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Custom Aluminum Pneumatic Build

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: velocity3x » Sat May 18, 2013 11:54 pm

gyrotech wrote:
Not sure what HPA is?

HPA = high pressure air
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Unread postAuthor: ramses » Sun May 19, 2013 11:18 am

gyrotech wrote: Generally I did 0.200"-0.300" passes for rough cuts and 0.050" for final cuts.


Even with the boring bar!? It must be nice to have a rigid lathe; I would consider 0.050 roughing for me on my 7x14 (boring). 8 Hours seems perfectly reasonable.
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Unread postAuthor: gyrotech » Mon May 20, 2013 12:29 am

Even with the boring bar!?


Yes quite easily. It is a rougher looking cut but who cares. It's finished with a finer cut afterwards. The key is slower travel speed on those heavy cuts.
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Unread postAuthor: jackssmirkingrevenge » Mon May 20, 2013 12:58 am

gyrotech wrote:The key is slower travel speed on those heavy cuts.


One good rule I definitely picked up was "If a tool chatters, reduce speed and increase feed".

I made a piston out of Acetal but it's pretty heavy. I might make the piston from Aluminum, hollow it out, weld a cap on one end.


A spool type piston is probably a good idea in this case, it saves a heck of a lot of weight bu avoiding large diameters while retaining adequate strength.
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Unread postAuthor: Crna Legija » Mon May 20, 2013 4:17 am

also if your using carbide tools, you need to take a large cut for a good finish 0.5mm at least! and carbid likes to be pushed so a bit more feed than if you were using HSS.
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Unread postAuthor: gyrotech » Mon May 20, 2013 10:28 pm

jackssmirkingrevenge wrote:One good rule I definitely picked up was "If a tool chatters, reduce speed and increase feed".


Agreed.

jackssmirkingrevenge wrote:A spool type piston is probably a good idea in this case, it saves a heck of a lot of weight bu avoiding large diameters while retaining adequate strength.


Not following what you mean by spool type piston?

Crna Legija wrote:also if your using carbide tools, you need to take a large cut for a good finish 0.5mm at least! and carbid likes to be pushed so a bit more feed than if you were using HSS.


Almost all my tooling is carbide :) and yes I agree.
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Unread postAuthor: jackssmirkingrevenge » Mon May 20, 2013 11:56 pm

gyrotech wrote:Not following what you mean by spool type piston


Something like this:

Image

Basically disks on a rod.
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Unread postAuthor: Zeus » Tue May 21, 2013 8:27 am

I wish I had the torque for carbide, and a convenient tool post size :-(

Fantastic work, but it's a shame to see such solid construction being used at low pressure.
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Unread postAuthor: velocity3x » Tue May 21, 2013 3:19 pm

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Unread postAuthor: gyrotech » Wed May 22, 2013 5:51 pm

Zeus wrote:Fantastic work, but it's a shame to see such solid construction being used at low pressure.


I'm unsure how much pressure the unit can take. What do you guys consider high pressure, what do you consider low pressure?
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Unread postAuthor: gyrotech » Wed May 22, 2013 6:36 pm

Got some big heavy welds done and it looks like we have an air tank.

Image

Image

sch80, 4" Aluminum pipe, 54" long. Capped with some 1" thick material, set into the pipe, sticking out 3/8", a root weld and big heavy cap.
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Unread postAuthor: gyrotech » Wed May 22, 2013 6:46 pm

Like So....

Image
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Unread postAuthor: jackssmirkingrevenge » Wed May 22, 2013 11:23 pm

Nice... chamber is probably a little oversized but who cares :D

gyrotech wrote:I'm unsure how much pressure the unit can take. What do you guys consider high pressure, what do you consider low pressure?


Anything up to 150 psi or so is usually considered to be "low" pressure (these days at least, I remember when I got into this hobby 200 psi was off limits, because it will definitely 'splode! lol) depending on how you hook it up though it looks like this will take at least double that safely.
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Unread postAuthor: gyrotech » Thu May 23, 2013 5:28 am

Barrel, 1.75"ID, 7' long: 201 cubic inches
Chamber, 3.875"ID, 54" long: 630 cubic inches

Barrel:Chamber, 201:630 is 1:3.13

Sounds right on the money to me.
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Unread postAuthor: jackssmirkingrevenge » Thu May 23, 2013 7:16 am

Have a play with GGDT: http://www.thehalls-in-bfe.com/GGDT/

I figure that you probably won't see much reduction in performance if you chop the chamber in half, unless you're firing a reallly heavy projectile.
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