Any Interest in 6mm ? - Build Thread

[oldpro]

Too much yet to do and learn to have time to write a book.... and I'll be 70 this year.... 

Bob

Fear not my septuagenarian friend your paving the way for others to follow in your foot steps. Hopefully the 20-30 year olds are putting all this knowledge away to use in future endeavors

[skorec]

Too much yet to do and learn to have time to write a book.... and I'll be 70 this year.... 

Bob

Finally I have found  out why you are much/cheerfully more clever than I . I am only 64.

[lloyd-ss]

Too much yet to do and learn to have time to write a book.... and I'll be 70 this year.... 

Bob

Finally I have found  out why you are much/cheerfully more clever than I . I am only 64.

Ha ha, remember when hitting 30, or 40, or even 50, was a big deal?  Now, so long as we've got some semblance of good health, birthdays don't make a whole lot of difference.  I am glad we are maturing nicely, rather than just getting over-ripe.
Lloyd

[rsterne]

sniff-sniff.... you SURE?.... 

Bob

[rsterne]

I got the 18 mm x 1.5 mm regulator from Travis yesterday, and made a "tiny" tank from a piece of 1-1/8 steel roundbar 3" long, drilled 2" deep and tapped to match the regulator threads.... I already have one for 5/8"-18 NF threads, but this is the first time I needed one for a reg. with the larger threads.... I tested it the way it came, and it was set for 1,800 psi, and fitted with a 3K burst disc on the output side.... so I replaced the disc with a 5K because I need to be able to increase the pressure to as much as 3,200 psi, which is the MSWP for the tube on my regulated 6 mm.... From initial testing I wanted to try 2,800 psi, so I pulled the reg. apart and found some very strange looking Bellevilles.... Intead of a simple concave/convex shape, they were stamped with a ridge in them, halfway between the inside and outside edges.... Travis had sent me some standard 0.032" Bellevilles, which I am much more familiar with, so I decided to use those.... A series stack of the 0.032" thick would not allow me to get a high enough setpoint, and I would normally use the 0.047" ones for this pressure, but decided that since I had enough I would try a series/parallel arrangement using nested pairs of the 0.032" Bellevilles.... The data I had said that arrangement would be not quite as stiff as a single 0.047", which meant it should be easier to adjust.... I tried 6 pairs and got an output pressure of just 47 psi  so I added another pair, a total or 14 of the 0.032" Bellevilles, arranged like this....

)) (( )) (( )) (( ))

The reg. body is on the left, and the large end of the piston is on the right.... This arrangement gave me about 2400 psi, and I tried a 0.020" shim and that jumped to 3300.... I ended up with 0.012" of shims and got a nice solid, stable 2800 psi, within about +- 10 psi each time I burped it.... and it returned to the setpoint pressure within a few seconds.... Although the base regulator is Chinese, it has a Delrin ball running on the seat, like the Ninja regs. do.... and seems very stable.... I guess I'll find out if it remains that way in the long term, but I have a good feeling about this combination.... I fitted it to my 500 cc 4500 psi CF bottle, measured up the length I needed to clear the trigger group, cut the tube to length, and set it up in my milling attachment in my lathe to drill the mounting holes for the tank block....

When I made the tank block, I put the holes at a 45 deg. angle to vertical/horizontal, so that I could remove it without pulling the barrel.... This made the setup to drill the holes so that the tank lined up with the trigger group a real PITA.... I ended up using a 5/16" steel rod through the valve screw holes, and a long level with a 45 deg. bubble, and checked and double-checked as I twisted the tube in the milling vice.... I positioned the milling attachment vice in the horizontal and vertical to drill the hole in the middle of the tube, and the correct distance from the end, and with much trepidation, drilled the first hole.... I deburred it while still in place, slid in the tank block and threaded in one screw, and the alignment looked good, so I drilled straight through the tube, and now had two holes.... I loosened the vice, turned the tube 90 deg., inserted the steel rod through them, and used a machinists square on the bed of the lathe to set the tube perfectly, and then checked the distance from the end, and drill the other two holes.... After deburring, all four screws went in with my fingers, and here is the result....



The next thing I have to do is build another set of "guts" for my version of the ART/SS valve.... Based on the results of the first one, I have more confidence in my ability to make a second one that will hopefully work "fresh off the lathe" compared to the long learning process I had the first time around.... Once the second valve is complete, I will be able to assemble the pressure tube and see if it holds air.... The tank / regulator assembly is currently sitting with 1500 psi in it and seems to be holding perfectly.... The plenum is exactly 11" long inside, which makes the volume including the valve 165 cc....

