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Pete Zaria's Over/Under Combustion

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Pete Zaria's Over/Under Combustion

Unread postAuthor: Pete Zaria » Sat Jan 13, 2007 4:32 am

This thread documents the design and build process of this gun. To skip ahead and see the final product, click here: http://www.spudfiles.com/forums/viewtop ... 666&#57666

Here’s the spudgun I’ve been designing for awhile.

I've posted various threads about bits and pieces of it. I intend to document (with pictures) the build process, and post destruction pics and hang time test results when it's finished.

It’s an over/under combustion made of cellular core ABS. I’ve pressure tested most of these components (not these exact ones, but identical ones [same manufacturer]) to 100psi and I feel safe using them in a combustion. Also, the failure characteristics of ABS are much cleaner than those of PVC – AKA less shrapnel.

My objectives for this cannon were to make it:
Over/under, obviously
Breech loading (no more ramrod’ing potatoes down the barrel!)
Ball-valve vented (no more removing a cleanout between shots!)
Built cleaner and more professionally (No duct tape/rats nests of wires)
Safer (Only holes in the combustion chamber are where a pipe and fitting overlap)
More reliable (Stun gun and spark strip ignition, in addition to the usual propane meter)
More user friendly (recoil pad, better grips)
As lightweight as possible (failing here if anywhere….)

I wanted to use a 2” ball valve for venting, but had a 1.5” laying around, and decided to save the $15. This cannon is built largely from spare parts and parts robbed from old cannons (Don’t worry, I didn’t unglue any fittings to salvage them).

The combustion chamber is 20" and roughly 250ci. This provides a 1.25:1 ratio for a 10' golf ball barrel (coming soon :D). Should be nice and loud with shorter barrels, too.

The recoil pad will consist of a big piece of black foam rubber zip-tied to the U bend (back end) of the gun.

The spark strip is still a work in progress. It's a piece of copper-clad circuit board with 4, 1/8" spark gaps, mounted vertically in a piece of 1.5" pipe cut lengthwise, which will be glued (with non-permanent glue) to the inside of the chamber.

The cannon is currently dry-fitted together (no pieces glued) for two reasons:
A) I want to get your opinions about it before I glue it and make it permanent
B) I have to wait until it warms up. ABS glue and krylon paint don’t work well at 25 degrees Fahrenheit.

Here are the plans I originally intended to work from:
Image
However, I already had a few parts, so I varied a bit from the plans.

Here are pictures of the cannon, with parts separated and dry-fitted, and pics of the “donor gun” I’m taking the propane meter and handles from.


New over/under gun, parts exploded view:

Image

Image

Image

The 4”-2” reducer that connects the ball valve to the chamber will not be glued; it will be attached with bolts. See notes below.

Close-up of barrel put together:
Image

Barrel exploded view:
Image

Note, the barrel (1.5” pipe) passes through all 3 fittings. The “ridge” in the 2”-1.5” reducer is dremeled out, but it’s still a nice tight fit.

Breech knife to cut potatoes:
Image

Barrel rest:
Image
Image
Image

The barrel rest is a short section of 2” pipe with “grooves” filed/sanded into it to make it fit snugly against the 4” chamber below it, and the ring of 2” pipe above it. This allows the 1.5” barrel to turn inside the 2” rings, and holds it securely in place. There are grooves cut in the 2” barrel-holder rings to keep the plastic zip ties from moving. Zip ties are strapped down tight with plyers. I’m building a second set of barrel holder rings for a 2” sch80 barrel (golf balls anyone?).
Note, there are two barrel rests total, though the pictures only show one. Both are made now, but I only had one done when I took the pics. The second one sits about 10” back from the first one, towards the U bend.

Over/under gun dry fit together:

Image
Breech open

Image
Breechclosed

Image
Valve end

One of my objectives was to minimize holes in the chamber, included those for wiring. Here’s how I’ll pass the wires for the spark strip and fan through the chamber. Where the back (valve-side) bell reducer is attached to the chamber, 4 of the bolts will have this setup:

Image

The stun gun circuit, safety, and fire switches will be contained in the rear handle. The battery and switch for the fan will be contained in the front handle.

The entire gun will be painted glossy black when everything is glued and secured.

Here are pics of my faithful old gun which will be donating it’s propane meter and rear handle to the new over/under gun.

This gun is years old. I built it back when I was 14 or 15. It’s seen 600-700 potatoes through it, and had the police called on me three times (The cops all thought it was awesome, too). It served me very well. It’s shown here with a short “noise-maker” barrel. I have barrels upto 10’ long for it that will be adapted for the breech-loading system on the new gun.

Image

Image

Image

Image

Note the unregulated propane setup. It works wonderfully.
Open the needle valve from the torch and the first (tank-side) ball valve, leaving the second (chamber-side ball valve) closed. Wait for the gauge to read 50psi, and close the first valve, then open the second valve to vent the “shot” into the chamber. Close the second valve and open the first, and repeat the process (two “shots” at 50psi seems to be the right mix). Turn off the ball valve and vent the propane from the meter pipe when you’re finished shooting.

