(heat) + KE of air + remaining potential energy of air
I've been using very long barrels, so getting the desired FPE mostly becomes a function of adequate dwell. I guess my fudge factor is the dwell. Underestimated dwell would throw off my shot count. The best way for me to account for efficiency would be:
(actual shot count)/(expected shot count)
With a big tank volume, shot count is rarely an issue. OK, I now seem to remember us having this conversation before.
I still think with 3000psi, you can get the 1020fps with sufficient dwell (probably not the 1090fps). After EBR, I'll play with the Cothran valve dwell and see if I'm really off.
What kind of valve do you plan on using?
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I was planning on making my own balanced valve, with a change or two to incorporate what we all have learned about them over the past couple of years.... Full size porting goes without saying, and I use a retractable bolt probe that is adjustable so that I can occlude the barrel port to reduce power if required.... The combination of optimizing the SSG hammer for the pressure used, to get decent efficiency and a low ES, and then the ability to choke down the flow to the bullet is a good one that I have used successfully for several years now....
I have been thinking about what you were saying about using a Flex and then changing to the HP Ninja for increased stability, and that sounds great if you are working with under 3000 psi (within the range of the Flex).... I can do something similar to determine the setpoint of the regulator by using a "tiny tank" on the regulator input and tethering it to my SCBA while experimenting with the pressure.... I did that with my 6mm.... Click on the pic to enlarge....
(https://hosting.photobucket.com/albums/oo221/rsterne/6mm Sporter/.highres/Regulated for Testing_zpsozzbopsf.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/albums/oo221/rsterne/6mm Sporter/.highres/Regulated for Testing_zpsozzbopsf.jpg?width=1920&height=1080&fit=bounds)
I have two of the tiny tanks for regulator testing, one 5/8"-18 and the other 18x1.5 mm.... They only have a volume of a few ccs.... In that photo I have a digital gauge on the regulator inlet, and I can feed that with a tether for continuous shooting (at whatever the reg. setpoint is) or I can shut off the SCBA tank and bleed the line to determine the pressure in the plenum (block and tiny tank included) for one shot....
The new gun would be the same basic design as the 6mm above, but the regulator would be inline with the plenum, attached to the top of the "Y" block holding the two bottles....
The reason I was a bit confused on the Ninja HP regulator is that I have one here, that says 2200 psi on it, and "not for paintball", and it looks just like yours, Dave.... However, the piston is the old 0.55" diameter one, and to get 2200 psi it has four sets of triple 0.032" Bellevilles and some thin shims.... They are arranged.... ))) ((( ))) (((
I have a spreadsheet that calculates the force needed from the Bellevilles for any given pressure output for the 0.55" piston regs.... I copied it and changed the large end to 0.390", and then looked at what the setpoint might be with 10 and 11 Bellevilles that are 0.032" thick (with no shims).... I got the following, assuming that the space available for the Bellevilles (0.430") is the same as the regs. with the larger pistion:
10 x 0.032" (no shims) = 2150 psi @ 91 lbf..... and varying by 43 psi per thou, with room for 0.110" of shims....
11 x 0.032" (no shims) = 3800 psi @ 161 lbf..... and varying by 39 psi per thou, with room for 0.078" of shims....
In both cases, there is room for more shims than required to drive the 0.032" Bellevilles completely flat, which requires 260 lbf.... That would give a setpoint of way over 4500 psi, so that means that if the room for the Bellevilles is still 0.430", the stack of 10 x 0.032" should be adjustable from 2200 psi to tank pressure, and with 11 x 0.032" from 3800 to tank pressure.... If these assumptions and calculations are correct, that stack of 10 x 0.032" is perfect for the Ninja HP reg.... A 0.030" shim should give about 3400-3500 psi....
Bob
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Watching with interest, that many shots at that FPE will be a beastly build! 8)
Jesse
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Just for information purposes Bob. I had an idea on my flex that seems to work.
I made a piston with a smaller dominant head and a sleeve for the bonnet. The sleeve is held in place by a steel washer. It makes the bonnet set up just a tad higher but doesn’t cause any issues.
The Belleville stack is set up as singles now and appears to work as intended.
Dave
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.
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Pretty kewl!.... Would it be possible to use the steel bonnet from the HP reg. and make a piston to suit for the Flex?....
Bob
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It should, I was gonna try but I’ve got the hp aired up for shooting tomorrow.
Dave
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By special request, Hajimoto has agreed to make me a Flex (adjustable) Ninja Regulator with a steel bonnet, set up for a maximum of 3600 psi.... Ninja won't verify that it is OK, but the body and steel bonnet are both rated at 4500 psi MSWP.... I did the math for the CGA 320 threads on the adapter.... and I can use 2024-T3, but will use 7075-T6 for even more strength....
Al has confirmed that he will be making the mold for the .183 cal. 39 gr. bullet (eventually), so I just have to confirm I can get the barrel into Canada....
Bob
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By special request, Hajimoto has agreed to make me a Flex (adjustable) Ninja Regulator with a steel bonnet, set up for a maximum of 3600 psi....
I have never opened up my steel bonnet Hajimoto HP regs, so I don’t know what piston size is used. Do you know if your special request Flex will have a large or small piston?
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Pretty kewl!.... Would it be possible to use the steel bonnet from the HP reg. and make a piston to suit for the Flex?....
Bob
Sounds like Haji is going to get you fixed up. Between shooting today, I swapped the steel bonnet onto my flex, using the piston I made. Works fine. I left the bonnet backed off just a bit because my piston is a little long (to compensate for the washer I used in the flex bonnet).
Dave
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Scott, I don't think they make the Flex with a small piston, I will ask Haji....
Dave, thanks for that info.... How much range of adjustment do you have on the Flex with small piston?....
Bob
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Scott, I don't think they make the Flex with a small piston, I will ask Haji....
...
Bob
OK. But do they make a steel bonnet with a large piston? I would think the smaller diameter piston would be better for an HP output reg.
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I have a steel bonnet with the large piston, in fact a couple of them, so yes, they do (or at least did) make them.... He said he could supply a Flex with a steel bonnet, and I have asked him if it takes the large or small piston (hoping for the small)....
The basic difference between the large and small, when used at 3000 psi, is that the large piston requires 0.032" Bellevilles in four sets of three (108 psi/thou), whereas the small piston uses ten x 0.032" as singles (43 psi/thou).... This means with the small piston, there is much more travel, and a far softer spring rate, and so it should open further (and refill quicker) for a given pressure drop in the plenum....
