GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: JuryRigger on November 20, 2020, 11:34:02 AM
-
I have been working on several different configurations for this build for some time now; I think that I have settled on a final arrangement. I am trying to achieve 60-ish FPE from a self-contained platform; using as few additional purchased components as necessary. I still have much engineering work to do, I have only done some rough calculations on the tube's strength and believe it will suffice.
I am going to roughly mock an Airforce Condor/Edge, in the overall drawing the main tube will serve as both the tank and the frame. I will be using 1" OD .120" wall 1020 DOM tubing that I already have; it will stay as one piece to form both the tank and the frame. I estimate that I will have an 85 CC reservoir, which will be run at approximately 3000 PSI. The tube has sufficient thickness for the forend/trigger block and top rails to screw on; the pump tube will be joined to the tank through a banjo-bolt type setup. I mocked up a breech/hammer design based off eye-ball "scaled" pics of components for Condors on the web; it was only for me to get an idea on overall size, if anyone has solid information on Airforce Condor/Talon valve/breech/hammer design , it would be helpful. I will post pics of the other configurations that I thought of, if they could be of help to anybody. It will be a while before parts actually begin to be made; I am staying at home due to COVID; and have no machine tools. As of the moment; I am currently building a small lathe, approx. 3" swing by 22" between centers. It should be of sufficient size to perform all required turning for this build; the other parts that would require milling will have to be able to be filed out.
I will post revised drawings/other design concepts as I get them drawn out.
Here goes:
-
my only advice, MORE leverage.. but it makes peerfect sense ,. and this configuratioin might actually save you sopme fabrication.
So 1 " -.240 = a .760 piston. Past about 2200 psi that will be very hard to pump with a standard single pivot linkage. turning the pump sideways and having a long sidelever would make it easy..
the force required for 3000 psi is 1360LBS on the piston face.So even at 20-1 mechanical advantage youre still pushing 68lbs on the final pumps.( dont get me wrong 40-1 or 60-1 are very possible,) . And that all sounds fine , but these numbers assume ideal efficiency , no friction, no losses and so on. food for thought.
-
Good point Rob, I "modeled" the stroke at various points and I thought it would work, but having never owned/handled a pumper I have no way to "gage" ideas compared to a real-world experience... I have a compound linkage idea I'm playing with, it is a variant of an design posted here for an SSP a long time ago... I still have to draw it up, but might have it posted tonight.
Thanks for the feedback,
Jesse
-
an easier way to get it all going would be to chop an existing pumper , lets say a 760 since its cheap etc//
solid flat top internals ,pinned valve , and use the existing valve as your check valve ( since it has one alrerady ) remove the stem and poppet , have it fill your 80cc section of tube which connects to the airforce valve .
-
Rob, cannibalizing a 760 or other pumper would be a good idea; but as of now I am currently trying to keep costs at an absolute dead minimum. I already have a gage, silicone grease/oil, a stick of 3/8" PEEK, and enough random steel/stainless/brass and bronze stock for all mechanical components. I will only have to purchase the seals, the barrel, and valve pinning/other hardware (plus a hammer spring). I even have a scope.
This is the SSP linkage that I based my design upon:
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=180377.0;attach=336698;image)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=180377.0;attach=336700;image)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=180377.0;attach=336702;image)
I am truly sorry, but I cannot remember who to credit with this design; IIRC it was developed by a member here in an attempt at a 12-20 FPE SSP to produce for sale.
The intriguing part of this linkage (to me) is the ability to use almost the whole pump tube length as swept volume; in my case clearance becomes an issue as well as stability of the long thin pump rod. In my drawing, I have shrunk the pump to .75" OD .62" ID tubing; with a stroke of 2.87" so displacing .86 cubic inch. I may enlarge the pump tube to gain more swept volume; but as-is the reservoir/plenum should be big enough to give 2-3+ solid shots; enough for hunting so I am not overly concerned with rapid recharge-ability. As can be seen, the leverage ratio increases as the lever is brought home; at .090 headspace or approx. 462 PSI, there is still 4" of lever travel to go. That gives a minimum leverage ratio from that point forward of 44.4 to 1, the handle force at 3KSI will then be .62" dia=905 lbs thrust /44.4= 20 pounds. That would seem a reasonable effort; if I up the tube volume to .76" ID it would be about 1.5x that or 30 pounds; then giving a swept volume of 1.3 cubic inches a stroke.
