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1.25" piston hybrid-- SB15 inspired/clone- UPDATE 8/8

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: JDP12 » Sun Aug 08, 2010 8:30 am

I'll be postin an update later today on this gun, looks like it may get finished today but not tested til later this week thanks to JB Weld..

Also am starting to plan out a pump action type deal for this for long-term future project
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Unread postAuthor: JDP12 » Sun Aug 08, 2010 8:58 pm

not to double post, but just letting people know there's an update on the first post of the thread
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Unread postAuthor: SpudFarm » Mon Aug 09, 2010 12:17 am

The only problem I see is that the piston probably won't seal against the housing.
If you pressurize one side of the piston the rubber can probably just bend out of the way.

Use a pipe to the same diameter as your housing (SLIGHTLY bigger)to cut the rubber disk and use slightly bigger washers to stabilize the rubber materia.

Tell me if your deisgn works.
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Unread postAuthor: JDP12 » Mon Aug 09, 2010 8:44 am

Yea I'm not sure. I did buy some washers that are .1" over the diameter of the housing, I just don't want to have to grind those down unnecessarily.

On the current setup, there is only .1" of rubber exposed around the washers. I'm afraid if I go any less I'm going to run into issues with the rubber not being able to properly seal, so I'm hoping that this current configuration will still give me a proper seal against the housing.
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Unread postAuthor: SpudBlaster15 » Mon Aug 09, 2010 12:41 pm

The piston looks good, but I'd use a dremel with a sanding drum to smooth the edges of the rubber seals and ensure there are no gaps between it and the housing.

Spudfarm's concern regarding the rubber deflecting under pressure may be valid, but it really depends on the housing ID to washer OD ratio. How large is the gap between the steel components? On my setup, there is a .035" gap between the large piston washers and the inner wall of the housing.

Of course, if the rubber material is sufficiently thick, it can still form a seal between the outer edge of the washer and the inner surface of the pipe, even under full deflection.

Anyway, the launcher is starting to come together, and I can't wait to see the finished pictures. Hopefully everything works as you intend.
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Unread postAuthor: JDP12 » Wed Aug 11, 2010 12:51 pm

Yea I plan on smoothing it down a bit. The gap between the edge of the washers and the inside of the housing is .14", so possibly too much? the ID of the housing is 1.39". I have some washers that are 1.5", but I don't know if I want to grind em all down.
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Unread postAuthor: JDP12 » Wed Aug 11, 2010 5:16 pm

update page 1...
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Unread postAuthor: JDP12 » Sat Oct 09, 2010 3:35 pm

Don't want to triple post, but I'm home for the next three days, so progress has recommenced on this. I started gluin up the piston today, hopefully will get some more work done on it.
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