Bob
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Bob,
I didn’t check max and min.
I do know where I had it set when airing it up was ~3200 and I adjusted from there to 3950. I have more adjustment left.
Dave
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My tanks have arrived from AirgunArchery Fun in Saskatchewan....
(https://hosting.photobucket.com/images/oo221/rsterne/700_cc_Tanks(1).JPG?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/700_cc_Tanks(1).JPG?width=1920&height=1080&fit=bounds)
They are gorgeous, and I love the long slender profile.... 8)
I have ordered the 4130 CrMoly tubing for the main tube, and some 2024-T3 for internal parts....
Bob
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What a great project!
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It turns out that I will also be getting a .22 cal LW pellet barrel with a VERY slow twist, compliments of Mike Niksch of Thomas Benchrest Rifles.... I helped Mike decide what to get for shooting 25.4 gr. JSB Monsters at 100 yards (he is trying to beat rimfires) and it is working well, so he is sending one as a thank you!.... Here is a 25 shot group he shot at 100 yards (looked like he pulled one).... :o
(https://hosting.photobucket.com/images/oo221/rsterne/25_shots_100_yards.JPG?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/25_shots_100_yards.JPG?width=1920&height=1080&fit=bounds)
I decided I will make up an upper to either fit on this gun, or since I have a pair of SIG 450 cc, 250 bar bottles, I might make another lower for it.... In any case, I borrowed the concept from my Monocoque .257 and came up with this unique way of marrying the barrel and breech....
(https://hosting.photobucket.com/images/oo221/rsterne/22_Benchrest_Barrel_Breech.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/22_Benchrest_Barrel_Breech.jpg?width=1920&height=1080&fit=bounds)
I have a meter long piece of 16mm ID CF tube (to fit the LW barrel) with a 20mm OD, and I have ordered a piece of 5mm wall CF tubing a meter long, 20mm ID x 30mm OD, to slide both it and the breech into.... Barrel in green, breech in blue, bolt in red above.... The breech will be 20mm OD, turned from 2024-T3, and sealed to the barrel with an O-ring.... The resulting assembly should be about the same stiffness as a 1-1/8" OD steel barrel, at a fraction of the weight....
Sidetracked, maybe, but this should be fun!.... ;)
Bob
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Excellent barrel! It should be a relief going into a build not wondering if your barrel is gonna be a shooter or just ho hum.
Can’t wait to see some build pictures.
Dave
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I have been thinking about a change to my balanced valve for this gun.... Here is a drawing, although the dimensions show a 5/16" throat (from my 6mm), which I can reduce to 1/4" for these smaller calibers, and reduce all the other dimensions proportionally if desired.... That would make the valve easier to open.... The balance chamber is 50% of the area of the poppet seat.... reducing the force required to crack the valve by that much....
(https://hosting.photobucket.com/images/oo221/rsterne/New_Valve.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/New_Valve.jpg?width=1920&height=1080&fit=bounds)
The valve body is in black, the poppet and front spider are in blue, the balance chamber is in red, and the O-rings in magenta.... The valve spring (green) is outside the balance chamber instead of inside it.... This allows the chamber to be much shorter, and therefore a lot less volume.... The balancing force is basically only going to reduce the force holding the poppet closed.... Once it opens 1/3rd of it's diameter (it may never get that far), the poppet (actually the buffer O-ring on it) hits the end of the balance chamber, which can slide 1/8" forward, driven by the momentum of the hammer.... As the balance chamber fills with HPA from the valve throat through the vent in the poppet stem, the closing force increases.... This allows the dwell to be tuned with the hammer strike....
If I need a larger balance chamber, I can move the balance chamber forward by tightening the screw that holds it in place in the spider.... That would reduce the hammer strike required as the valve would have a longer "blow open" period.... The balance chamber dimensions can be changed if a larger alteration in operation is needed....
Bob
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That’s gonna allow A LOT of tuning ability over a set amount of blow open. And I believe it to be easier on spiders.
Dave
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I just received my Carbon Fibre barrel sleeve from Amazon.ca....
(https://hosting.photobucket.com/images/oo221/rsterne/20_x_30_mm_CF_Tube.JPG?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/20_x_30_mm_CF_Tube.JPG?width=1920&height=1080&fit=bounds)
30mm (1.18") OD x 20mm ID, shown with my normal 20mm OD barrel sleeve inside it!....
(https://hosting.photobucket.com/images/oo221/rsterne/20_x_30_mm_CF_Tube_Wall.JPG?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/20_x_30_mm_CF_Tube_Wall.JPG?width=1920&height=1080&fit=bounds)
Anybody need a metre long CF Crowbar?.... ::)
Bob
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I have a question for those who have made successful benchrest rifles.... I am not talking about a "lead sled" mounted in it's own recoil carriage like the PB guys use with 6mm.... I am talking about a gun to be shot from bags, bipod or a forward rest, sitting on a bag against your shoulder (legal for NUAH rules, EBR, etc.etc.).... I know I can make a virtually rigid upper including the scope mount, something that will keep the barrel extremely well aligned, and immune from harmonics, relative to the scope.... How rigid does the attachment to the lower, which contains the valve, trigger, bipod mount and stock need to be?....
For example, could you use multiple barrel bands (eg. 2 or 3) to fasten them together? I'm talking about beefy ones that would rigidly clamp the two tubes together, at the rear, near the valve transfer port, and maybe another one further forward, possibly at the front tank block.... I guess what I am really asking is could you replace a bulky, hard to machine receiver, with a couple of clamps?.... Your thoughts?....
Bob
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Bob,
A one piece receiver should be stiffer and more robust against abuse than a modular one, but that depends on the stiffness of each part, and the integrity of each junction. As always, the devil is in the details.
Also, as you are not going to attach a bayonet and joust with this air rifle, "less robust" may not matter. Just don't use it as a crowbar.
The modular design of the RTI in the video below may serve as inspiration:
https://youtu.be/Euppxj2X5Rc
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If you need more inspiration, consider that aircraft fuselages and wings are made from flexible, light weight parts, that are fixtured into position and riveted together, to form precisely shaped robust parts.
