Introduction and My First Pneumatic

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
User avatar
hectmarr
Corporal 3
Corporal 3
Posts: 755
Joined: Sat May 07, 2016 3:49 pm
Location: Yaren
Has thanked: 1 time
Been thanked: 1 time

Wed Nov 06, 2019 9:11 am

I have this drawing of a pressure regulator to share.
Attachments
pressure regulator.jpg
Ideas don't make holes, guns do!
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 25658
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 20 times
Been thanked: 8 times

Donating Members

Wed Nov 06, 2019 9:34 am

SloppyJoeES wrote:Chicken :wink: :bom:
Far from it, Moonbogg is just acutely aware of potential material failures and their negative consequences, and on this forum definitely the one who goes the furthest to make sure nothing is left to chance, which is laudable in my book.
hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
mrfoo
Specialist
Specialist
Afghanistan
Posts: 147
Joined: Wed Apr 29, 2015 11:05 am
Has thanked: 3 times
Been thanked: 4 times

Wed Nov 06, 2019 3:19 pm

Any ideas for removing those damn screws? They're in there good!
The trick I use for removing recalcitrant and buggered allen screws is:

Take a drill-driver bit of the correct size, put it in the remains of the hole. Using a pin punch, carefully peen the remains of the head around the driver bit, thus re-forming the hex. Then, without removing the bit, hit it with your drill driver on maximum torque. This approach is very effective on small steel bolts (m5, m6) corroded into alu, as the act of peening over "shocks" the threads free , more or less. Throw away the bolt once you've done, obvs.

Not sure if this will work on screws you've simply over-torqued.
User avatar
Moonbogg
Staff Sergeant
Staff Sergeant
Posts: 1550
Joined: Mon Oct 13, 2008 10:20 pm
Location: SoCal
Has thanked: 9 times
Been thanked: 2 times

Wed Nov 06, 2019 6:53 pm

jackssmirkingrevenge wrote:
SloppyJoeES wrote:Chicken :wink: :bom:
Far from it, Moonbogg is just acutely aware of potential material failures and their negative consequences, and on this forum definitely the one who goes the furthest to make sure nothing is left to chance, which is laudable in my book.
I do the best I can, but also my nano-suit went missing so I have to protect my frail human form using preventative measures instead.
User avatar
D_Hall
Staff Sergeant 4
Staff Sergeant 4
Posts: 1870
Joined: Thu Feb 07, 2008 7:37 pm
Location: SoCal
Been thanked: 3 times
Contact:

Donating Members

Sat Nov 09, 2019 11:51 am

jackssmirkingrevenge wrote:Most commercial pneumatic air rifles operate in the 2000-3000 psi range, nothing wrong with higher pressures as long as they are safely contained. In a QEV designed for 150 psi though, it is bordering on suicidal.
Fixed that post for ya.
Simulation geek (GGDT / HGDT) and designer of Vera.
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 25658
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 20 times
Been thanked: 8 times

Donating Members

Thu Nov 14, 2019 7:33 am

D_Hall wrote:Fixed that post for ya.
Eh, teen subculture these days seems to be all about that, at least they're being creative about it.
hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
SloppyJoeES
Private
Private
United States of America
Posts: 11
Joined: Thu Jun 20, 2019 6:34 pm
Location: Chico, California

Sun Nov 17, 2019 9:04 pm

Although taking fittings outside their ratings, especially to such an extreme degree, is inherently dangerous, I don't see this is particularly suicidal. I am well outside the burst pressure for any component and the only thing I can see getting easily destroyed is the diaphragm in the QEV, which would simply cause a constant stream of hpa tank to come through the batrel until the hpa ran out or I turned it off, and fire whatever projectile may have been in the barrel I'm the process.

Not condoning this kind of behavior, but I don't see that huge of a risk to my own health taking place here, so much as I place as much respect on the launcher as I might a firearm.

Anyway, I am indeed switching to something a little less crazy, which will output 450psi. Until the parts that will allow me to do that come in however, I have finally decided to make my own clone of one of my favorite projects on the site, jack's pen gun.

Its going into a 8mm od 6mm ID tube made of 304 stainless steel. The barrel will be a 1/8" annealed aluminum tube made by K&S I got from Ace. I plan on moulding a piston out of hot glue, onto which I will adhere a 3/16" thick piece of gasket rubber to be the sealing face.

I say 'adhere' because I have no idea how to stick this thing in best... I already tried making one of these in a 1/4" pipe nipple with a piece of 1/4 copper tubing as a barrel and the same piston setup described above, but with the rubber glued on with superglue. The superglue made the rubber kind of stuff, so I thought maybe that's why it won't seal well. I also have guessed that there may have been an issue using threaded pipe fittings as the chamber, as the threads may have interfered with the seal, but honestly I have no idea. This projects got me feeling DUMB so far...

My new one will be done with a lot more care, so hopefully I am more successful. Any advise on my piston and how to make the pen gun work properly? I understand how it works fine.
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 25658
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 20 times
Been thanked: 8 times

Donating Members

Mon Nov 18, 2019 7:19 am

SloppyJoeES wrote:Although taking fittings outside their ratings, especially to such an extreme degree, is inherently dangerous, I don't see this is particularly suicidal. I am well outside the burst pressure for any component and the only thing I can see getting easily destroyed is the diaphragm in the QEV, which would simply cause a constant stream of hpa tank to come through the batrel until the hpa ran out or I turned it off, and fire whatever projectile may have been in the barrel I'm the process.
The assumption you're making here is that there isn't some flaw in the components that would reduce the actual burst pressure, it's important to be aware of the risks especially with parts manufactured to a price.
SloppyJoeES wrote:I plan on moulding a piston out of hot glue, onto which I will adhere a 3/16" thick piece of gasket rubber to be the sealing face.
Hot glue is a bad idea if you plan on taking it to significant pressure. Consider epoxy instead.
hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
SloppyJoeES
Private
Private
United States of America
Posts: 11
Joined: Thu Jun 20, 2019 6:34 pm
Location: Chico, California

Tue Nov 19, 2019 10:35 pm

I have had great difficulty casting a piston for the pen gun. My problems mainly arise with pouring and removing the materials I have tried so far. I was only able to remove my hot glue piston once. The second time, I tried to remove the hot glue from the pipe section I casted it in and it was stuck with no hope of getting it out without destroying it.

