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Hammer valve-->Piston

Posted: Thu Mar 02, 2023 6:04 pm
by Pennywise
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.

Re: Hammer valve-->Piston

Posted: Fri Mar 03, 2023 12:22 pm
by mrfoo
Nice machine, and nice result.

For hydrotesting, cheap hand actuated grease guns generally go up to about 400 bar, used one for some hydroforming experiments a while back. The hardest bit is fittings, and managing to get a gauge in circuit.

Re: Hammer valve-->Piston

Posted: Mon Mar 06, 2023 12:49 pm
by Pennywise
So when attempting this with the grease gun, do you just fill the system and grease gun with as much water as possible, then attempt to continue pushing more water in?

Re: Hammer valve-->Piston

Posted: Tue Mar 07, 2023 8:58 am
by mrfoo
You need the entire system to be filled with water, or as close as you can get to that. Then connect the grease gun and pump grease in. Doesn't matter that it's not water, or that it's not miscible, all you need is something incompressible. Tear down and clean up afterwards.

Re: Hammer valve-->Piston

Posted: Wed Mar 08, 2023 10:03 pm
by Moonbogg
I like the machine work you did. I love projects like this. I did the grease gun thing like mrfoo said, and it worked for me. I filled the cannon with water, then pumped grease in. I've read that you can modify the grease gun to pump water in, but all that did was leak for me. There's a way to do it though. I think you reverse the seal inside the grease gun and it becomes water tight or something. Cleaning that grease was a huge pain in the ass, so if you can avoid that I'd suggest it. I only went to 450psi to test a spud gun.

Re: Hammer valve-->Piston

Posted: Wed Mar 08, 2023 11:50 pm
by Gippeto
Nice lathe. 8-)

Porta power gets my vote...oil is easier to clean up than grease. Testing a pcp reservoir.


Re: Hammer valve-->Piston

Posted: Mon Mar 13, 2023 10:03 am
by jackssmirkingrevenge
Absolutely beautiful they-don't-make-'em-like-they-used-to lathe and great work you've done with it! I look forward to some higher pressure testing :D

Did I understand correctly that you have a metal-on-metal seal for the piston seat?

Re: Hammer valve-->Piston

Posted: Tue Mar 14, 2023 10:15 pm
by Pennywise
Im highly considering paying for the history of my machine. Monarch will sell information about then original purchase (price, accessories, etc) as well as where it was shipped to.

Yes, the hammer seat and piston seat are both brass-on-steel. Appreciate the compliments, guys. Right now I'm building a follow rest for the lathe, then I should be able to get back on track.

Re: Hammer valve-->Piston

Posted: Sat Mar 18, 2023 9:04 am
by jackssmirkingrevenge
Pennywise wrote:
Tue Mar 14, 2023 10:15 pm
Right now I'm building a follow rest for the lathe, then I should be able to get back on track.
Sometimes building tools and jigs is half the fun :D

Re: Hammer valve-->Piston

Posted: Sat Mar 18, 2023 2:08 pm
by mrfoo
jackssmirkingrevenge wrote:
Sat Mar 18, 2023 9:04 am
Sometimes building tools and jigs is half the fun :D
And the other half is doing it again when you realise you've buggered something up :)