Anyway, Please give me your opinions on this setup before I glue it. If you have any additions or suggestions to make, PLEASE GO FOR IT! I want this gun to be as nearly perfect as possible; I don’t intend on ever building another combustion spudgun.

Peace,
Pete Zaria.
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Last edited by Pete Zaria on Thu Jan 25, 2007 3:09 am, edited 2 times in total.
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Unread postAuthor: MrCrowley » Sat Jan 13, 2007 4:40 am

Woah :shock: , As soon as I read the thread title "Pete Zaria's..." I knew it had to be good. Don't worry you didnt disapoint me :P . Nice job on the barrel support and make sure to paint that ball valve :wink: Looks funny b/c its white :roll: I like the way it is, Don't see any reasons to change the design layout. Do you know how much it will weigh when finished propane and all? Oh and make sure to remove those barcode stickers :P .

Looking foward to see this finshed....
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Unread postAuthor: Pete Zaria » Sat Jan 13, 2007 4:47 am

@ McCrowley,
Yep, I'll be painting the whole thing glossy black end-to-end (except for the propane meter and system) when it's finished :)
I'm glad you approve.

__________________

It's good to be a forum patron. There's a lot of cool guys here. I've had a lot of help designing this gun, and I need to give a huge THANK YOU to the guys here at SpudFiles.

Again, PLEASE GIVE ME ANY IDEAS/SUGGESTIONS/COMMENTS YOU HAVE BEFORE I GLUE THIS BABY TOGETHER! I want to make it perfect because I'm probably never going to build another combustion gun after this.

Peace,
Pete Zaria.
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Unread postAuthor: mark.f » Sat Jan 13, 2007 8:26 am

I approve of everything, yet I have a suggestion.

Nothing major, it's just that that barrel rest looks a little flimsy... like mine! On a little BS gun I made, I used PVC for a barrel ring support, and I find that if you tighten hose clamps too tight over them, they will grab the barrel, and if you don't tighten them tight enough, they're floppy. There's no in between for me.

If your support feels a little floppy, I'd suggest taking a 2" SCH-80 steel pipe nipple about maybe 3" long, and then bracing that in a support instead of that PVC ring you have on your cannon. If it scratches your barrel and you don't like that, replace it with a 2" SCH-40 steel pipe nipple and line the inside with a soft material like cloth.

Thanks for listening!

Mark
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Unread postAuthor: Recruit » Sat Jan 13, 2007 9:28 am

I say great job.
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Unread postAuthor: Pete Zaria » Sat Jan 13, 2007 1:44 pm

markfh11q wrote:I approve of everything, yet I have a suggestion.
Nothing major, it's just that that barrel rest looks a little flimsy... like mine! On a little BS gun I made, I used PVC for a barrel ring support, and I find that if you tighten hose clamps too tight over them, they will grab the barrel, and if you don't tighten them tight enough, they're floppy. There's no in between for me.
If your support feels a little floppy, I'd suggest taking a 2" SCH-80 steel pipe nipple about maybe 3" long, and then bracing that in a support instead of that PVC ring you have on your cannon. If it scratches your barrel and you don't like that, replace it with a 2" SCH-40 steel pipe nipple and line the inside with a soft material like cloth.
Thanks for listening!
Mark


Mark,
I sanded the pieces of pipe so they fit snugly against the chamber and "barrel ring" and they seem to take a fair bit of abuse. I'm pretty sure they'll hold, but if not, I'll definitely consider the steel nipple idea. Thanks.

Recruit wrote:I say great job.


Thank you very much.


Anyone have anything to point out before I glue it? :D

Peace,
Pete Zaria.
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Unread postAuthor: SpudBlaster15 » Sat Jan 13, 2007 2:00 pm

Instead of attaching the 4" to 2" reducer with bolts (you may have leak issues), I would buy a 4" cleanout adapter and a 4" threaded adapter. Then you could use a short piece of 4" pipe to connect the 4" to 2" reducer to the threaded adapter, and have a leak proof, solvent welded system that can be detached by unscrewing the threaded joint.
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Unread postAuthor: Pete Zaria » Sat Jan 13, 2007 2:15 pm

SpudBlaster15 wrote:Instead of attaching the 4" to 2" reducer with bolts (you may have leak issues), I would buy a 4" cleanout adapter and a 4" threaded adapter. Then you could use a short piece of 4" pipe to connect the 4" to 2" reducer to the threaded adapter, and have a leak proof, solvent welded system that can be detached by unscrewing the threaded joint.


I thought long and hard about this exact idea. I decided against it because
A) 4" male and female adapters are expensive.
B) I don't want to trust the entire pressure of the combustion chamber to a set of 4" threaded fittings. It seems like it would be the weakest point on the chamber, therefore the most likely to fail.
C) I'd have to Teflon the threads and crank them down tight with a wrench if I wanted to get it "leak proof", so I figure whichever I used (threaded fittings or my current setup) it will leak a teeny bit. So what, it's a combustion, heh.
D) If I used threaded fittings, I'd still have the problem of passing the wires through the chamber. I'd have to drill small holes where a fitting and pipe overlap, pass the wires through, and epoxy the area around them. I think using the bolts to pass juice through to the chamber is the easiest solution.

