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Old 11-06-2017, 10:54 AM   #11 (permalink)
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Rawbutter, sounds like you need a machinist to take this to the next level. Plexi was fine for your proof of concept, but you'll want to move to brass. You're never shooting blind if you've done your measurements right, brass will hold higher pressures, machines nicer, holds better tolerances. Passages should be drilled undersized then reamed to spec to ensure accuracy and surface finish. Designing for proper tolerances and oring crush will give your pistons smoother travel with minimal friction. All easier said than done, but that's why these guys above me are the pros
I agree, but part of the reason I'm doing this project is to learn more about machining. I bought a mill over the summer, and this is teaching me a lot about my equipment. If a machinist wants to borrow this idea and run with it, however, they are welcome. All I ask if that you give me one of the prototypes.


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Originally Posted by tymcneer
Plexiglass can be chemically polished with acetone. Use it on a spare piece to perfect your technique.
Hmm....I'm not sure I'm comfortable working with chemicals yet. And the valve does kinda work, so maybe it's time to move on to a different material.

What about polishing brass? I have been underboring the holes with a 15/64 bit before reaming out to 1/4". What should I do after that? Boring brush?
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Old 11-06-2017, 11:02 AM   #12 (permalink)
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Also, is there a different kind of o-ring I should be thinking about? The o-rings I'm using are from a local hardware store, and they're nothing special. Probably Buna. I can order something else online, obviously, but I'm not sure what kind is best for something like this.
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Old 11-06-2017, 11:52 AM   #13 (permalink)
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Originally Posted by rawbutter View Post
...snip...
Hmm....I'm not sure I'm comfortable working with chemicals yet. And the valve does kinda work, so maybe it's time to move on to a different material.

What about polishing brass? I have been underboring the holes with a 15/64 bit before reaming out to 1/4". What should I do after that? Boring brush?
Acetone is nail polish remover. Flammable and not a good idea to use in an enclosed space, but mostly harmless.

The finish you want can be made using a reamer. Drill the hole about 0.010" undersized, then switch from a drill to a reamer, without moving the material you are working. This will allow the reamer to be axially in line with the hole, and produce a very good finish. Use oil, and lower the RPMs, as reamers don't want o be run fast (high surface feet per minute)

If you'd like some help, PM me.

Ty
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Old 11-06-2017, 12:08 PM   #14 (permalink)
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Use oil, and lower the RPMs, as reamers don't want o be run fast (high surface feet per minute)

If you'd like some help, PM me.

Ty
Okay.... that helps. I did switch from the drill bit to the reamer without moving anything else, so I did that part right. But I did not use oil when reaming, and I was running my mill at the highest RPMs. Whoops. I'll try again.
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Old 11-06-2017, 01:52 PM   #15 (permalink)
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Reamer+dry+hi-rpms would definitely be an issue. You were probably melting the plexi.

Very cool you've obtained a mill, carry on with the learning!
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Old 11-09-2017, 05:35 PM   #16 (permalink)
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okay, I ran out of Plexiglas, and my brass hasn't shown up yet, so I made the third prototype out of aluminum.

On the plus side, the aluminum isn't cracking or wearing out like the Plexiglas. I'm getting good seals, no leaks, and a strong pulse (although I think I need over 100 psi into the valve to fire a marker). After polishing the inside of the valve, the o-rings slide much better now. Still not super light, but lighter than a standard mechanical marker for sure.

Unfortunately, now I'm having a super-slow recharge problem, which doesn't make a whole lot of sense to me. The air reservoir should refill near-instantly, but if I rapid fire the valve, there isn't enough pressure to trip the sear. Also, if I pull the trigger slowly, nothing happens whatsoever.....which is very odd. I had assumed that the pulse valve would fire no matter what speed I pulled the trigger. That was half the reason I wanted to make on in the first place.

http://www.youtube.com/watch?v=DUPUUi08d2E

So, onto prototype #4. At least I'm getting pretty good at making these.

Last edited by rawbutter; 11-09-2017 at 05:46 PM.
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Old 11-09-2017, 05:47 PM   #17 (permalink)
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Also, if I pull the trigger slowly, nothing happens whatsoever.....which is very odd. I had assumed that the pulse valve would fire no matter what speed I pulled the trigger.
That just sounds like a leak from the reservoir or through the piston or tuning screw, which is overcome with a faster cycle.

On faster cycles, could you be shorting your reservoir recharge by not letting the trigger rod out far enough?
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Old 11-10-2017, 10:19 AM   #18 (permalink)
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On faster cycles, could you be shorting your reservoir recharge by not letting the trigger rod out far enough?
Good idea. I tried letting out the set screw in the trigger (which limits forward travel from the trigger rod), and that helped. I can fire faster now. The pulse isn't as short, though. The Synergy fires two or three shots before the valve resets. So.......maybe I need a smaller reservoir?
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Old 11-10-2017, 03:07 PM   #19 (permalink)
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That just sounds like a leak from the reservoir or through the piston or tuning screw, which is overcome with a faster cycle.
I was intentionally leaving the tuning screw unsealed. If I seal it, then air will get trapped between the last o-ring and that screw, creating a situation where the trigger rod won't move anymore (because I'd be trying to compress air with nothing but my finger).

But I can try it the other way. The air hole that connects the main center tube to the piston channel is pretty wide. Air might leak past the o-ring and fire the piston before the o-ring seals up the end.
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Old 11-10-2017, 06:38 PM   #20 (permalink)
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I didn't mean that the screw should be sealed, but that the oring next to it may be losing the pressure, with the air passing by the screw.

The dwell time of the pulse is a function of the reservoir size and the vent size. For shorter dwell, a smaller reservoir or larger vent works. For experimental purposes, it would be nice to have a piston that you could turn in to adjust the volume. Or just throw some washers in your existing one to devolumize.
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