Jesse
-
i beleive the 2 arm wine bottle opener design was patented by crosman for the turbo air pump they never released.. and agreed , its maximizing the use of the tube length.There was also an ssp builder using the same linkage on youtube. The reason i mention the cannabalized parts, is that fabbing a pumper linkage , piston , and so on is very time consuming.
-
Very true, it would save time... I shall think about it, as it will be awhile before I can start making chips anyhow.
Jesse
-
I will definitely be following along. I think you have an interesting concept there. I really don’t have anything to add except encouragement.
I really like scratch builds!
Dave
-
Thanks, glad you'll enjoy it :D. After seeing your Airforce-type build, I got to thinking on this arrangement and liked it. Hope you have plenty of popcorn, this may take some time LOL.
Jesse
-
I’m a patient person.
It sounds as though you have three projects going on here. A lathe, a rifle and a pump. So undoubtedly, it will take some time.
What caliber?
Dave
-
Don't have any progress to add on the gun, but am getting there on the lathe:
-
nice ,are you handscraping the entire bed and ways ?
-
That's just a preliminary "practice" scrape on the bed, I still have to grind a center relief to get the plug welds out of the way... I will be scraping in all the sliding surfaces, the dovetails are just filed out at the moment and my filing skills leave a less-than-flat surface. I haven't scraped in anything start to finish yet, was something that I always intended to learn (bought the blueing, a small surface plate, made a HSS bladed scraper etc.) but never had the time to actually learn the art...
Jesse
-
I’d put a foster fitting in it so you could use it like a pcp when you have access to a tank or compressor but still be a acp
-
Update:
Sb327, it's a .22. Want to keep standardized ammo around as my 350 Mag is .22 also.
Blutroop, I will do that. Mainly wanted an on-board pump for independence in the field; I may get a normal PCP handpump for regular shooting.
Have reverted to a standard pump linkage; the design I started looking into in previous sketches looked nice on paper; but I'll be danged if I can figure out a good way to build it.... :P Will just have to settle for a smaller pump bore and a standard linkage; think I can get away with a .62" ID tube. with a 3.25" stroke.
Have a unique thought on valve pinning, using shoulder bolts. 5/32 diameter high-precision shoulder bolts from McMaster are rated at 84 KSI shear, crunch the numbers and you get 1610 lbs single shear. 2 bolts in double shear gives a break strength of 6442 lbs, safety factor with 3000 psi in the tube is a 4.73:1 safety margin. I think I can get away with dual-purposing the bolts to hold a top scope rail/mount and the trigger group bar at the same time. The tube wall looks like it will yield (just barely) before the bolts snap; I will clarify this will only be used for pinning the valve.
Any thoughts?
-
ive done that pinning before , even with a single dowel ( .25 ) going through both sides of the tube.. Yes the math generally says the tube will deform before the pin breaks.. 2 smaller ones does the same trick.. I prefer to do 1 , less work involved.( the one pin is more centered on the tube with the bleed hole offset
-
I actually thought of the idea from seeing your post on another thread; then got to thinking of dual purposing the bolts to hold the other parts on, too.
Jesse
-
idea.. 2 760 pump assemblies side by side .. then , using the factory front valve check valves , it would be easy to thread those to a manifold .. that manifold joins to the plenum.. Youd have double the swept volume , easy plumbing like connections ( the valve fronts are 1/2-20 males) .. super simple .. Pumping will get hard , but thats a good thing.. Link the 2 forearms with one master forearm ( a 2 by 4 with a smiley face )
this could be done with a hacksaw , some home depot fittings, a block of aluminum , a drill press and a few taps.