As you would not be making many air rifles, the fixturing aspect would not be required, but there would be more consideration of the placement and alignment of parts during assembly.
If the pressure in the air tank was kept in a narrow range (tethered bench gun), then the variation in air tank swell and stretched length is unlikely to spring the barrel and cause the POI to drift during a session, or between sessions. You could even do the final torqueing of some barrel band screws after pressurizing the air tank, so there is no stress between tank and barrel at normal operating pressure.
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Thanks for those thoughts.... much appreciated....
Bob
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Bob,
That sort of thinking comes easily to me. I had pause before posting, because I am not qualified, being that I do not own, nor have I made a bench gun of any configuration.
I find that thinking in analogies often helps with perspective. I was granted an honorary blackbelt in analogies by a Swede once :)
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I have built a couple bench rest powder burners. Not used in competition but both turned out extremely accurate.
A couple of things I made sure in both builds
1. Free float barrel. No bands.
2. Rigidity from chamber area to BOTH bags.
One I made a long clamp top that secured barrel to chassis (stock) with eight machine screws. The bolt action floats within the chassis.
The objective is to have the effect recoil has on the shot be as consistent as possible.
Bipods are not the best in this case. A front bag that the stock can easily slide on and the stock can be placed the same before each shot.
If the buttstock is to be on a bag, the lower portion of stock needs to be parallel to barrel/forestock.
Just some suggestions Bob. You have a sketch of your general layout you have in mind? I like the idea of an easy to machine receiver. I think it can definitely be done and still be somewhat modular.
Dave
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I have decided to use bags instead of a BiPod, and the bottom of the stock will be about 6" long and parallel with the barrel.... It will likely be a 2x4 on edge, screwed to a tube that slides over the extended back end of the plenum tube, so adjustable in length and clamped to it for rigidity.... At the front, the twin bottles will supply a foot long, wide base, parallel to the barrel.... The front bag will have to sit on a wooden block to raise it up to the correct elevation.... No meaningful drawings yet, but the basis for the general arrangement is my 6mm regulated bottle gun....
(https://hosting.photobucket.com/albums/oo221/rsterne/6mm Sporter/.highres/6mm Sporter_zpsoihmeiqp.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/albums/oo221/rsterne/6mm Sporter/.highres/6mm Sporter_zpsoihmeiqp.jpg?width=1920&height=1080&fit=bounds)
Two 700 cc bottles will replace the single 500 cc, same PRod trigger group, flat bottom stock as described above....
Bob
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Bob,
It looks light an minimalistic. Thus attractive or scary, depending on perspective. I like it; but you should look at the weight of the parts and how bending moments are created and resisted. That should provide peace of mind or warn based on your expectations for rigidity in normal use.
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Well, the .183 cal barrel weighs about 7 lbs, and the plenum/valve/hammer tube is CrMoly, so also heavy.... Benchrest only, probably 15 lbs. total?....
The .22 pellet version will be MUCH lighter, carbon sleeved LW barrel, aluminum tube, two 450 cc bottles instead of two 700cc.... Similar to that drawing, except the breech / bolt assembly will be inside the 30mm OD barrel sleeve....
In both cases, the scope will be mounted on the barrel.... ;)
Bob
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Well, I'm still collecting bits and pieces for the new guns.... The barrels are on order, I'm getting a couple of Crosman PRod pistol trigger assemblies from Lloyd Sikes along with some tubing, and I gave my wife a big hint for a new 8-32 x 50 Scope for the .183 cal. for Christmas.... I have a Hawke 6-18 x 44 I took off my Hatsan for the .22 cal pellet barrel.... I have some more 6" long Picatinny rails coming, and my son has done up some tank spacer blocks with his 3D printer.... I got a new Ninja/Umarex regulator from Hajimoto, set to 3600 psi for the .183 cal, and I have a 2200 psi Ninja regulator for the .22 cal.... These will mount between the "Inverted Y" block that holds the two tanks and the front of the plenum/main tube.... The benchrest rear stocks will be a simple 2x4 attached to the bottom of piece of PVC pipe, slid over the main tube.... The bottom will be parallel to the barrel so that it will slide straight back on the rear bag during recoil....
Anyways, I haven't made any chips yet, but I'm getting closer.... ::)
Bob
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I was looking at different designs for an adjustable rail to allow setting the scope on a downslope to the barrel, to allow shooting out to at least 500 yards.... I found one called the Eratac (patent pending) that uses an asymmetric octagon to change the height of the back of the scope rail....
https://youtu.be/XAalf49foi4
It only has a total of 70 MOA of adjustment, and I needed about twice that, so I came up with a linkage to do that....
(https://hosting.photobucket.com/images/oo221/rsterne/Octagon_Cam_Adjuster.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/Octagon_Cam_Adjuster.jpg?width=1920&height=1080&fit=bounds)
As you turn the adjusting wheel (black) clockwise, each time it engages a new flat on the blue cam, it raises the back end of the red bar by 0.020".... Since the distance between the center of the cam and the pivot is (3600 / 1.047 / 1000) = 3.439", each thou changes the angle by 1 MOA, so each step changes it by 20 MOA.... There are 7 steps (140 MOA), and I intend to machine 20 MOA of angle into the bottom of the base that bolts to the barrel (which sights the gun at about 100 yards), so that gives me a total of 160 MOA available, which should be plenty to allow shooting at a target at over 500 yards away with pretty much any decent slug, starting at a MV of 900 fps or higher....
Bob
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Interesting concept, looks like it can be solidly locked once the adjustment is made.
Dave
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Yes, there are two screws, one on each pivot, that I assume pull the movable rail over against the fixed one when tightened.... The trick is to make to whole thing low enough that the scope isnt waayyy higher than required to clear the barrel when the objective tips downward.... ::) .... I'm guessing that is why the Eratac has the rings machined as part of the movable section of the mount.... ;)
Bob
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But still high enough your not looking at the muzzle, lol.
That is pretty nice the rings are built in. Just makes things that more solid.
Can’t wait to see some chips made!
Dave
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Simple, clever scope jack.
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I got three tank spacer wedges for my Dual Tank Benchrest guns today from my son.... He used his 3D printer....
