Hammer valve-->Piston
Posted: Thu Mar 02, 2023 6:04 pm
I have wanted a lathe since I understood their capabilities. Late last year I finally bought one. A Monarch 10ee, that happened to be born some 3 months before my grandfather (4, 1942). After some careful (read 'creative') planning, and stressful (read 'careful') execution, a friend and I managed to get her into my basement shop. 3500lbs of American glory.
After building a Rotary Phase Converter to actually run the lathe, I decided that a fun first project would be a pneumatic gun to test myself. I've built many in my time, but never past around 500psi.
The cylinder is turned out of 1.5"OD 303 stainless tubing, and the pressure area has a final thickness of ~.13" (The mechanism is together currently, my notes are elsewhere, and I don't feel like finding the exact number right now.) giving ample strength for 4500psi.
The hammer valve pin is made of a hardened tool steel I had laying around, and the sealing face is machined out of brass. The hammer valve body is machined from solid 303SS, is sealed with 3 orings, and is held in place by 4 5/16x24 bolts, as well as a 'step-down' machined into the cylinder housing.
There is a spring between the brass sealing face and the open end of a 'toolies'-esque piston design. This causes pressure on both sealing faces. There is a recessed area at the back of the piston (again, made of 303SS (not pictured is a 1/8"rubber bumper affixed to the rear of the piston)), which is almost perfectly filled by the brass sealing cap when the spring is fully compressed. Threaded onto the front of the piston is another turned brass sealing face, which mates to the very polished surface of the cap (guess what that's made of), which is again held in by 4 5/16x24 bolts, and sealed with orings.
The barrel is a piece of .50"SS, which has had its bore highly polished.
The exhaust port is drilled through the hammer valve housing. the intake is partially drilled into the same housing (though not fully into the cavity, then meets with a 1/16" hole drilled right next to the sealing face of the hammer-pin.
Sorry for my lack of pictures. I didn't think to take many while I was constructing. Soon enough, i'll take it apart again, and i'll try to get more.
Next up is designing and building the hammer system to actually fire the gun. I have some 1000psi videos of tests done, but no real shots yet, as the gun is obviously not nearly complete. My plan is to affix another stainless tube under the existing one, and run a double hammer system. The secondary hammer will be longer, and in the lower cylinder, further away from the rear of the gun so shoulder-mount is a more natural position. The main hammer will link to the secondary hammer (the one in the primary cylinder) via a pin with a slot machined in one of the hammers to allow a bit of 'free movement' prior to engagement. This likely sounds overly complex, or doesn't make sense at all, but I want a reliable enclosed system here.
The barrel has been designed to pull out of the breech for loading. It will ride on polished bushings and will turn out of its lock, slide forward, be loaded, and locked back home again.
I am unable to add any video of the testing (air burst only), but have tested to 1200psi so far. I will not be fully pressurizing the gun until I have devised a method of hydrotesting to a safety margin. After that, this will be ergonomically a rifle when complete.
I expect good things from this, as the only projectile I have fired (sloppily, mind you) was a 1/2" ball bearing. The actual ID of the barrel is something closer to .508, and even with several thou of clearance around the bearing, 500psi still pushed it over 500fps.
*edit; In a resting position, the rear of the piston only sits .3" away from the hammer valve housing, despite the misleading photo. So the entire system moves very little during the action.
The hammer valve pin is made of a hardened tool steel I had laying around, and the sealing face is machined out of brass. The hammer valve body is machined from solid 303SS, is sealed with 3 orings, and is held in place by 4 5/16x24 bolts, as well as a 'step-down' machined into the cylinder housing.
There is a spring between the brass sealing face and the open end of a 'toolies'-esque piston design. This causes pressure on both sealing faces. There is a recessed area at the back of the piston (again, made of 303SS (not pictured is a 1/8"rubber bumper affixed to the rear of the piston)), which is almost perfectly filled by the brass sealing cap when the spring is fully compressed. Threaded onto the front of the piston is another turned brass sealing face, which mates to the very polished surface of the cap (guess what that's made of), which is again held in by 4 5/16x24 bolts, and sealed with orings.
The barrel is a piece of .50"SS, which has had its bore highly polished.
The exhaust port is drilled through the hammer valve housing. the intake is partially drilled into the same housing (though not fully into the cavity, then meets with a 1/16" hole drilled right next to the sealing face of the hammer-pin.
Sorry for my lack of pictures. I didn't think to take many while I was constructing. Soon enough, i'll take it apart again, and i'll try to get more.
Next up is designing and building the hammer system to actually fire the gun. I have some 1000psi videos of tests done, but no real shots yet, as the gun is obviously not nearly complete. My plan is to affix another stainless tube under the existing one, and run a double hammer system. The secondary hammer will be longer, and in the lower cylinder, further away from the rear of the gun so shoulder-mount is a more natural position. The main hammer will link to the secondary hammer (the one in the primary cylinder) via a pin with a slot machined in one of the hammers to allow a bit of 'free movement' prior to engagement. This likely sounds overly complex, or doesn't make sense at all, but I want a reliable enclosed system here.
I am unable to add any video of the testing (air burst only), but have tested to 1200psi so far. I will not be fully pressurizing the gun until I have devised a method of hydrotesting to a safety margin. After that, this will be ergonomically a rifle when complete.
I expect good things from this, as the only projectile I have fired (sloppily, mind you) was a 1/2" ball bearing. The actual ID of the barrel is something closer to .508, and even with several thou of clearance around the bearing, 500psi still pushed it over 500fps.
*edit; In a resting position, the rear of the piston only sits .3" away from the hammer valve housing, despite the misleading photo. So the entire system moves very little during the action.
