GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Show us your Custom Airgun Parts (TRICKS-N-TIPS) => Topic started by: sb327 on November 10, 2020, 09:28:44 PM
-
Been playing with this build on and off for a bit. Got enough done to be able to show some progress.
It is a .32 caliber (32-20, .312”). Really close to a .308.
I’m not trying to build a powerhouse with this. Just a plinker. The valve is a MYOT regulated from eBay.
I only opened one side of the tube for loading. I want to keep as much structure there as possible. The top will be epoxied upon final assembly plus it has eight 10-32 screws to give it the rigidity of a condor.
The grip frame will have eight screws as well but no epoxy.
I’ve still have to make a trigger, sear and linkage. Carve a pic rail on top. Trigger guard. Angle front of top rail. Various other weight loss cuts.
Dave
-
that looks awesome.!
-
Had time to get the sear and trigger done today. Was able to test fire it. My small spring was too weak. So I had to go to a bigger one. I’ll get that sorted later. I hope to be able to use a little easier to cock spring. I need to lighten the breech block slider some. It’s robbing quite a bit of hammer energy.
725 FPS with a 64.5 gr @ 2150 psi
Still have a lot of whittling left to do but at least I know it’s gonna work.
Dave
-
already pushing some good fpe.. pretty cool , i hope some air force builders chime in , Its a platform i know little about..
-
I don’t know much either except they are extremely simple. I’ve wanted one for a while but they are a touch out of my price range. But not out of my machines capabilities.
The valve was cheap, just took a while on the slow boat. I had to make a top hat for the top hat, so it is pretty restricted right there. Like I mentioned though, no plans to hotrod this.
Talontunes was where I figured out how the bits work together, just looked at a bunch of pics and read the descriptions.
Once I get this one ‘done’ (guns are never done), it will be on to tuning this one and my sidelever.
Dave
-
Great work
Can’t wait to see the finished rifle.
Thank you for posting and the pictures.
Look forward to reading your future posts
Thanks again
Dave
-
Thanks for the reply!
When I was researching this project, I found that you can get basically every part. Including an extrusion for the frame. A lot of ‘knock offs’ out there as well.
The most expensive part is the barrel, if buying new.
I think someone could throw one of these together with minimal tooling and time.
When I started building guns, I had little more than a hacksaw, file, grinder and drill. Now that I’m 50, I appreciate the machine tools I’ve acquired over the years.
Airguns have opened up a new door for me.
Dave
-
Cool 8)! I do agree, if you look at it from a purely mechanical standpoint; the Airforce guns are (arguably, there are always different ways to look at it) the conceptually simplest design there is.
More good work, and thanks for sharing.
Jesse
-
I had a little time to mess with this today. After the honey do’s...
Got the top rail machined and turned the breech slider down to shed some weight. (The slider is missing in the pic).
I may take the valve apart and make a peek poppet for it. I’m pretty sure the one that came with it is delrin. And tapered.
Dave
-
I trimmed the top rail back a touch and blocked out a grip and foregrip. It’s some walnut I had left from another project. I still have shaping to do on it. The finish is ‘fake for the picture, just wet it with water to see how it’ll look dark.’ I’ll have to make a wood buttplate too.
I kept the stock valve but changed the angle of the seat.
Anyway, just an update.
Dave
Btw, this thing is FUN to shoot.
-
that looks awesome !
-
WoW.... I've always wondered how walnut furniture would look with an Airforce-style platform; now that I see it I'm thinking it looks waay too cool..... 8)
Jesse
-
A quick question for ya, since I'm considering an Airforce-style setup. How much room do you have to get the bullet/pellet loaded? Is it a pain to have it a open gap, or do you think a loading "tray" like the Texans have would be easier?
Thanks in advance,
Jesse
-
I might have done a loading tray for sure, if I had looked at a Texan close enough to realize that was possible. But, short of soldering one in place, you use valuable barrel length.
I am thinking seriously about going back and doing the soldering option. Not only would it make it WAYYY easier to load but it would fill in a substantial dead space.
I kept my distance short because of the latter. 0.70” roughly. A bit cumbersome but I don’t mind.
Incidentally, I have a .457 Texan on the way. I’m gonna be seeing how they did the valve so I can apply some better flow principles to mine. I have a super choked down system right now.
Dave
-
Thanks; that was just what I needed to know.