(https://hosting.photobucket.com/images/oo221/rsterne/3D_Printed_Tank_Spacer.JPG?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/3D_Printed_Tank_Spacer.JPG?width=1920&height=1080&fit=bounds)
(https://hosting.photobucket.com/images/oo221/rsterne/Sample_Fitting.JPG?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/Sample_Fitting.JPG?width=1920&height=1080&fit=bounds)
They are 100% infill, so solid as a rock, easily capable of taking the compression from a hose clamp, which is what will hold the tanks rigid at the back.... This was a perfect solution, I'm sold on 3D printing for certain jobs such as this....
Bob
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That should work !!
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Simple and effective.
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I've sometimes wondered why we use barrel bands instead of hose clamps and filler wedges/pieces, probably because barrel bands look cooler.
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Yep, that would be my guess.... However, in this case it would be huge and hard to make, so a worm-drive hose clamp will be just fine!.... also much thinner!.... 8)
Bob
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Yep, that would be my guess.... However, in this case it would be huge and hard to make, so a worm-drive hose clamp will be just fine!.... also much thinner!.... 8)
Bob
Yes, I have used metal band with screw and nut to tighten it and spacer in between barrel and airtube without issues. Easy to make and shims can be added if needed. I eventually made a one piece band for that gun but IMO it's not really needed in most cases.
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Just to make you jealous, here is a Google Earth view of one of the locations I have permission to shoot ground squirrels and marmots on, just 10 km. away....
(https://hosting.photobucket.com/images/oo221/rsterne/Thomas_Ranch.jpg?width=undefined&height=undefined&fit=bounds) (https://hosting.photobucket.com/images/oo221/rsterne/Thomas_Ranch.jpg?width=1920&height=1080&fit=bounds)
The two red lines are 500 and 1000 yards long, so running out of range for testing airguns is not an issue.... 8)
Bob
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Wow! Almost looks like a golf course! You'll have to start a NUAT club. ;D
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But still high enough your not looking at the muzzle, lol.
sb327.... I checked the scope I have coming, and at the lowest magnification (8X) the field of view just touches the top of the muzzle when the scope is at maximum elevation (160 MOA).... so I think I should be OK.... The bell of the scope will clear the barrel by just over 1/8" as well.... I am waiting for the scope to arrive to double check everything, and I have some more aluminum bar stock coming as well.... Getting closer to making chips.... 8)
Bob
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Well, after months of collecting parts (I still haven't received the barrels, but LW has them on order), I finally got back into my shop to do some work on this project.... The shop needed a thorough cleaning (3 years of dust and debris) but it was sure nice to be working on an airgun again.... I decided my first project would be the adjustable scope mount.... I haven't machined the radius into the bottom to fit the barrel yet, but the rest of it is finished.... The base will sit on a 20 MOA slant, to put the scope centered at 100 yards, and the adjustment gives me a total of 140 MOA up from there in seven 20 MOA steps, for a total of 160 MOA from the boreline.... The secret is in the asymmetric octagonal cam.... Here is a photo of the top view of the parts....
(https://hosting.photobucket.com/images/oo221/rsterne/Parts_Top.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Parts_Top.JPG)
and here is the bottom view of them....
(https://hosting.photobucket.com/images/oo221/rsterne/Parts_Bottom.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Parts_Bottom.JPG)
On the top is a 6" long Picatinny rail, with the cam follower bolted to it.... The groove on the bottom of it is to locate the upper arm of the spring, which is from a clothespin.... The middle portion (bottom in those photos) has a large groove machined into the top to hold the spring, two threaded holes to mount the Picatinny rail, and on the bottom it is machined to clear the mounting screws and the bump in the baseplate.... The shouldered pivot bolt, and the cam mounting screw, are threaded into the side of it.... The baseplate is an "L" shape, machined from a 3/4" x 1" bar of 6061-T6 aluminum, the same grade material is used for the other parts.... There are two mounting holes on 4" centers, and the vertical part has holes for the shouldered pivot bolt and the cam support, which have very close tolerances to minimize play.... The "bump" has a transverse hole to accept the bottom leg of the spring.... Here is a photo showing the spring and cam in place....
(https://hosting.photobucket.com/images/oo221/rsterne/Subassembly.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Subassembly.JPG)
The next photos show the mount assembled.... The first two are the right side, showing the mount at minimum and maximum height adjustments....
(https://hosting.photobucket.com/images/oo221/rsterne/Right_Low.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Right_Low.JPG)
(https://hosting.photobucket.com/images/oo221/rsterne/Right_High.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Right_High.JPG)
The next two show the left side, again at the lowest and highest settings....
(https://hosting.photobucket.com/images/oo221/rsterne/Left_Low.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Left_Low.JPG)
(https://hosting.photobucket.com/images/oo221/rsterne/Left_HIgh.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Left_HIgh.JPG)
To adjust the height, you loosen the two screws on the right side (cam and pivot) a half turn, and turn the knob to the height desired.... It has a nice snap from one position to the next because of the generous flats and the spring tension.... When you reach the height you want, you snug the two screws up again, to draw the middle section against the vertical part of the baseplate, while pinching the cam against it as well.... The cam screw moves up and down with the mount, which is why there is an asymmetric hole through the cam.... When the screws are tight, the mount is completely rigid....Here is a photo of my Vector 8-32 x 50 Sentinel scope adjusted to the maximum tilt....
(https://hosting.photobucket.com/images/oo221/rsterne/Vector_Scope_High_Mounted.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Vector_Scope_High_Mounted.JPG)
I will be mounting this setup on my .183 cal, on the bull barrel, just ahead of the loading port.... I have already determined that I can get the required eye relief with the scope, and as you can see, it will clear the barrel at maximum tilt.... First part of many, basically finished.... 8)
Bob
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Very nifty, Bob!
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Glad to see and hear you are making chips!
Appears the mount is going to be pretty solid. Nice work 👍
Dave
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I got my lathe repaired, so today I roughed out the two tank blocks.... My milling attachment for the lathe has a vice that is only 1" x 2.5", and opens just 2.3", so I had to mill the middle of the 1.25" thick block to fit into it.... ::) .... I had to turn the block end for end, and make one block on each end.... A lot of it will get cut away to shape it.... Here is the one for the 18 x 1.5mm Regulator (for the .183 cal)....
(https://hosting.photobucket.com/images/oo221/rsterne/18mm_Reg.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/18mm_Reg.JPG)
and here is the one for the 5/8" x 18TPI Regulator (for the .22 cal)....