Anyway, yeah. I thought about this a lot too. I appreciate your input, Spudblaster.

Once again, anyone have any suggestions/comments to make before I glue 'er?

Thanks so much to everyone that's helped me with this project. That means most of you at Spudfiles in one way or another.

Peace,
Pete Zaria.
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Unread postAuthor: SpudBlaster15 » Sat Jan 13, 2007 2:32 pm

I dont think a threaded connection would be likely to fail or leak, but I hear you about the cost. Around here, 4" ABS cleanout adapters and threaded adapters are $15 each! Make sure you use LOTS of bolts, ABS isnt the more dense material around, especially cellular core (is that what you are using?). It seems likely that the pressure on the back of the gun could eventually tear the bolts through the pipe if you used too few of them.

I think you would be fine to glue and paint it right now, I glued my ABS combustion gun together in -20*C. You just have to make sure the cement can is warm, I keep it in my pocket while setting everything up. Additional cure time is nessesary too.
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Unread postAuthor: Pete Zaria » Sat Jan 13, 2007 3:37 pm

SpudBlaster15 wrote:I dont think a threaded connection would be likely to fail or leak, but I hear you about the cost. Around here, 4" ABS cleanout adapters and threaded adapters are $15 each! Make sure you use LOTS of bolts, ABS isnt the more dense material around, especially cellular core (is that what you are using?). It seems likely that the pressure on the back of the gun could eventually tear the bolts through the pipe if you used too few of them.

I think you would be fine to glue and paint it right now, I glued my ABS combustion gun together in -20*C. You just have to make sure the cement can is warm, I keep it in my pocket while setting everything up. Additional cure time is nessesary too.


I was planning on using six big bolts with nuts and washers on both sides. Do you think 8 would be a better idea?

I'm very tempted to glue and paint it now, but I want to "do it right the first time". It's still below freezing outside. I might just heat up my garage with some shop heaters and do it in there. I'm excited to get it done :)

Thanks so much for your help everybody. Keep the ideas coming!

Peace,
Pete Zaria.
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Unread postAuthor: SpudBlaster15 » Sat Jan 13, 2007 3:53 pm

6 large bolts with nuts and washers should do the trick, but I would use 8, just for peace of mind.

BTW, the gun looks great, I cant wait to see the final product. It looks like you really put some thought into it, and I cant see a single flaw.
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Unread postAuthor: MrCrowley » Sat Jan 13, 2007 3:57 pm

Pete Zaria wrote:I was planning on using six big bolts with nuts and washers on both sides. Do you think 8 would be a better idea?


You can always start with 6 bolts and change to 8, its alot harder to go from 8 - 6 :P

Only thing I can think of to improve the gun is 2 barrel supporters for when you open the breech.....kind of like PVC Arsenal's Omega gun breech desgin here Image

Just to add support
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Unread postAuthor: Pete Zaria » Sat Jan 13, 2007 4:01 pm

SpudBlaster15 wrote:6 large bolts with nuts and washers should do the trick, but I would use 8, just for peace of mind.

BTW, the gun looks great, I cant wait to see the final product. It looks like you really put some thought into it, and I cant see a single flaw.


8 bolts it is, then.

Thanks for the compliments. I have put a lot of thought into it; I wanted to make one "ultimate" combustion gun. After this I intend to build a nice metal marble gun and then a hybrid, so this will likely be my last combustion. I wanted to do it right :p

I need to get the nuts and bolts, some more wire, and the stungun circuit and it'll be finished. I have a BBQ sparker that will jump all 4 gaps on the spark strip I made, so I could use the grill sparker until I get the stungun. I'll get the rest of the stuff from home depot tomorrow and glue it up ASAP. I'll post pics during the build process. When it's done, I'll post hang time test results and some destruction pics (I have an old computer or two I could shoot some concrete-filled caulk tubes at...)

I know I've already said it 5 times in this thread, but THANKS SO MUCH to the guys at spudfiles. This project would not have happened without you. Keep the ideas/suggestions coming!

Peace,
Pete Zaria.

Edit: It has two barrel supports now. I added a second one about 10" towards the U bend from the first one. I'll take pics when my GF gets back with my dig camera.
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Unread postAuthor: MrCrowley » Sat Jan 13, 2007 4:10 pm

Well I think all thats left now is to get Sean(Gort) in here with his expertise(sp?) and he can do his inspection of the gun.
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Unread postAuthor: Pete Zaria » Sat Jan 13, 2007 4:14 pm

Heh, it's the truth. I'll probably glue it tomorrow or Tuesday, so I hope Gort and/or some other combustion experts can critique it before then. Thanks a ton guys.

By the way, how long do you think the spark strip should be? The one I made is 8" and has 4 gaps. I plan to position it near the ball valve end of the chamber. Opinions?

Peace,
Pete Zaria.
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