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[New here] First pneumatic gun to start the SpudLife

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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[New here] First pneumatic gun to start the SpudLife

Unread postAuthor: Pete » Mon Dec 27, 2010 1:00 pm

Hi!
I'm new to this forum and I want to introduce myself. I'm 19 years old and I'm from Germany. I experienced the first pneumatic guns at youtube and since then I want to built my own. My first gun should be like the one shown by MrRedRooster, MRR in this forum.

So today I went shopping and buyed this:
Image

It's all very basic and all I buyed is with a thread, so I can easily connect the parts. After I went shopping, my dad said that he has tons of this parts, so I can get money back for most of the parts. I've also found a manometer in his chests, so this thing is goint to rock.

It should end up like this:
Image

The piston will be hotglue with a bumper. The chamber is a 1,25" tube, 12" long. The barrel is 0,5" and 32" long.

So that's it. I will build the next day(s) and I hope I can show you something that works.

Greetings,
Pete

Edited by jrrdw, fixed pictures.
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Unread postAuthor: Technician1002 » Mon Dec 27, 2010 1:16 pm

Nice start. Some here will mention the pilot volume is too large.

Be sure to polish the inside of the pipe the piston slides inside. Otherwise it may stick too much and not seal very well.

Made from iron, you should have little problems with it breaking. Your only possible difficulties may be getting the piston to work properly.

Welcome to Spudfiles.
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Last edited by Technician1002 on Mon Dec 27, 2010 8:25 pm, edited 1 time in total.
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Unread postAuthor: Pete » Mon Dec 27, 2010 1:39 pm

Pilot volume means, that the air which goes out to pull the piston will be to much? What do you mean, how can I solve this or is it ok for starting?

So the piston is the difficultiest part on the gun? But I will polish it properly with sandpaper and grease it, so there will be no problem.

@used iron
I thought why use copper or brass, if there is iron, which is much cheaper and stronger.

I'm really curious about tomorrow =)
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Unread postAuthor: Technician1002 » Mon Dec 27, 2010 1:49 pm

The very large air chamber behind the piston is the pilot. The amount of air you have to release to open the piston is excessive.

Look at the amount of air space behind the piston on my Mouse Musket. Only a small amount of air needs vented to fire it.
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Unread postAuthor: Pete » Mon Dec 27, 2010 2:43 pm

The design is like this: http://www.youtube.com/watch?v=apSA_ny8 ... rofilepage
And I thought before I start with something own, I take a working design that is easy to build.
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Unread postAuthor: saefroch » Mon Dec 27, 2010 3:25 pm

That design certainly does work, but a smaller pilot volume will let the valve open with less of a pressure drop in the chamber. If the pilot volume is too large, the piston valve will not pilot at all. It is possible that this setup may have that problem. To fix that, try a layout like this that I used. By putting a ball valve on either side of the place you're filling from, you can get the pilot valve closer to the piston. You could put a ball valve right after the adapting connector and really reduce pilot volume.

Other than that, it looks like it will work, and as Technician1002 says, polish the pipe the piston slides inside, since those pipes are probably rough and have a weld down the inside, no?
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Unread postAuthor: Pete » Mon Dec 27, 2010 4:53 pm

Thanks saefroch ;)
Switching the ball valve and the shrader valve isn't such a problem, I will try it ;)
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Unread postAuthor: MRR » Mon Dec 27, 2010 5:27 pm

Looks all good so far, except the things the others pointed out.

You should also get rid of the 1/2" steel pipe, those are junk (massive welding seam inside) and replace it with 1m by 18mm copper pipe. As ammo I suggest marbles from a 1€ shop (2€ per 100) which have a nearly perfect fit.

You should also consider to replace the nipple, in which the piston slides, with a brass fitting (much smoother surface inside).

And the last thing is, when you work with a hot glue piston you should stay away from mineral oil based lubricants. The hot glue will dissolve and becomes sticky. A good substitute for example is vaseline.

Welcome to the forum.
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Unread postAuthor: Pete » Mon Dec 27, 2010 6:28 pm

@MRR Ok if I change the position of the ball valve with the fill valve, then the design should be like your "Big Boy" gun except from the size. Right?

We have copper pipe at home, but how did you attach it to the system. I am able to cut threads, but isn't it a weird size for my parts?
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Unread postAuthor: metalmeltr » Mon Dec 27, 2010 10:00 pm

You can buy an adapter at the same store you bought these parts to connect it to the threads. They solder on typically.
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Unread postAuthor: MRR » Tue Dec 28, 2010 1:56 am

Yes that would be the like the design I used with the BigBoy.

Image

You can't see it on the picture but there is a compressor quick connect (male) at the end of the 45° fitting. I used to hook it up to compressor, fill the gun, close the valve and disconnect. It is also easy to build an adapter for use with a bike pump.

Image


To connect the copper pipe there are two options:
1. solder fittings
2. compression fittings which come very handy if you are not familiar with soldering.
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Unread postAuthor: metalmeltr » Tue Dec 28, 2010 10:46 am

There is another option Push connect fittings I don’t know if they are sold in Germany but if you can't or don't know how to solder they are an alternative option.
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Unread postAuthor: The_Guerilla_Guy » Fri Dec 31, 2010 4:48 am

Ahh, another guy from Germany, nice ;)

I also bought a 1/2" steel pipe with threads for my last gun, not realising before getting home that they have a seam inside, which makes it nearly worthless :(

Nice gun anyways, be sure to post some videos ;)

@metalmeltr: Those fittings are sold over here as well, but they cost a ******* fortune. I think I saw one lately for about 15 €, which is even more than the 5 to 7 € that you spend on a noirmal (lol typo but I like this ;) they are not black sadly ;)) fitting.

I found that a 15mm copperpipe fits very well in those 1/2" pipes, so i thought about sanding down the inside ot those and use leadfilled 15mm pipe as ammo. just an idea though.
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Unread postAuthor: Technician1002 » Fri Dec 31, 2010 1:27 pm

The seam in the pipe can be fixed. Using a proper size dowel and some sandpaper, the ridge can be removed.

Image

When done, you have a very nice cylinder for the piston. For example, here is a 1 inch valve made with galvanized pipe with a seam.

Here is a peek inside my 2 inch QDV valve.
Image
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Unread postAuthor: MRR » Fri Dec 31, 2010 2:02 pm

Tech, you must be a very patient man. :)
How long did it take you to remove the the seam?
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