(https://hosting.photobucket.com/images/oo221/rsterne/5-8_in_Reg.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/5-8_in_Reg.JPG)
All four of the threaded holes for the tanks are 18 x 1.5mm.... I have some all-thread studs made from Metric bolts to attach the tanks.... The smaller through holes, which will be on the front of the tank blocks, have yet to be threaded 1/8" NPT, one for a gauge (tank pressure) and one for a male Foster fill fitting.... I also need to drill the air passages to connect the tanks to the regulator, and plug them at the bottom with threaded plugs with O-rings.... Once all that is done, then I can cut and mill away all the extra material....
Bob
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I have the tank blocks pretty much finished....
(https://hosting.photobucket.com/images/oo221/rsterne/Tank_Blocks.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Tank_Blocks.jpg)
The 18 x 1.5mm studs are done to mount the bottles, the air passages are drilled to connect the bottles to the regulator, and the outer end of them is drilled and tapped 10-32 for plugs, which are a simple low-profile SHCS with a 5/16" OD O-ring under the head, fitting flush in a milled hole.... I have used these before and they work perfectly.... You can see one of the air passages in the right hand hole in the left hand block, and you can see the two 1/8" NPT threaded holes in the bottom of those, which allow a male Foster and gauge to be mounted on the front of the block.... The two tapped holes in the bottom of the tank blocks are to allow me to mount a Bipod, borrowed from my .257 Monocoque PCP, if I want to.... Here is a photo of it, mounted to the front tank band from that rifle....
(https://hosting.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/.highres/BiPod%20and%20Mount_zpsme3ij8kk.jpg) (https://hosting.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/.highres/BiPod%20and%20Mount_zpsme3ij8kk.jpg)
It is adjustable for height and tilt (the pulleys act as handwheels), and has a level built in.... I probably won't need it on these rifles, because they will sit level on the dual tanks, but adding a couple of tapped holes to allow it to be attached just made sense.... The hole in the right hand tank block is to lighten it a bit, it is for the .22 cal pellet shooter, which will have a carbon sleeved barrel and aluminum plenum.... There was no point trying to lighten the one for the .183 cal slug shooter, as the barrel alone weighs about 7 lbs., and it has two 700cc bottles and a steel main tube.... Probably a 20 lb. gun?.... ::)
Bob
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Did you cut the threads on your lathe, Bob?
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The male threads on the Bipod are threaded rod.... and the studs that will hold the bottles are just shortened 18 x 1.5mm bolts and drilled through for the air passage.... All the female threads were done in the lathe, holding the workpiece in the milling attachment (it replaces the compound feed on the crossfeed carriage)....
(https://hosting.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/.highres/IMG_2998_zpsf903de45.jpg) (https://hosting.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/.highres/IMG_2998_zpsf903de45.jpg)
For large taps, I hold it in the 3-jaw chuck, turned manually.... for smaller taps, just using a piloted tap holder, turned by hand, guided by the 3-jaw.... Here is what I use for tapping large threads, or for doing single-point threads up to a shoulder....
(https://hosting.photobucket.com/albums/oo221/rsterne/Important/.highres/Hand%20Crank_zpsq61ugoc0.jpg) (https://hosting.photobucket.com/albums/oo221/rsterne/Important/.highres/Hand%20Crank_zpsq61ugoc0.jpg)
(https://hosting.photobucket.com/albums/oo221/rsterne/Important/.highres/Manual%20Lathe_zpslymng3n0.jpg) (https://hosting.photobucket.com/albums/oo221/rsterne/Important/.highres/Manual%20Lathe_zpslymng3n0.jpg)
Unplug the lathe, remove the drive belt, and crank by hand.... ::)
Bob
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Thanks, Bob
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Nice update Bob.
It’s always a relief when the drill bit pops out in the right spot when connecting these internal passages. We all have seen a bit wander off course.
Dave
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Using a milling attachment really helps.... The block is held square in 2 planes, and the third can be angled (by rotating the vice) so that the drill bit (when laid across the top of the part while in the chuck) intersects the center of both holes.... Then you set the height in the vertical, and it drill along the course you set.... I have never had a problem.... Of course you have to properly sharpen the drill to have the point on center, or use a new drill bit....
Bob
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I finished up the tank block for the .183 cal today.... The tank mounting studs are fitted and loctited into place, and the regulator is also in place.... I removed the gauge and fill fitting, and moved them to the front of the tank block, and plugged the holes in the regulator with 1/8" NPT brass plugs.... I could then screw the bottles into place, pop the tank spacer in, and slide a tube into place to see how everything fits....
(https://hosting.photobucket.com/images/oo221/rsterne/Dual_700_cc_Tank_Block_and_Reg.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Dual_700_cc_Tank_Block_and_Reg.jpg)
It all worked out exactly as planned.... 8) .... I have to make the adapter to hold the regulator in the front of the plenum tube, but it looks like the whole idea is going to come together.... I will do the other tank block to the same stage before continuing....
Bob
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The bottles are the primary HPA reservoirs, two x 700 cc = 1.4 litres at 300 bar for the .183 cal, and two x 450 cc = 900 cc at 250 bar for the .22 cal pellet shooter.... The regulator is mounted between the "inverted V" shaped tank block and the tube, which is the plenum.... The valve and hammer will be inside the plenum, with the stock on the back of it, and the barrel above it.... The plenum in the .183 cal will be longer (because the bottles are longer) and be made from 4013 CrMoly, running at about 3600 psi.... while on the .22 I will be using 2024-T3 aluminum above the shorter bottles, running at about 2200 psi....
(https://hosting.photobucket.com/images/oo221/rsterne/General_Arrangement.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/General_Arrangement.jpg)
Dotted lines are for the .183 cal version.... where I will be using the adjustable scope mount to give up to 160 MOA elevation (dotted line) for long ranges....
Bob
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Awesome, Bob!
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I got the other tank block finished today, and both assemblies fitted together for the first time....
(https://hosting.photobucket.com/images/oo221/rsterne/Tank_Assemblies.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Tank_Assemblies.jpg)
You can clearly see the difference in the size of the bottles.... One of the 3D spacer blocks my son printed for me is in between the long tanks near the back.... They are going to work great, with a simple clamp (or even duck tape) around the outside to hold the tanks aligned with the plenum tube and rigid....