-
Now you have me interested in 760 pump bodies, did not know the valves were threaded 1/2-20. I have taps and dies covering 4-40 thru 1/2-20 UNC/UNF so fabbing the connector would be easy. Do you know the outer diameter of a 760 tube offhand?
Jesse
You also roughly approximated my tool list.. Have a full 0-6 Starrett micrometer set, 0-12 depth mic, calipers, gauge blocks, test/dial indicators, 9x12 surface plate, lots more.... Just no "machine" tools past a beat-up drill press. Hacksaw, dremel, files, and a couple cold chisels. Ugh. Nice to be able to measure 100x more accurately than you can produce........
-
the tubes are .750 o.d .620 id.
yea, it would be simple.. Even before i had any lathe or mill , I made a contraption similar to this idea with just a drill press and some taps ..
to be clear , i bleieve the 760 threads are an npt thread that 1/2-20 happens to fit perfectly ( 1/4-18NPT or something )
Lets assume all this stuff is figured out , what needs to be built on the front side of the gun?
-
another idea, the 760 tube will eventially need 2 flat top setups.. ( to reach 3000 ) but for a proto , 2 stock arrangments would actually work fine for pumping to 1500 or so.. Maybe some stiffening of the piston rods with nails get you to 2200
-
3000 PSI is not a hard figure. That is the max the setup will ever see; the lower the pressure I can reach my FPE goals at the better.
Hope to get there at 2500 or so; will not know for sure until I try.
Jesse
-
Up front? You mean the action, correct? That will all be from scratch too, I have a good-sized chunk of bearing bronze that I will use for the valve body. 1/2" stainless rod for the poppet, have a stick of 3/8" PEEK for the poppet head. Barrel will either be a Lothar Walther blank, or more likely a sleeved .22LR liner/maybe a sleeved FX liner. Breech slide, hammer and power adjuster will all be out of other tube or rod stock. May order some aluminum rod for the barrel bushing, weight will already be up there. Scope rail and trigger group will come out of random bar stock/plate, grips will be from black walnut I salvaged from some firewood. Haven't figured out too many of the specifics on the power adjuster/hammer etc. Thinking that they will ride on the barrel, I believe that's how they do it with the Condors.
Jesse
-
They ride the inside of receiver tube around the barrel. Same difference.
If you end up with a dual pump, could you design it to drop out one pump when it got too difficult? Then just use one to boost it on up.
How long barrel you planning on using?
Dave
-
I'm not sure about doing dual pumps in the first place; I like slim guns ;). As far as barrel length; as long as possible. The action from the butt up to the rearmost full cross-section of barrel will be around 14", keeping to an OAL of 48" that gives me room for a 34" barrel, or a 28" barrel with a 6" LDC. Don't really want to go longer than 48" overall, and 28" blanks seem to be common (and cheap).
Jesse
-
Dave has a good idea, youd essentially have a 2 stage pump if one could disengage..
I thought you were getting most of the parts from aliexpress and ebay and just making a frame.. Not making every single part.. thats a lot of work ;D
-
Haha-I didn't choose the username JuryRigger for nothing.... ;) Hopeless gotta make it myself lunatic is what I am...(with a healthy dose of penny-pincher thrown in)
The thought of a 2 stage pump is most interesting, if you kept each pump cycle running in a 1-2 fashion, you could gain some efficiency in a sense... Would be even better if you used a larger bore pump for the "first" stage to feed the second precompressed air at an even higher ratio.... Food for thought, will sleep on it.
Jesse
-
Maybe you could keep it slim. Run small stage inside large ram. Lock rams together till pressure gets high. Lock large ram to cylinder, unlock small ram to boost. Small ram only needs connection to arm. In stowed position, both locks on.
Just spitballing....carry on
Dave
-
At one point, I was debating a coaxial 2-stage pump that resembled my second pump design, the difference being the piston rod would be slightly smaller in diameter relative to the pump bore. First stage compression would be accomplished with closing the pump, the air from the full bore area being forced into the smaller volume around the piston rod. Final compression would be from pulling the piston rod outwards, the pump outlet would be by the end of the cylinder.
Think I will stick with simple designs, I already have my work cut out for me.
Jesse