I have also used JB Weld, both on its own and mixed with a minute amount of acetone to water it down.

Each time I used vegetable oil and Pam to try and keep the stuff from sticking. At this point, I almost feel like giving up or trying something larger. Maybe a thick rubber sheet cut to size would work well instead.
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 25658
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 20 times
Been thanked: 8 times

Donating Members

Wed Nov 20, 2019 7:05 am

SloppyJoeES wrote:Maybe a thick rubber sheet cut to size would work well instead.
I can confirm that it works. For casting you really need the right materials and I find that marine epoxy works best as per the guide posted previously.
hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
SloppyJoeES
Private
Private
United States of America
Posts: 11
Joined: Thu Jun 20, 2019 6:34 pm
Location: Chico, California

Thu Nov 21, 2019 10:14 pm

I got my hands on a nice 1/4" thick piece of rubber. Now, my issue is cutting my piston out of it. I first tried to punch out a cylinder of it by merely pushing a segment of my chamber tubing into the rubber until it came through the other side.

I placed my chamber perpendicular to the rubber sheet in the vise, and tightened it until the pipe cut out some of the rubber. The rubber piece I got from this method did not turn out super well, looks more like a diabolo pellet with a flat head than anything else. Definitely not the cylinder I wanted to see.

I then got my file and some sandpaper: 180 grit and 120, and tried my best to sharpen the end of the tube. I worked for about 30 min sharpening the tube with the file, while it sat in the jaws of my vice. It was extremely time consuming for how dull this thing is. Definitely a hell of a lot sharper than before but still a long ways off. I cut the rubber using the same method as before, and all my effort was rewarded with a slightly easier time tightening the vise. The rubber piece that I ended up with ended up looking basically identical.

I do not currently have a drill or any other power tools to use for sharpening my pipe. I could try to borrow one from my parents back home, or my girlfriends parents, but I don't see either happening. Nobody is supportive of anything I have tried to make based on this site lol; maybe for good reason.

I could continue to sharpen my tube my hand with the file and sandpaper, but I must say I am quite discouraged considering that even though it was much easier to cut through the rubber after I sharpened it, the rubber piece I ended up with was functionally identical.

Any ideas on where to carry on from here? Right now my options seem to be: sharpen pipe more by hand, wait for a considerable time to try and get power tools to make my time sharpening the pipe easier, try to cut out a portion of rubber with a knife.

All have some significant shortcomings.

Any ideas?

Picture:
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 25658
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 20 times
Been thanked: 8 times

Donating Members

Fri Nov 22, 2019 9:11 am

SloppyJoeES wrote:Any ideas on where to carry on from here? Right now my options seem to be: sharpen pipe more by hand, wait for a considerable time to try and get power tools to make my time sharpening the pipe easier, try to cut out a portion of rubber with a knife.
A power drill is less than $25 from home depot and it would solve all your problems, you just chuck a section of chamber material in the drill and sharpen the outside with a file.
hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
SloppyJoeES
Private
Private
United States of America
Posts: 11
Joined: Thu Jun 20, 2019 6:34 pm
Location: Chico, California

Sun Nov 24, 2019 4:45 pm

I sprang for a drill at walmart, as it was even cheaper. I had always assumed they were more expensive than this... 16 dollars for a cordless drill. Not like it seems to work well enough. Popped it in the vise, gave sharpening my tube a go. Got a pretty steep edge on the whole thing. Not terribly sharp yet, but definitely a lot sharper. I tried cutting out some pieces by hand and got a lot farther than before, but I still had issues, so I turned to my new drill. used the drill and punched out a couple tubes of rubber. They are definitely not a perfect fit still though (see attached picture). my assumption is that I should not be able to see light shining around the sides. The piston fits pretty snugly though, and will move back and forth by blowing and sucking air through the tube.

After I didnt get absolutely perfect results with the drill, I used the vise method again and promptly crushed my brand new edge. Oh well... I will get to sharpening it again or maybe just start on a new piece of tubing.

My question now, if someone does not mind answering, is: will this piston work, or should it be much tighter in the tube?

I already finished a pen gun, using a bic pencil eraser that was quite hard though still soft enough to seal partially against the barrel with only the pressure of my own breath. The fit was pretty much perfect, quite tight but could be pushed easily enough. It did not work though all said and done. Maybe the barrel was not perfectly centered.

Pictures:
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 25658
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 20 times
Been thanked: 8 times

Donating Members

Mon Nov 25, 2019 8:36 am

Image

Far too loose to work well.

When you sharpen your tube, be careful as you tend to bend the edge of the tube inwards, resulting in a smaller diameter piston.

You can use a mandrel to center your barrel, like a rod the same diameter as you inner diameter of your piston wrapped in tape until the diameter of the tap is the same as the inner diameter as your chamber.
hectmarr wrote:You have to make many weapons, because this field is long and short life
Post Reply