Bob
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I'm looking forward to seeing how the .183 turns out. I've been fascinated with tiny bore rifles since stumbling upon yours and other .172 builds.
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I finished the Regulator Adapters today, and drilled and tapped them for a (low-side gauge), and for the three 10-32 SHCSs to mount the plenums....
(https://hosting.photobucket.com/images/oo221/rsterne/Regulator_Assembly_and_Adapter.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Regulator_Assembly_and_Adapter.jpg)
The front end of the adapter (made from 1.25" OD 2024-T3) is tapered to match the back of the regulator, and of course bored for the O-rings and tapped 1/4" NPS to accept the regulator output.... I lubed and tightened each regulator to its adapter, and then used the tapered sides of the tank block (they are at 60 degrees to the base) as a reference to orient the gauge and the upper plenum screws.... The lower screw is on the bottom, referenced off the base, and you can just access it with an allen driver between the tanks.... The drilling of the holes to mount the tube is so accurate I can orient the tube any of the 3 possible ways, which actually surprised me!.... 8)
Other than making the O-ring grooves (I will do them along with the ones for the valve, all at one time), the tank and regulator assemblies are now finished, and fitted to the plenums.... Here is the one for the .22 cal pellet shooter, on the 2024-T3 aluminum plenum....
(https://hosting.photobucket.com/images/oo221/rsterne/450_cc_Assembly.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/450_cc_Assembly.jpg)
and here is the one for the .183 cal slug shooter, on the (longer) 4130 CrMoly plenum....
(https://hosting.photobucket.com/images/oo221/rsterne/700_cc_Assembly.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/700_cc_Assembly.jpg)
I should get about 50 shots at 80 FPE with the 39 gr. BBT slug, and about 100 at 50 FPE with a 25.4 gr. JSB Monster pellet....
Bob
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looking great Bob , I went back and looked , whats the length gonna be on the .183 barrel ? i did read that its 7 lbs
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The .183 cal LW barrel is 26", and stock it is 32mm OD (1.26").... The .22 pellet barrel from Mike Niksch (a very slow twist LW) is 28" long, and "only" 16mm OD, but I will be sleeving it up to 30mm with carbon tubes....
Bob
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I started on the valves today by making the poppets.... These valves will be a semi-balanced design, similar to others I have made, but with the balance chamber reversed, with the "cylinder" being part of the poppet and the "piston" mounted on the front of the valve body.... Here is the basic design....
(https://hosting.photobucket.com/images/oo221/rsterne/Reversed_Poppet_GA.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Reversed_Poppet_GA.jpg)
The position of the piston is adjustable to tune the volume of the balance chamber.... Smaller volume acts more like a conventional valve, larger volume "blows open" more, which requires less hammer strike but resists tuning via hammer strike.... Motorhead (Scott) uses this style, and the idea of adjusting it came from sb327 (David).... I decided to make the poppet from 2 pieces, a PEEK sealing portion and an aluminum sleeve/cylinder for the balance chamber.... I was concerned the PEEK may not be strong enough to resist the 3600 psi, and might "creep" over time to pinch the "piston".... Here are the poppets....
(https://hosting.photobucket.com/images/oo221/rsterne/Poppets.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Poppets.JPG)
The one of the right is complete, the other one has the rough machining done, but it shows the internal O-ring to seal the two part together.... The 1/8" stem is threaded 5-40, and when assembled everything is glued up using Loctite 638 (green).... Final machining of the chamber is done after assembly, with the stem in the lathe chuck, to assure alignment.... The inside is done with a 1/4" mill, and the OD is 0.354", which reduces the force holding the valve against the seat by 50%.... At 3600 psi, it drops from 354 lbf. to 177 lbf.... The minimum clearance from piston the chamber will be 0.075", which is 1/4 of the valve throat diameter.... This means the valve can reach full flow without the poppet touching the piston.... That volume can be tripled if desired, to make the valve open easier.... The vent through the stem is 3/64" (0.047"), as is the hole through the side of the stem....
Bob
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Wow, Bob, that is a lot of mechanism in a small space. The potential for such small structures breaking makes me wonder when it is most likely to fail; if ever. If a low strike force valve became self opening because something broke, I hope that occurs after a deliberate shot - when the chamber would always be empty. Not after loading the next projectile, to go off when you are not yet fully lined up on target, or berm.
I am not so much concerned with a bench rifle, as a field rifle where it would be common practice to walk about with the chamber loaded, and either the striker decocked, or on safe. Certainly, safe gun handling should have the muzzle never pointing at something valuable that does not need to be shot. But a stray shot still has to go somewhere.
I am not criticizing the design, but such small parts with a few hundred pound of force on them could be vulnerable to breaking eventually. It is not the holding force that concerns me as much as slamming onto the seat repeatedly. I think your holding force reduction should reduce the fatigue of the parts significantly, which sounds like a good thing.
The small valve stem with a vent drilled down its length seems potentially fragile, but probably less so, because it does not require as heavy a hammer blow as a conventional valve. Am I right that you are making the valve stem from unhardened drill rod? If so, it probably has good fatigue resistance, at the expense of potentially peening at the hammer strike face, or being bent. Although bending would require it being struck slightly off axis, and I don't think there is enough clearance between stem and guide to allow that.
What you are doing is like making a functional piston engine with a tiny bore diameter. Impressive!
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Thing is , all balanced valves have this level of complexity and theyre becoming quite common commerically. A lot of AEA models have them , fx uses balanced valves, so does daystate.Even your everyday action pistol with a spool valve is technically a balanced valve requiring very little hammer to produce the shot. Are they as reliable as conventional hammer valves ? NO .. not from what Ive seen. But Bobs not selling these guns commercially , so thats not an issue.
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As I understand it, balanced valve advantages are low cocking force and reduced vibration, starting from before the projectile starts moving until it leaves the barrel. I can see these being of significant value for high FPE slug shooters.
Any other advantages, such as more consistent projectile velocity or POI (other than from reduced vibration)?
I presume that making the valves more robust will make them heavier, sluggish in opening or closing, require more hammer strike energy, and increase system vibration. Unless materials are optimized for properties and just the right amount of material is used in the right location.
One possible improvement, if this was a commercial valve would be to harden the stem, then give it a spring temper. Something stiff and very strong, but with very good fatigue properties. Don't know how to improve the PEEK valve seat. A narrow sealing area is going to take a beating eventually. A bit like a racing engine: You accept a shorter life between rebuilds for increased system performance.