Enjoy the Texan,
Jesse
-
The more I learned about pcp’s, the more I wanted a long range .257. So I ordered a barrel from TJ. It’s 35”. Long like a Texan now, lol.
So for the valve....well I decided to make one from scratch. While I was going over it in my head, I decided to try it ‘balanced’.
As built, it should be working as intended. But, I have no baseline to go off of, so I’m gonna make an unbalanced poppet to see what the difference is.
I was quite pleased with the numbers it’s making as configured. Starting at 3250psi, down to 1800psi, .22liter tank, 13 shots average 130fpe. Shooting cast 70gr. Fastest 958fps, at 2900psi.
Accuracy was not bad but I was mostly getting my scope dialed in while getting some data.
Anyway, that’s my update on this build.
Dave
-
Btw, the poppet is Utem 2200 20% glass filled PEI.
Dave
-
Cool!! :D I think that you may be the first to try to make a balanced version of the Airforce inline valve... It will be very interesting to see how the unbalanced poppet performs in comparison... Did it seem to take a significantly less amount of hammer weight/power than you expected?
Jesse
-
Not as little as I’d hoped but again, I have no baseline. My Texan is sidelever so really no idea.
If someone who has shot a Noble type setup could comment on cocking force, it would be helpful. I see pictures of his with large cocking knob mounted to hammer.
Dave
-
awesome Dave.. trying to wrap my head around the balanced tank valve .. very cool
-
I'm still trying to understand where the valve seat is on the poppet?.... ???
Bob
-
The seat must be inside the outer shell of the valve. very interesting.
so when the valve opens, air flow through the 3 holes next to the valve stem
====
i take that back...i am in the same boat
-
It’s in the valve body.
5/16” throat with 1/8” stem. Stem is a sliding fit, no reason to try to hold it tight in this setup. Back of barrel/sliding breech capture top hat.
I’ve got a sketch I built it from, I’ll try to find.
Dave
-
Here it is. Some dimensions got changed but this is the idea.
Dave
-
Ahh, OK, so the poppet seat is on the flat end of the poppet where the 3 holes are.... Got it!....
It looks like the O-ring on the stem and the one on the top hat are the same diameter?.... If so, then no net opening or closing force on the stem, right?.... The balance chamber offsets some of the cracking force, but once the pressure in the balance chamber equalizes (pretty quick with 3 vents) the only closing forces will be from flow resistance past the poppet head and through the 3 holes in the stem, plus the valve spring.... I'm guessing you have a pretty beefy spring to avoid a tank dump?.... Sorry, got that backwards for top hat and stem being the same diameter, very little valve spring is required... :-[
Bob
-
You are correct Bob. No net closing force besides the spring. I started with a beefy but couldn’t make power so went lighter. No tank dump.
Now, if someone can explain the closing ability of an Airforce, I’m all ears. I’m hitting this thing pretty hard. I left plenty of travel for dwell. So no bouncing off the backside. I’ve had no tank dump.
If you look at my tx2 valve on my 45, it has a net OPENING force and doesn’t experience tank dump till 23-2400.
Part of my reason for playing with this idea is to try to better understand what is going on in an af style valve.
Dave
-
Oh, and yes, I was only trying to eliminate cracking force on this initial try. I wanted as little ‘blow open’ as possible, allowing the piston to float.
Dave
-
seems like a good product on your hands , assuming it transaltes well to the larger bores
-
I’m not breaking any ground. I’m really just playing, learning a little. I did get the performance I wanted, but that’s been done. Doug Noble can do that with his eyes closed. I do think it is doing good efficiency wise.
Here is a tx2 valve for 45 for you fellas to look at. There are 5x .156” holes in the top hat.
Dave
-
Here is a drawing of a stock AirForce valve showing the closing forces at work when the valve is open....
(https://hosting.photobucket.com/albums/oo221/rsterne/257 Condor/.highres/Condor Pressures_zpssxqibxu7.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/47e225fe-debc-45b3-b424-216ee17f5a07/p/eb4051d0-d2cd-4bb2-b49e-040e104e4418)
This may have been well understood before I drew this up, but I had never seen anything similar, either drawn or written about.... Of course when Doug Noble saw it he said "yep, you got it right".... ::)
If the top hat and stem are the same diameter, the valve does not blow open, all the work must be done by the hammer.... If the top hat is larger than the stem (D > d), then there is an opening force once the valve is cracked that assists the hammer strike.... The higher the Sectional Density of the slug, the slower it accelerates, so the higher the pressure on the front of the top hat, and the further it blows the valve open.... Carried to the limit, that can cause a tank dump....
