Build Log: MFIC

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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Blitz
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Sat Aug 03, 2013 4:22 pm

After thinking about the chamber plug, I felt it'd be better to stick with machining one from the UHMW I bought and nix the epoxy casting idea. The piece cost me $15 and my friend's going to show me how to use a rotary table with his mill and lathe what I want tomorrow. Not bad for $15 and some beer. :D

Before picture:

Image

(I cleaned it up since then. I bought the other two pieces for other things, figured what the hell.)
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wyz2285
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Sat Aug 03, 2013 5:45 pm

Good stuff, I wish blocks were sold here so I don't have to always mill one from a cylinder...
CpTn_lAw wrote: :D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Blitz
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Sat Aug 03, 2013 6:02 pm

Not even on eBay or something? :(
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wyz2285
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Sat Aug 03, 2013 6:07 pm

Blitz wrote:Not even on eBay or something? :(
The shipping gets up to 10x the price of the material :lol: and most of the time they don't ship to where I live.
CpTn_lAw wrote: :D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Sat Aug 03, 2013 6:13 pm

I meant, from sellers in the UK as well. :)
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Sat Aug 03, 2013 6:23 pm

Blitz wrote:I meant, from sellers in the UK as well. :)
Still so the shipping just doesn't worth it, because these materials are cheap but heavy.
CpTn_lAw wrote: :D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Blitz
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Sat Aug 03, 2013 6:28 pm

Oh, that sucks. Here, if I were to have something like that shipped, the post office has flat rates if it can fit in the box. Sometimes, it can be quite inexpensive.
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Sat Aug 03, 2013 7:26 pm

Massive project you've got going along there! Good attention to detail on the valve plug... certain members including myself would go for a wrap of teflon tape or two and some screws to hold a cap in place. :p

Also, isn't the "expression" (abbreviated for civility) HNIC, or is that what I get for listening to too much of the hippity and the hoppity and whatnot?
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Blitz
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Sat Aug 03, 2013 7:28 pm

I'm near a rather large metropolis area, but I'm not THAT urban. :D
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Blitz
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Sun Aug 04, 2013 8:16 pm

Gettin' there. Did some turnin'!

Image

Also, I figured I'd show what my chamber fan will probably be. Although I could spend a few more bucks and get a larger diameter. But, 80CFM isn't bad for an 80mm fan :)


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Sun Aug 04, 2013 8:57 pm

Hard to tell how big that plastic actually is by the picture :D

I'm very exited to see this finished :)
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Blitz
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Sun Aug 04, 2013 8:58 pm

When I took that picture, 7.5" in diameter.
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Blitz
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Mon Aug 05, 2013 3:06 pm

Having a hard time finishing up my plug (it's mostly done) -- but it's because I haven't had a chance to get to my friend's shop. Either tonight or tomorrow, I promise. :)

So besides finishing this plug, my next step is creating some support plates. These will serve two functions -- to hold the chamber and barrel together to alleviate stress from the tee and elbow fittings, and to facilitate the structure for the recoil sleigh. I wanted to get vibration-dampening U-bolt clamps for the barrel, as this will also grip it, but those type of U-bolt clamps run like $30 each, and I want four of them! I'm currently exploring a few options for the rails that the recoil sleigh would ride on. Once I'm satisfied with something that's cost effective (as in, not using CNC linear rails/bearings... This was something I briefly considered! lol), then I'll construct the support plates.

In general for most artillery in the 20th century, the recoil sliding use a U-channel that slide on a beam. That U-channel is sometimes part of the recoil sleigh that is part of the gun assembly, and sometimes it's on the carriage. I will likely put that part on the recoil sleigh, as that wouldn't need to be as long of a length. I'm likely going to use Impact-Resistant UHMW U-Channel 1" Base x 3/4" Legs, 1/4" Thick. At $2.64/ft from McMaster-Carr, that's fairly economical. I can just attach it with some countersunk flathead screws or something. Maybe I'll go pick that up today.

Rear view showing the rails on the cradle (carriage) on an M101 Howitzer. My rails would be a bit higher to allow unrestricted movement of the chamber, but similar concept.

Image

Thoughts?
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Mon Aug 05, 2013 3:32 pm

You can use a "ball bearing"ed slide rail (for large doors per example)
That's what I did. Offers a smooth sliding yet rigid mounting, also saves a lot of work.
CpTn_lAw wrote: :D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Blitz
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Mon Aug 05, 2013 3:44 pm

That was a thought. But those kind of slide rails just aren't economical on this scale, and my cannon is too heavy for anything short of industrial-grade, expensive units. I even looked at rackmount server rails, but they're too small for my needs. :(
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