Phase 1: COMPLETE!! (It works)

Ok, quite a bit has happened since last time.

1. I built the ball check valve.

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The operation’s were pretty simple, just a bunch of drilling on the mill.

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Here it is all buttoned up.

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2. I cut out and attached the bumper.

The cutting out part turned out to be very difficult. The rubber I used is soft, but tough and scissor resistant. I eventually got it cut, but the edge looked awful. It was usable, but I wanted to do better.

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I tried a bandsaw (it just gummed up immediately). I tried lubricating the blade and sandwiching the the rubber with wood; that helped, but still left a nasty looking edge. I ordered and tried a razor saw but that didn’t work very well either. I was getting pretty stuck.

I started asking my friends at work about it. First response: “Aren’t you fixing a trim press right now that’s designed pretty much exactly for that?”  …I probably should have thought of that. Anyway, I was, it it was the perfect tool for this. This is it:

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As it happened, I just got it working.

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I made a quick die out of 3″ pvc pipe.

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The press has a low power height-set mode. Unfortunately even that was too much for my die.

I tried again, this time I put the ring in the press before sanding down the cutting edge. It survived this time.

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The edge quality came out great this time. (I cut out the center hole with the press as well). The disk is now smaller than the pipe ID, but that may be a good thing, since this’ll give it room to deform and soften the impact.

Lastly, I glued the bumper to the back plate with the loctite #380.  I forgot about the smaller ID and put some extra around the edge. I’ll have to sand that off later. No biggie though.
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After applying the glue I clamped the assembly between some boards and left it for 24 hours.

3. ASSEMBLY.  ..After 60 or more hours of machining and designing, I couldn’t wait to test it out.

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It’s very awkward to hold with no stock (that’s phase 2), but I did a couple of test shots.

It’s working pretty awesome. I noticed a few things in testing though. The length of the piston needs tweaking, it’s not moving all the way back, which means I could make it longer (and therefor faster) without any downsides. The other thing it the QEV. It’s VERY sensitive. During testing I accidently set off the cannon a few times by removing the schrader valve too slowly. I added an inline check valve after the schrader (you can see it in the above pic) to solve that problem.

I’m happy with the performance for now. I’ll save any further tweaking for after phase 2, when the cannon is less awkward to take out and shoot.