In addition to the valve spring, the air rushing past the poppet provides some closing force.... and particularly in a stock valve (where the holes in the stem are drilled at 90 deg.) the air rushing though the throat and hitting the stem adds some closing force as well.... When you angle and streamline those ports, that closing force to a large degree disappears, and you can end up with a valve that does not respond well to changes in hammer strike.... The valve tends to either open wide or barely crack, causing a "cliff and plateau" response to the power wheel setting.... ie the valve either cycles properly or it doesn't....
When D = d, you need more hammer strike, so the valve once again begins to respond to the power wheel setting.... particularly if the valve spring is weaker.... Doug Noble uses a stronger hammer spring, lighter valve spring, and a heavier hammer to gain tuneablity in his high power valves.... ;)
Bob
-
That I do understand and I have seen your write up on it. I believe it relies heavily on the flow around the poppet (sail) coupled with whatever other forces (example: friction of flow through stem holes) AND a significant drop in pressure at the top hat OD for it to blow closed. It’s that significant drop in pressure I’d like to get around. That tx2 of mine has a relatively small hole for caliber. .325 vs .45. That would give it a pressure differential once Elvis has left, but I feel it wastes air and could be improved.
My valves efficiency is pretty good and performance is where I want it. Now I’d like to see if I can make it easier to cock. It’s not unbearable but would be nice if easier.
I’m sure mine has no ‘blow open’ advantage which I believe makes it less likely to dump but harder to get to dwell. I’m planning to try conventional poppet then start venting slowly. I also will see what letting the poppet ‘float’ on the stem will do when the bv vent is tiny....may blow it right off and dump for sure :o
Dave
-
Well it is official, the bv is definitely making a difference. With a plain poppet, it only gets 511 FPS at 3000 psi.
My next test is to drill a small vent.
Question. What size hole and how far back to set piston?
Dave
-
No idea where you are planning on venting.... Are you talking about through the poppet from the throat to the balance chamber?.... If you don't already have a vent there, I don't know how the valve is closing at all, frankly.... and how does the pressure in the balance chamber stay at atmospheric when the valve is closed to create a balance....
I am not familiar with the TX2 valve, nor have any ideas what the holes in the top hat do.... ???
Bob
-
I just made a plain poppet. Bv style with no vent just to have a comparison to my vented one. I reported that difference above.
Now I want to start venting it a little at a time to find a sweet spot or see what the difference is between big vents (little blow open) and small vents. I know how it normally works in a non-af, just curious here.
I’ll see how small of a drill I have and go from there.
Dave
-
Well I have smaller but decided on a .029”.
Not very scientific testing here but I was able to move the bv piston further back for some comparison testing.
Initial setting 660fps
Initial +.062”—770fps
Initial +.125”—885fps
These were with a lighter hammer spring. I did not shoot a string. Just a couple shots each setting at 3000psi.
Keep in mind the poppet stem can slide easily in the top hat. So the top hat movement cannot close this poppet. Only open.
Dave
-
your previous posts stated a 62 grain going at 725fps. but now its going 500fps. and i dont see the BV speed anywhere.
can you post all the numbers on one post for comparison please?
-
I’ve only shot 70 gr since the caliber change to .257.
My first heavily vented bv with heavy hammer spring
“I was quite pleased with the numbers it’s making as configured. Starting at 3250psi, down to 1800psi, .22liter tank, 13 shots average 130fpe. Shooting cast 70gr. Fastest 958fps, at 2900psi. ” (from reply#15)
Then I tested same spring with conventional poppet (no balance vent). That is when I got 511fps.
Then I vented (making it balanced) to .029” and tested at various piston positions with a lighter hammer spring.
Dave
-
With no vent, there is no guarantee that the balance chamber is coming back to atmospheric pressure between shots.... If not, then it may not be doing any "balancing" at all.... In fact, if the pressure inside creeps up to 3000 psi, it would act as an air spring (adding to the valve spring force).... IMO you need "some" venting or it's not a balanced valve, at least not reliably....
Bob
-
Bob,
It has a .029” vent, sorry for the confusion. I only tried it without a vent just for a reference of straight poppet design. Then I drilled the.029” vent and started moving the bv piston out a little at a time.
