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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: jackssmirkingrevenge » Mon Aug 01, 2011 4:32 am

SpudBlaster15 wrote:It's generally not a good idea to use petroleum oils/greases on rubber parts, as it can cause them to swell. The 'Molybdenum' grease suggest by JSR is most likely to be a petroleum based grease with a small percentage of molybdenum disulfide added as an extreme pressure lubricant, so I would advise against it.


I've never had issues with this stuff and rubber seals, also I use it to lubricate my spring piston airguns.
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Unread postAuthor: saefroch » Mon Aug 01, 2011 9:34 am

I'm not using rubber, but silicone...
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Unread postAuthor: saefroch » Mon Aug 01, 2011 2:59 pm

Coming up on 24 hours, and the epoxy for the spark plug is still a bit sticky... any ideas? I tried to make sure I mixed it well...
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Unread postAuthor: Gun Freak » Mon Aug 01, 2011 2:59 pm

How hot is it where you live?
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Unread postAuthor: saefroch » Mon Aug 01, 2011 3:05 pm

It's rather toasty. I put it out in the sun for a few hours, got well over 100F.
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Unread postAuthor: Gun Freak » Mon Aug 01, 2011 3:07 pm

You didn't mix well :tongue3:
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Unread postAuthor: saefroch » Mon Aug 01, 2011 3:46 pm

I mixed that batch for 20 seconds, and there's no way I'm getting the spark plug out. Guess I've just gotta wait for my 1,000psi gauge to come and pressure-test it. If it holds, I don't give a f*ck.
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Unread postAuthor: saefroch » Mon Aug 01, 2011 4:40 pm

Leak tested. The spark plug epoxy sprung a massive leak at about 400psi. I cannot locate the hole, but I'll just sand off the area around it on the outside and re-apply. Expect more results tomorrow, I need to purchase more epoxy.
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Unread postAuthor: Gun Freak » Mon Aug 01, 2011 5:31 pm

:D
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Unread postAuthor: saefroch » Mon Aug 01, 2011 8:20 pm

Moar epoxy gotten, curing.
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 02, 2011 5:11 am

You seem to be having quite a bit of issues with epoxy, some troubleshooting:

How are you mixing it? These days I clamp a flat piece of something (thin metal sheet, plywood etc.) in my drill and use that to make sure it's properly mixed. Putting the components in a baine marie *before* mixing is also a good idea to thin them out and make them mix better.

Is there high humidity in your area?

Silly and basic questions, how are you calculating the proportions of resin and hardener? Are you mixing by volume or by weight? What do the instructions specifiy?
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Unread postAuthor: saefroch » Tue Aug 02, 2011 8:48 am

I'm only mixing small batches, so I've been using the corner of a plastic bag as a temporary container, and a bamboo skewer to mix (batches are usually <2mL), I am heating the components before mixing, and mixing for 20s.

Humidity has been rather high, yes.

I mix by volume, the epoxy that I buy comes in a sort of double syringe, push on the middle and it comes out both nozzles at the same rate.
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 02, 2011 11:22 am

saefroch wrote:I'm only mixing small batches, so I've been using the corner of a plastic bag as a temporary container, and a bamboo skewer to mix (batches are usually <2mL), I am heating the components before mixing, and mixing for 20s.


I would suggest using a small solid cup to ensure a more homogenous mix.

Humidity has been rather high, yes.


That doesn't help but not much you can do about it.

I mix by volume, the epoxy that I buy comes in a sort of double syringe, push on the middle and it comes out both nozzles at the same rate.


Make sure the nozzles don't clog up in an irregular fashion lest it interferes with the mix.
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Unread postAuthor: saefroch » Tue Aug 02, 2011 11:40 am

I'll try to find some disposable cups, but I'm starting to think it may have been related to the specific epoxy I was using. I switched to a different kind, and no issues at all yet. First two attempts cured completely in ~2 hours, no evidence of poor mixing, and I've just been mixing this stuff on a flat surface with a skewer.

Btw, putting the part out in the sun during summer gets it screaming hot, at least 200F. Much better than using costly electricity to speed up the curing. :P
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Last edited by saefroch on Tue Aug 02, 2011 12:26 pm, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 02, 2011 11:56 am

saefroch wrote:I'll try to find some disposable cups


I use deodorant caps, perfect :)

Btw, putting the part out in the sun during summer gets it screaming hot, at least 200F. Much better than using costly electricity to speed up the curing. :p


Too much heat might be a bad thing, remember material expansion. Also, personal anecdote, once I left a box mould held together with Araldite and filled with marine epoxy, the Araldite softened with the heat and fell apart, leaving me with a solid glob of useless parts when I returned...
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