Bob

[lloyd-ss]

Bob,
I haven't run into those ridged Bellvilles that you describe either.  Do they possibly have some special attribute, like increased travel for the given thickness?
Its nice that the 7 pairs worked out so well. That should give plenty of adjustability. I've run into some cases where it was extremely difficult to find the right combo for a desired pressure. You go one way and it locks up, and you go the other way and the pressure totally drops. Looks like you have a winner.

You are using the 2024-T3 1.25dia x .095 wall tube for the plenum?   Should work nice.
Lloyd

[rsterne]

Yes, the plenum for the regulated gun is 0.095" wall, the 0.120" wall I got from you is used in the unregulated (MSWP 4,200 psi).... I am using four 10-32 screws (installed like an MRod) in the valve and fill fitting on both guns.... Here is what those weird Chinese Bellevilles look like....



They are 0.022" thick material, and 0.046 tall.... I fished them out of the garbage to take a photo for you.... *LOL* .... The shims they used were smaller on the OD than the Bellevilles, I guess when they compress they bear on the edge between the outer rim and the angled part of the dish, with the outer edge picking up.... ie the effective OD gets smaller as they compress.... possibly giving a "progressive" rate?.... Maybe they built a better mousetrap and I chucked them.... 

I just looked up the specs on a 0.022" thick conventional Belleville, and using them stacked in pairs, the maximum pressure would only be about 1400 psi.... and this reg. did 1800 stock.... I'm guessing that means these kinked Bellevilles are stiffer for the same metal thickness, which makes sense.... progressive rate, I don't know.... I think they just act like they have a smaller OD....

Bob

[rsterne]

I spent yesterday making the "guts" for my SS valve.... I already had the body done, but this is a fiddly job, requiring accurate turning of the plastic poppet, including the O-ring grooves, spring seat and sealing face, plus drilling for the stem and vent.... and then making the matching thimble that it rides in from steel, and mounting it to the perforated wheel in the front of the valve.... In case you are wondering why I am not showing photographs of these parts, it is out of respect for Travis, who is applying for a patent on the design.... Anyways, I got it assembled last night, and had a slow leak out the exhaust port, which I cured today by taking another skim off the poppet sealing face and re-lapping it to the valve body.... After assembly with the 6mm upper, and a few test shots, it is now sitting for a leak-down test until tomorrow.... I used my "tiny" regulator test tank instead of the 500 cc CF bottle, so that I can drain the gun if it needs work without wasting all that HPA.... Once the gun is fully sorted, then I will simply unscrew the small steel "cylinder" from the regulator and spin the CF tank on in its place.... Here is what it looks like at the moment....



My digital gauge is on the inlet, just so I can keep check on the pressure.... I will tether the gun to my Great White for testing by connecting to the male Foster on the inlet of the gauge.... The regulator is set for 2800 psi, and this gun has not been tested before, previous testing was done on the 300 cc unregulated gun, whereas the plenum on this gun is just over half the size, at 165 cc including the valve volume.... I backed out the SSG gap until I saw a slight decrease in velocity, I would have gone further, but I don't have enough travel with the 11 lb/in spring, I will have to fit a weaker one.... I like to tune so that the velocity is 3-5% below the plateau to have decent efficiency.... I did find the plateau velocity with the three bullet weights I have, as follows....

61.3 gr. Bowman (257420 copy).... 993 fps (134 FPE)
63.8 gr. NOE 245-64 FN.... 971 fps (134 FPE)
73.4 gr. NOE 245-74 FN.... 913 fps (136 FPE)

I also have HP versions of all three, about 3 gr. lighter, which I did not test.... I am pleased that the velocity is very close to the same (within about 1%) with the smaller plenum, although it is over 1.2 cc per FPE so I did not expect a dramatic power loss.... It should be large enough to work fine on the .257 cal. upper as well, should I wish to shoot it on the regulated lower....

Now to get a weaker hammer spring so that I can tune this beast down a bit....   

Bob

[PeterL]

I spent yesterday making the "guts" for my SS valve.... I already had the body done, but this is a fiddly job, requiring accurate turning of the plastic poppet, including the O-ring grooves, spring seat and sealing face, plus drilling for the stem and vent.... and then making the matching thimble that it rides in from steel, and mounting it to the perforated wheel in the front of the valve.... In case you are wondering why I am not showing photographs of these parts, it is out of respect for Travis, who is applying for a patent on the design.... Anyways, I got it assembled last night, and had a slow leak out the exhaust port, which I cured today by taking another skim off the poppet sealing face and re-lapping it to the valve body.... After assembly with the 6mm upper, and a few test shots, it is now sitting for a leak-down test until tomorrow.... I used my "tiny" regulator test tank instead of the 500 cc CF bottle, so that I can drain the gun if it needs work without wasting all that HPA.... Once the gun is fully sorted, then I will simply unscrew the small steel "cylinder" from the regulator and spin the CF tank on in its place.... Here is what it looks like at the moment....