(Reply#33and34)
So I put the lightest hammer spring I had in. I set just enough tension on it to get the valve to crack and allow poppet to blow open.
So now the shot cycle is completely dependent on the balance valve.
I shot a string of 10 shots. As expected it has a declining shot string.
Starting at 3200psi down to 1900psi
1017
1007
1003
987
980
967
948
928
902
879
961.8 avg
It is pretty easy to cock now and I can tune it via position of my bv piston.
My next testing will be with a bigger tank to see how many accurate shots I can get and some tethered. I don’t have many bullets left though. Have to order some more. I do plan on making a swaging die for this one, just don’t feel like it right now.
Dave
-
All I have to say is :D
Jesse
-
If nothing else, it’s interesting and has been a fun project. I think it will be fine for hunting. I replaced the little 220cc tank with a 450 (I think, have to check for sure). I shot 5 shots to zero the scope and these were the velocities. (Converted from meters)
994 (possible stiction in bv, not bad though)
1003
1000
997
987
I started at just a touch above 3000psi
I measured cocking force with my fish scale, it’s about 16lbs.
Dave
-
Great job!....
Bob
-
Thanks Bob. The efficiency isn’t too bad either. Loyds calculator shows it as a 1.2 with the data from the string I shot with the little bottle on.
Dave
-
Oh one more interesting thread I have missed,
Good job!
Marko
-
I have more to do on this. I haven’t even stretched its legs with this balance valve.
I know at some point the barrel will get cut down some and I have an idea with the valve I want to try. Time is my only limitation. Seems everything else gets my time and I don’t have much left over, lol.
Thanks for the reply.
Dave
-
I know the feeling, everyone wants a minute of your time and there are only so much hours to spare.
Not even close to enough hours in a day to do everything I would like to do. And there are the things I need to do and dont even like.
Marko
-
I’m still messing with this one as time permits. I’ve changed the barrel to a Douglas 27” and upped my starting pressure to 3600 psi. (I’ve tested to 3750 and that lightweight spring still gives a regular shot cycle).
My velocities are just under 1000fps starting and accuracy is more than acceptable for hunting.
I want to try a little bit longer slug. Right now I’m shooting a 75gr. BBT from a mold I made with a little cnc table I made for my mini lathe.
Dave
-
Good looking bullet!
Would be interesting to see how you made it.
I just love diy cnc stuff, and its interesting to see other machines.
Marko
-
I’ll try to get some pics of it. Super simple and cheap. I am using grbl and no spindle encoder so no threading capability. It’s really just for molds. It’s just x and z built on top of a different saddle, that way I can get it out of the way for manual work.
Dave
-
Here it is. Just kinda pieced everything together on the cheap. Mostly eBay stuff. Steppers with leadscrews so not really robust.
The controller is for one of the cheap cnc router. (3018). Cheap and easy to use. Arduino based grbl. I run it via usb from UGCS on my computer.
I use freecad to model and fusion for cam. I’m still learning the cam stuff. And how to manipulate my gcode for clearances and such.
I tried homemade hss boring tools but they flex too much. I ended up getting solid carbide and reshaping to what I wanted.
Dave
-
nice.. freecad has cam also , granted i never figured it out and stuck to fusion.. Universal gcode sender is really handy.
-
That is just genius using a second slide with cnc in it.
What is that boring bar, any link for it? Looks some like sandvik mini but not sure?
Marko
-
It’s a cheap kyocera https://shop.kyoceraprecisiontools.com/products/8513232
I have a micro100 brand that I got before finding these cheap ones. It was around $25.00. Can’t figure out the price difference…
Dave
-
Thanks David,
Need to check it out.
Marko
-
I bought the Kyocera from eBay. I just went to the link I posted and apparently it is all just liquidation stuff. Hmm, I better get what I need while they are cheap.
That explains the price difference.
Dave
-
I am starting something similar.
Does anyone know what the threads are on an AirForce Edge tank?
-
I’m not sure on the Edge, hopefully someone will chime in with a definite answer.
Dave
-
Should the same on all AF bottles m18x1.5
Marko
-
PCPMart has an adapter for Airforce tanks and shows that it has 7/8-14 UNF threads?
