Building a Modern Pneumatic Airgun

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JimM:
Great work there Stot, if the rest turns out as well as the parts so far it's going to be a beauty. Will you be making the stock as well or just the mechanicals?

Cheers

Jim
(a HW80K owner)

Stot:

--- Quote from: JimM on November 11, 2010, 03:40:41 PM ---Great work there Stot, if the rest turns out as well as the parts so far it's going to be a beauty. Will you be making the stock as well or just the mechanicals?

Cheers

Jim
(a HW80K owner)

--- End quote ---

Not for these one. I bought 2 stocks of ebay for £9 each posted so if they will work ill use those first. :thumbup:

Cheers
Stot

Stot:
Right next up I made the plugs for the valves. They are threaded brass plugs with a stub to locate the valve spring on, a slot to screw it in and holes for airways.

I started off trying to make them all as one piece then parting off but had a little mishap when I was chamfering the edges for threading and snapped off 3 of them so ended up making them as 2 pairs.
:doh:
There are some milling operations here to cut the slot and drill the holes but I came up with a way to do the lot on the lathe. The holes were easy, use the 4 jaw chuck and mount the parts off center to drill the holes. Other than in future using a center drill to start them this worked well.

The slot however slightly more difficult, you could mount an end mill or slitting saw in the lathe, then mount the part on the cross slide and cut the slot, but I have a Unimat SL, So I made a stand for it out of an old indicator stand and clamped it to my cross slide. Lined up the slitting saw in it with the lathe center line and used the lathe feeds to cut my slot. :borg: I can use this as a toolpost grinder in future too. :ddb:

So below pics showed that I..

* Turned down the brass bar to major thread diameter and cut recesses with my parting tool.
* Chamfered the edges for threading.
* Broke it.. So chucked it up to do just 2 of them./
* Threaded the bar.
* Ground an edge on the bottom of an old hacksaw blade and parted off each one, wasting as little as possible.
* Made the other two the same way.
* Mounted each one in the lathe to face them off and clean them up.
* Set up my Unimat SL head on the cross slide.
* Used an end mill mounted in the chuck to set my slitting saw to center line.
* Cut the slots.
* Changed to the 4 jaw chuck and mounted the part off center for hole drilling.
* Drilled the holes. (I'd use a center drill to start them next time as one slipped)
Other than cleaning up with a needle file thats it. The last picture is the first attempt at these which I wasnt happy with. The slitting saw arbour was slipping in the chuck so they all went off center. Although they would be functional, they arent 'A Game' stuff, so rejected for these rifles. :dremel:

Cheers
Stot

Stot:
Two updates today from the weekend.

First up I made the air inlet valve internals. Very simple one way valves with an o-ring seal. Only bit im not making is the O-Ring. :borg:

So below I,

* Chucked up some stock and turned it to fit inside the valve housing.
* Turned a section to slip inside the through-hole in the valve housing.
* Parted off and flipped it around in the chuck.
* Turned the spring guide end. That part is done.
* Mounted a suitable bar in the lathe to make the size of spring I wanted. pinch the music wire in the chuck and start hand cranking the chuck.
* After a couple of turns to get a spring started, engage the half-nut to set the carriage moving at the spring TPI youre after and turn for desired length of spring. Disengage half-nut and finish the spring with a couple of turns.
* Clean the springs up and all parts ready for assembley.

Tested these and they hold 30bar pressure overnight so at the moment, jobs a goodun. :beer:

Cheers
Stot

Stot:
Ok so part 2-2, the Poppet valve internals.

I am veering slightly from the book valve design that uses a flat seated valve. I am going to use a tapered valve seat and seal which I feel has better redundancy in the design, and has better air flow characteristics.

So,

* Cut the valve seat into the valve body.
* Chucked up some Delrin to make the valve seal.
* Drilled a hole to thread onto the valve stem.
* Parted off using a 60 degree tool bit.
* 2 valve seals.
* Chucked up some bar to cut the valve stem. This is a bit big, but I had it around so it will do. :D
* Turned it down to a 'go' fit to the valve housing then polished it up.
* Turned down to make a thread for the seal to go on. Threaded.
* Parted off and mounted in the chuck again.
* Threaded the Delrin seal onto the rod.
* Cleaned up the seal face and cut the spring guide onto the back of it.
* Assembled the valve with a spring made the same as the one above.

Filled to 70bar overnight just to see it held pressure. No problems. :headbang:

Cheers
Stot

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