My digital gauge is on the inlet, just so I can keep check on the pressure.... I will tether the gun to my Great White for testing by connecting to the male Foster on the inlet of the gauge.... The regulator is set for 2800 psi, and this gun has not been tested before, previous testing was done on the 300 cc unregulated gun, whereas the plenum on this gun is just over half the size, at 165 cc including the valve volume.... I backed out the SSG gap until I saw a slight decrease in velocity, I would have gone further, but I don't have enough travel with the 11 lb/in spring, I will have to fit a weaker one.... I like to tune so that the velocity is 3-5% below the plateau to have decent efficiency.... I did find the plateau velocity with the three bullet weights I have, as follows....

61.3 gr. Bowman (257420 copy).... 993 fps (134 FPE)
63.8 gr. NOE 245-64 FN.... 971 fps (134 FPE)
73.4 gr. NOE 245-74 FN.... 913 fps (136 FPE)

I also have HP versions of all three, about 3 gr. lighter, which I did not test.... I am pleased that the velocity is very close to the same (within about 1%) with the smaller plenum, although it is over 1.2 cc per FPE so I did not expect a dramatic power loss.... It should be large enough to work fine on the .257 cal. upper as well, should I wish to shoot it on the regulated lower....

Now to get a weaker hammer spring so that I can tune this beast down a bit....   

Bob

Awesome job Bob.

A quick yes or no on the internals of your valve(I'll pm you why I asked this question). Are you using the exact internal as the current ART/SIKES VALVE for sale from Travis or is yours tweaked differently?

Peter

[rsterne]

Nope, not the same.... 1/4" small end, 3/8" big end, 3/8" poppet seal, 1/8" stem, 1/32" vent hole.... "floating" thimble of my own design (5/16" OD at the front, tapers up to 7/16" OD at the back), 1/16" hole in the front mounting screw where Travis uses a jet.... Designed it myself, loosely based on Lloyd's and Travis' prototype drawings....

Bob

[MJP]

Nice work Bob,
Just out of curiosity what pressure do you hydro test your airtubes?
Or do you just relay on math?

Marko

[lloyd-ss]

Bob,
The gun is coming together very nicely.  Your careful pre-planning makes for less tweaking as it goes together, but I know there are still a lot of little things that get "improved" on the spot as the process continues.
Lloyd

[rsterne]

Marko, I don't have the facilities to Hydrotest, I just rely on the Math.... Fortunately, all the testing that Lloyd has done show that the math is, if anything slightly conservative.... in that testing to failure requires slightly more pressure than predicted.... and in every case the weakest link predicted by the math is the part that fails first....

Lloyd.... exactly why I don't make detailed drawings.... dimensions get changed "on the fly" as I make the parts.... to insure assembly goes as smoothly as possible (or is possible at all)....  .... The "planning" and associated drawings is only to develop the concept and workability.... and find major problems before work begins....

Bob

[Finn]

Are you using barlows equation or something else? I have used that with normal tensile stress area calculations for rough estimations and never had an unpredicted failure during hydro testing. Simulation is useful with complex shape objects so that is what I usually do first.

[lloyd-ss]

Are you using barlows equation or something else? I have used that with normal tensile stress area calculations for rough estimations and never had an unpredicted failure during hydro testing. Simulation is useful with complex shape objects so that is what I usually do first.

We were using Barlow's equation for a long time until I started doing calculations for thick walled tubes for pressure testing fixtures. Barlow's formula, which is really just an approximation, is valid for thin walled tubes.  I think thin walled is defined as the wall being no thicker than one twentieth of the diameter. But when the wall starts getting thicker than that, Barlows calculates the stress in the tube wall as being much higher than it really is, making it appear that a much thicker tube wall is required.  I then switched to using the thickwalled formula , calculating the max stress in the tube wall, which is always at the I.D. of the tube wall.

Here are few examples of the hoop stress calculated using a couple of different formulas:

10,500 psi test pressure. .875 tube O.D. and .065 tube wall. Barlows using tube O.D. shows max stress of 70,673psi, Barlows using mean wall dia shows 65,423 psi max stress, and using the (not Barlows) Thick walled formula, max stress is 65,844psi.
That shows good correlation between the Barlows O.D. formula and the Thick walled calc.