-
I'm pretty sure that 7/8"-14 is the threads that insert into the back of the Air Force receiver (the front threads on the valve), not the bottle threads.... All HPA bottle threads I have seen are either 18mm x 1.5mm or 5/8"-18 NF.... The Talon/Escape uses the smaller (5/8" - paintball) threads, the Condor and Texan use the larger (metric) threads on the bottle.... The Edge, I don't know.... It's tank is just a tube, not a bottle....
Bob
-
My plan is to use an edge tank as the basis of a compact PCP, so it is the threads that go in the receiver that I need to mate with.
I had originally thought they were the same as any CO2 paintball tank - but they are not....
-
The threads that slide through the frame in a Condor at 7/8"-14, in other words the hole in the frame is 7/8"... The tank is attached by a "spin lock" nut inside the loading port of the receiver, the tank does not thread into it.... I can't imagine that the Edge uses a different frame.... Measure the OD of the tank threads and the ID of the frame and you will know for sure....
Bob
-
Aha, it seems the reason for my confusion is that I used to have a Condor that was made before the spin loc tanks - so the tank threaded into the frame.
My idea for my current build was to make the frame from 1" ID aluminum tube and modify a fill adapter (like the one I had for my Condor) into a bushing.
Since I have a couple of CO2 tank top adapters, I was going to use one of them.
But those threads are not the same as the Edge tank's.
The OD of the Edge tank threads are 0.850" and the PB tanks are 0.820"
So does anyone know what the 0.850 diameter corresponds to?
-
I use the locking ring that came with this brand of valve.
Dave
https://www.ebay.com/itm/292329486673?hash=item441031f951:g:f2sAAOSwc1Zb3viH (https://www.ebay.com/itm/292329486673?hash=item441031f951:g:f2sAAOSwc1Zb3viH)
-
Aha, it seems the reason for my confusion is that I used to have a Condor that was made before the spin loc tanks - so the tank threaded into the frame.
My idea for my current build was to make the frame from 1" ID aluminum tube and modify a fill adapter (like the one I had for my Condor) into a bushing.
Since I have a couple of CO2 tank top adapters, I was going to use one of them.
But those threads are not the same as the Edge tank's.
The OD of the Edge tank threads are 0.850" and the PB tanks are 0.820"
So does anyone know what the 0.850 diameter corresponds to?
prob m22
-
or a very loose 7/8".... Get yourself some cheap pitch gauges, imperial and metric, and you can quickly determine the pitch.... What is the ID of the Edge frame?.... You keep calling these threads the "tank threads", but they are actually the valve thread, that attach it to the frame....
I have 2 Condor tanks here with valves installed, plus 2 aftermarket (Chinese?) valves (one is regulated).... The AirForce threads measure 0.872" and 0.875" OD, the aftermarket measure 0.852" and 0.857" OD.... I have a spin-lock that threads onto all 4, but is obviously a looser fit on the aftermarket ones.... However, they are all the same pitch, 14 TPI.... There is no air pressure on the threads, the only force is the pressure acting on the OD of the top hat during firing.... With a 5/16" top hat, at 3000 psi, that is 230 lbs.... Even the loosest fitting spin-loc threads are plenty strong enough for that....
Bob
-
You are correct, it is the valve threads that I am referring to - I call them tank threads since I have no intention of disassembling the tank.
I did make a PVC bushing for it using a 1/2-14 NPT tap. It's not a perfect fit but it works.
Which points to it actually being 7/8-14
If it doesn't hold up, on to plan B.
Thanks for all the guidance
-
the 0.820"x14 thread you referred to earlier is 1/2" NPS (straight pipe thread).... It is the same pitch as 1/2"-NPT, but not tapered.... If you are holding the tank in place against breech pressure, I'm not so sure I would be using plastic for the bushing.... Obviously, for any greater force, it would not be sensible either....
Bob
-
Good point - thanks
-
Here is something interesting (to me at least)
I found this nut om my misc. box - I think it's from a toilet valve.
Looks like it fits perfectly
(https://lh3.googleusercontent.com/pw/AM-JKLVlXBPU2LG8QH3tMdDcBqjsmxbIYmtHcBJdxgDhEGI9PiGm6I2DPuwcYSV7Lf8csG5dcSREl9I7iUX-4rkAIfl_vLAdMuMOeuVczbz1ss_xbKvPgp3Nau4O4YuGpNGBr4cQamGgqKC686cQdvWr-Fqq=w1038-h943-no?authuser=0)