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GSRocket
9th Oct 2010, 07:45 PM
Hi, I'm turning up a pattern from jelutong. The pattern will be used to cast a
part in polyurethane. The pattern is a bit bigger than a coffee mug.
I want a very smooth wax like finish. The finish will of course be duplicated in the cast items.
I'm equipping the lathe with a reversing switch especially for finishing.
My original idea was to coat the item with a thinned out epoxy resin,
sand to the finest finish and then coat with shellac and finish with steel wool.

But after scanning through these pages, there're probably better ways of doing it.
It seems Micro Mesh is better then sandpaper and EEE might be the product of choice to conclude with.
I would be happy to hear how you would go about finishing it.

underfoot
10th Oct 2010, 06:46 AM
I would be happy to hear how you would go about finishing it.
way back, when I was a patternmaker, I would sand jelutong down to about 240 grit
then give it a coat of Feast Watson "proof seal" (not sanding sealer) then sand with a 3m "microfine" foam backed pad. (spray putty also works fine if the tolerances are'nt too tight)
depending on what the item was being molded in I would use a dedicated synthetic mold release wax (resin resistant)

swallow
20th Oct 2010, 11:36 AM
Rocket Not know what the configuration of the pattern is it's a bit hard to give advice But why not just use a good quality paste wax, one with a lot of carnuba wax in it, then polish to a high shine. Then make a mold out of high strength gypsum cement thin the wax with alcohol paint the inside of your mold with the wax three coats, allow to dry ,buff to a hard shine and you should be good to go. At least for the prototype. for a permanent mold I would go to Silicone then no release is necessary and silicone is all but indestructible. Plus it allows for severe undercuts.

joe greiner
20th Oct 2010, 11:06 PM
I'd sand to about 400 max, polish with EEE, then apply paste wax and buff.

+1 for silicone. Encase the mold in a two-part plaster of Paris shell for rigidity. For high temperatures, use silicone sold for fireplace vents; more expensive, but more heat-resistant, even to molten lead. BTDT.

Cheers,
Joe