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Hey Bob,
If you’re concerned about the peek wanting to collapse (or yield), you might consider glass filled stock. I use glass filled pei for mine and haven’t had issues.
Subscriber,
The concern over the stem is not necessarily warranted due to the fact the hammer strike is SIGNIFICANTLY reduced with a bv. Also, the closing force is no different than a normal poppet valve so the concern with the seat being beat up is no different than any other valve.
Dave
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Thanks, Dave. A lighter hammer strike would mean the valve stem does not work as hard.
It is not only closing force with the valve closed, but closing speed and valve mass that predicts closing impact. That said, if any given valve configuration lasts long enough, then what does it matter if there might be a better material?
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Thanks, Dave. A lighter hammer strike would mean the valve stem does not work as hard.
It is not only closing force with the valve closed, but closing speed and valve mass that predicts closing impact. That said, if any given valve configuration lasts long enough, then what does it matter if there might be a better material?
harder materials are easier to unseat.. soft materials like nylon take more hammer pressure to get off the valve seat
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sub, I understand your concerns.... During development over the past few years, balanced valves had indeed had failures.... My first was the "spider" at the front end of my first one failing....
(https://hosting.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/.highres/Broken%20Valve_zpsa3kdn2zs.jpg) (https://hosting.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/.highres/Broken%20Valve_zpsa3kdn2zs.jpg)
In the search for minimum restriction at he front of the valve I made 4 kidney-bean shaped holes, and after 100 shots or so, they broke.... The next version had eight 5/32" holes, and each web was twice the depth, so over 4 times as strong.... The area of the holes is still over twice that of the valve throat, and no more failures.... Marco has had several "cages/spiders" break in his 20mm, but his valve is designed to blow open quite violently, as he doesn't care about efficiency, just maximum power.... With such a design, the poppet collides with the front portion of the balance cylinder, and can put thousands of lbf. on the spider, particularly if there is no O-ring buffer between them.... I have always used such a buffer, because if it only collapses 0.025" it reduces the peak force by a factor of 10 or more....
I have never used hardened stems, or hammers, in any of my builds.... My .457 Hyabusa had a 1/2 lb. hammer that took nearly 30 lbf. to cock, and it never showed signs of the collision between hammer and stem.... so I think that worry is overblown in PCPs.... Has anyone ever seen a stem peened, or a hammer dented?.... Yes, I have seen photos of thin stems bent, of course.... The hole in the stem is 3/64" (0.047"), and the stem is 1/8", so the reduction in compressive strength compared to a solid stem is only 14%.... The threaded portion is inside the poppet, so much of the forces are distributed.... Most poppets are simply pressed onto the stem, mine are threaded on....
Another point of failure I have experienced is having the O-ring on the stem of the balance chamber pull the end off the stem, and I'm not the only one.... I increased the distance between the O-ring and the end, which cured that, some have gone to metal stems, which is my choice on this design....
While it seems like there is a lot going on in a small space, I have done what I can to prevent failures.... I may still have missed something, and you are correct some failures in balanced valves can cause the gun to fire unexpectedly.... Those that have occurred to me have just resulted in the opposite, an inability to fire, requiring emptying the reservoir to disassemble.... Thanks for your concerns, they are very welcome, as it is always possible to miss something, and safety is always paramount....
Bob
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Thanks, Bob
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Seeing that damage reminded me of this one....
(https://i.imgur.com/Dkt55f6.jpg)
(https://i.imgur.com/dtUKb43.jpg)
This is from when I was being hard headed and insisted on running a peek seal on a modified Cothran valve. Just the right (wrong) amount of hammer preload resulted a tank dumping machine gunning episode. The Cothran sucked the valve return spring over the poppet, wrecking the valve seat in the process. For good measure, the muzzle blast proceeded to scatter my chronograph and light kit across the shop.....
In hindsight, I did not understand how to properly size and locate the vent. This all happened by combining a vent that was way too big, too much balance chamber volume, super hard poppet material, and then some idiot trying to force the valve to dwell by leaning on hammer strike........
I recall being extremely frustrated for a week or two before finally giving up on the peek and going to a delrin seal..... Lots of nitrogen and lead went to waste during that episode.
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This kind of makes me wonder, with small calibers like .184 do we really benefit from balanced valves? Couldn't we just use 2mm valve stem and PEI poppet to get the long dwell with reasonable hammer strike while keeping it all simple and robust? After all we are now talking about small throat diameter valves and thus much reduced force keeping the valve closed.
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This kind of makes me wonder, with small calibers like .184 do we really benefit from balanced valves? Couldn't we just use 2mm valve stem and PEI poppet to get the long dwell with reasonable hammer strike while keeping it all simple and robust? After all we are now talking about small throat diameter valves and thus much reduced force keeping the valve closed.
good point..
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Quite possibly.... However, I am not scaling down these valves, they were designed for a .257 cal, and I am simply going to taper the transfer port from valve to barrel.... This is partly to hedge my bets because the longest (only) barrel I could get for the .183 cal was 26", and I want to run regulated, so the most pressure I can run (and what I ordered the regulator at) is 3600 psi.... Otherwise I won't get enough shots for a benchrest gun, even with having 1.4 liters of 300 bar air on board.... I figure I can always throttle the gun down, and it doesn't take ridiculous amounts of hammer strike to make a valve of this size work, it is based on the ones in my last two Sporters.... The .172 and 6mm are regulated at 2800 psi and the .224 and .257 are unregulated at 3800 psi....
Besides, I can always make a small-stemmed conventional valve if these don't work out.... ::)
Speaking of not working out, I had to scrap the second poppet above.... The vent wandered off-center to the point it was coming through the side of the stem and I had to scrap it.... Since the regulated gun will be running "only" 2200 psi, I decided to make a single piece PEEK poppet and lose the aluminum balance chamber.... The dimensions are the same, just all PEEK (and the steel stem).... The vent is drilled beside the stem, just though the PEEK.... WAY easier to make.... 8)
Bob
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Well, I got the valve bodies roughed out today....
(https://hosting.photobucket.com/images/oo221/rsterne/Valve_Bodies.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Valve_Bodies.jpg)
You will notice that one of the poppets is now all PEEK, as one gun is only 2200 psi and others have reported no problems at those pressures with similar dimensions.... If you look closely on that one, you can see the concave seat, machined with an 5 deg. undercut so that it only seals around the outer edge.... Also, I didn't have to drill the stem for the balance chamber vent, there was enough room beside the stem, through the PEEK....
