Polyester resin seems to be shrinking.

Discussion in 'General Modeling' started by pandabarnes, Jul 25, 2015.

  1. pandabarnes

    pandabarnes Active Member

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    This is a continuation on my thread asking for casting advice which RogueTrooper kindly helped me out with. These parts are being cast for an e-11 blaster build.

    I cast my parts, and suddenly found that when fitting the front nozzle into the barrel, the cast part is slighty smaller than the original, enough that it now rattles around in the barrel instead of fitting snugly.

    I checked them against eachother, and sure enough it looks like the polyester resin i used has somehow shrunk during the curing process.

    I did put a tiny bit of black pigment in there too, because I thought it would help to have a nice dark base colour, but I'll try it without and see what happens.

    Anyone else had experience of this?

    Thanks.
     
  2. xeno

    xeno Well-Known Member

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    Polyester always shrinks a bit, and probably your mold too !
    Epoxy has a lower shrinkage but is more viscous, and some polyurethane resins even lower, you might give that a try (also less smell :)
     
  3. IEDBOUNTYHUNTER

    IEDBOUNTYHUNTER Sr Member

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    Exactly. Polyseter resin is junk. Always use Epoxy.

    As with any resin. The more liquid you use. The more shrinkage. You should always try to lay up the parts as dry as possible. They will be stronger and less shrinkage.
     
  4. pandabarnes

    pandabarnes Active Member

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    Cool, thank you both for the pointers, I'll order some epoxy resin and give that a go.
     
  5. RogueTrooper

    RogueTrooper Well-Known Member

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    Watch your brands also. I've found different brands of polyurethane give different results. Buy small amounts until you're happy with that brands results.

    Good luck!;)
     
    pandabarnes likes this.
  6. pandabarnes

    pandabarnes Active Member

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    I went with smooth-cast 310, happy with the results except the front nozzle which is still a little too small.

    I wanted to post back re epoxy because everyone I've tried to source some from has said I can't use it because it's too exothermic?!

    Not sure if that's the correct use of the word, but basically everyone keeps telling me it gets too hot for me to use at home this way.

    I can prob get away with the front nozzle, but I was curious about epoxy - any thoughts?

    Thanks.
     
  7. IEDBOUNTYHUNTER

    IEDBOUNTYHUNTER Sr Member

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    Really. i wouldnt do it in the house. but i do mine in the back yard or the garage. its totally ridiculous. yes it does get hot. and can smoke if you mix up a bunch, but if your just doing a layup with fiberglass cloth or matt theres no way its going to get so hot as to start a fire. Ive been doing fiberglass work for over 20 years. as with any chemicals you of course have to be careful. ive mixed a large batch on purpose just to get it to smoke. it goes crazy for about 40 seconds then dies off. not saying to do that. if you need help with this process PM me and i can help you out. because its used everyday no need to be afraid just need to know how to do it correctly.
     
  8. pandabarnes

    pandabarnes Active Member

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    ThanksIEDBOUNTYHUNTER - so is the glass fibre resin what I need? I actually have some of that already.

    I'm only casting tiny parts, the front nozzle on an e-11, so less than 5cm in all directions.

    Thanks.
     
  9. IEDBOUNTYHUNTER

    IEDBOUNTYHUNTER Sr Member

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    PM me and send me a pic that way i can see exactly what you will need
     
  10. pandabarnes

    pandabarnes Active Member

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    Thanks, just PM'd you some details.
     

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