But when you go to very high pressures and thick walls the correlation is poor.
30,000 psi test pressure. .625 tube O.D. and .156 tube wall.  Barlows O.D. formula shows a max stress of 60,096 psi, Barlows mean wall diameter shows a stress of 45,096 psi, and the Thick Walled formula shows 50,085 psi.

So, my observation is that Barlows is fine for thinwalled tubes.
But for thick walled tubes, it is best to use the Thick Walled tube formula.
Barlows will cause you to over-design using the O.D. formula; Barlows will cause you to under-design if using the mean tube wall diameter (some people use the mean wall tube dia method); and if you use the thickwalled formula, you end up with a safe tube that is not over-designed.
Just my thoughts on the subject.
Lloyd

[rsterne]

and in case it's not clear.... I use the spreadsheet that Lloyd came up with for my reservoir design, as it includes calculations for the end plugs, either threaded or pinned with screws.... I use a design point of 3.5:1 to failure and 2.5:1 to yield on my builds....

Bob

[lloyd-ss]

and in case it's not clear.... I use the spreadsheet that Lloyd came up with for my reservoir design, as it includes calculations for the end plugs, either threaded or pinned with screws.... I use a design point of 3.5:1 to failure and 2.5:1 to yield on my builds....

Bob

I must add that Bob and I have collaborated on this spreadsheet, along with a few other spreadsheets, adding refinements and features as time passed.  All of the spreadsheets started out at a pretty basic level, but the enhancements are what made them more and more useful. Bob is often the one who suggests the enhancements, and after a few back and forth iterations between us,  we end up with something that we are both happy with.

-------
Finn,
I am curious how you do your hydro testing, if Bob doesn't mind side-tracking the thread for a moment.
Thanks,
Lloyd

[Finn]

I made a hand operated tester pump that goes to at least 600 bar (broken 500 bar gauge told me), pump is connected to the tested part via thin metal pipe and it goes through modified bucket lid. Water filled part is submerged in the bucket and the lid has thin glass tube attached to it. Everything is made watertight and air is bled from the bucket by injecting more water from bottom connector until it almost fills the glass tube. Pressure is built up and possible displacement measured by observing the water level in the glass tube. If the level does not drop after pressure release the part has yielded or something leaks. I dye the pressurized water to see if there was a leak and repeat the tests if needed. Some parts I measure with micrometer before and after. I don't intentionally use the setup for destructive testing.

[rsterne]

I have run into an interesting little hiccup with the regulated gun.... The new valve I made is as identical as I could to the old one.... It functions fine, and reaches the same plateau velocity at the same pressure, minus a few fps for the 165 cc plenum instead of the 300 cc reservoir.... However, it takes MUCH less hammer strike to reach the plateau, and it appears to have very little velocity adjustment range before hitting the cliff.... I am not 100% sure about the latter, because I cannot reduce the hammer strike to the point where the velocity drops much, and then one more turn (but right at the edge of my adjustment) it quits opening....

The only thing I noticed on disassembly is that the shiny mark on the poppet that should indicate where it is sealing is near the throat (5/16") instead of near the outer edge of the poppet (3/8"), where it was on the original valve.... Both surfaces were turned at 90 deg. to the axis of the valve, and have been lapped in.... The big end of the poppet is 3/8", the small end is 1/4".... with a 1/32" bleed hole to the exhaust port and a 1/16" "jet" in the front.... I know that the area of the seal on the poppet can affect how easy it opens, do you think that is what I am seeing.... If so, would cutting a thou or two of concavity in the poppet to force the seal to the outside edge prove that and cure it?....

Lloyd, what do you think?.... Travis?....

Bob

[lloyd-ss]

Bob, Yes, the sealing "ring" being smaller than the large piston diameter is causing the situation.

If we have (at 2500 psi): sealing diameter= .375 dia(276lbs),  large piston=.375 dia(276 lbs), small piston = .25 dia(123lbs), stem = .125 dia(31 lbs), return spring = 4 lbs

The cracking force with .375 seal dia is equal to: sealing dia -large piston + small piston + spring, = 276-276+123+4 = 127 lbs
The cracking force with .312 seal dia is equal to : 191-276+123+4 = 42lbs

Force to close for both situations is stem dia +spring = 31 lbs

That does indicate that you might be able to tune a misbehaving valve a little bit by adjusting the diameter where the poppet actually seats. It also shows that you are getting to the point where the valve might start to machine gun.
Lloyd