Next is to machine the cage/spider for the front to fit in that recess, retained by a snap ring.... All the port, retaining hole and O-ring machining have yet to come....
Bob
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This thread is another treasure trove for those designing improved PCPs for commercial production. Keep it up, Bob.
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Well, there have been a few of those.... The SSG, the use of plenums, reversed bottles, dual side-by-side bottles, simplified balanced valves to mention a few.... Not necessarily new ideas (there seldom are) but I did my best to promote these, and others.... I'm glad to see guys on the GTA find them useful, and flattered that many of the improvements in PCPs over the last decade and a half have spread into the commercial realm....
Bob
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This kind of makes me wonder, with small calibers like .184 do we really benefit from balanced valves? Couldn't we just use 2mm valve stem and PEI poppet to get the long dwell with reasonable hammer strike while keeping it all simple and robust? After all we are now talking about small throat diameter valves and thus much reduced force keeping the valve closed.
It's what I do and personally recommend (and have for the longest) for small calibers. This valve otoh probably benefits from being balanced, where as I would have to force an oversized poppet on my small .234" .25 cal throat just to have it make sense to balance. I currently run peek with .02" sealing margins.
The minimum clearance from piston the chamber will be 0.075", which is 1/4 of the valve throat diameter.... This means the valve can reach full flow without the poppet touching the piston.... That volume can be tripled if desired, to make the valve open easier....
Bob
I know .075" lift is where the valve reaches peek flow but wouldn't it need to lift significantly higher to produce max power ie: need more minimum distance between chamber and piston in your adjustment? I know it can be tripled but .075" seems really tiny if I am envisioning the space between between and chamber correctly, my guess is you would run somewhere in the middle?
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The valve will absolutely open more than 0.075" when going for maximum power.... The lift and dwell are inevitably intertwined, for a given pressure, valve and hammer mass.... You don't NEED the extra lift past the 1/4 diameter where curtain area equals throat area, but you may end up with that to get the dwell you require.... On the other hand, every time I have physically measured the valve lift when a PCP is tuned for the knee of the curve, I have never found it to be greater than 1/4 the throat diameter.... If it is greater than that, the gun is more than likely an air hog, and tuned way up on the plateau for the pressure you are using.... That's my experience, anyways.... Having said that, I expect the best tuning volume to be in the middle of the range I have allowed for, and the poppet to never hit the piston....
Bob
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Bob, while it may be the less exotic of the two, I am looking forward to the .22 and seeing your results with the Monster Redesigned pellets. I recently started shooting them out of a cleaned up Fortitude barrel, which i believe is around a 1:22 or so twist. It is sleeved up to 18mm with cf tubing, in a Brod. While I have not tried them at slower speeds, they do not seem to mind running in the 990fps range. They are not as difficult to get running fast as I anticipated---21.5" from barrel port to muzzle, around 2000psi reg. Testing has shown many instances of 2-3 shots in basically the same ragged hole at 100 yards. Unfortunately, more times than not 5+ shot groups open up to 1.5-2". I hope some barrel/breech stability improvements (barrel band at tank block/Cobra reg) will help shrink those groups. I have not tried head sizing/sorting/weighing...
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The valve will absolutely open more than 0.075" when going for maximum power.... The lift and dwell are inevitably intertwined, for a given pressure, valve and hammer mass.... You don't NEED the extra lift past the 1/4 diameter where curtain area equals throat area, but you may end up with that to get the dwell you require.... On the other hand, every time I have physically measured the valve lift when a PCP is tuned for the knee of the curve, I have never found it to be greater than 1/4 the throat diameter.... If it is greater than that, the gun is more than likely an air hog, and tuned way up on the plateau for the pressure you are using.... That's my experience, anyways.... Having said that, I expect the best tuning volume to be in the middle of the range I have allowed for, and the poppet to never hit the piston....
Bob
Makes sense, you need much less lift and dwell at 3600 psi than you would at 2400 psi for the same given power, and a lighter hammer needs more lift than a heavier one (even if marginal and often times negligible) due to the reduced momentum it contains fighting the valve closure.
Are you going to try out x-rings on this build or will you be staying with a traditional o-ring?
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The goal is about 80-90 FPE for the .183 ca (3600 psi), but only 50 FPE for the .22 cal at 2200 psi.... I'm going to start with the same hammer for both, with more spring on the higher pressure....
I have a couple of 1/4" X-rings for the balance chamber piston, and will try those.... Scott (Motorhead) has good success with them....
Bob
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I made the rest of the valve parts today.... the cages/spiders that support the valve spring and balance chamber piston and allow air into the valve, through eight 5/32" holes (over twice the valve throat area).... and the adjustable pistons for the balance chambers....
(https://hosting.photobucket.com/images/oo221/rsterne/Balance_Chamber_Parts.JPG) (http://"https://hosting.photobucket.com/images/oo221/rsterne/Balance_Chamber_Parts.JPG")
I haven't cut the O-ring groove in the 1/4" pistons yet, but they are threaded and loctited to the 1/8" shafts, and are a loose fit in the 5/32" center hole of the spider, to avoid any alignment issues.... When the valve is closed, their normal position will be back towards the seat, with the distance between the end of the piston and the inside of the balance chamber in the poppet adjustable with the 5-40 Nyloc nut.... I filed flats in the piston so that I can use a 7/32" wrench on it to hold it when adjusting the locknut.... I can adjust the clearance from less than 0.070" to over 0.200", which varies the volume of the balance chamber, and so the amount of "blow-open" tendency of the valve....
The valve stem protrudes 0.200" from the end of the valve, and has at least 0.250" of travel before the spring goes coil bind.... The balance chamber has an O-ring for a bumper to absorb any impact and reduce the peak stress on the spider.... Under normal operation, the hammer will strike the valve stem, the lower pressure in the balance chamber will help to lift the poppet off the seat, the poppet will hit the end of the balance chamber piston and the two will travel together, against the spring force, and rising pressure inside the balance chamber, until the travel reverses and the valve closes.... It will be interesting to see how much affect adjusting the balance chamber volume has on the hammer impact required and the valve dwell....
Bob