MMM so it appears they were Famous last words.Originally Posted by FrankenWashie
Okay so we started our experiment proper with the Acrylic casting resin. This is what i am playing with,
the instructions are easy enough to follow, but be warned its a sticky gloopy STINKY experiment. Wear a respirator, don't do it in your workshop even if its got good ventilation like mine. Get out in the carport or on the patio.
I have set up a little mould to replicate the Hole in the FrankenWashie and mixed and poured to the halfway point-ish.
The bottom of the void has plastic sheet across it (HDPE) and this is sealed against the mould with masking tape.
I've left a little room for the resin to get under this to make an allowance for sanding. If this works the way I want it to then I will pull the same trick on the FrankenWashie body and be one step closer to finishing this off. (Famous Last Words I know.)
x
After giving the Resin a week or so to sure, I have found that there are a couple of issues.
#1. Part of the curing process is an exothermic reaction, as the resin sets up it heats, and the resultant heat caused distortion in my moulding blank. To be fair to the resin, the blanking sheet was just a fairly thin piece of takeaway container. This in turn led to an uneven surface as illustrated below:
The more eagle eyed among you will also spot that the resin has also retreated slightly from the left hand edge of the mould leaving a low spot. As you can see from the test sanding, there is a significant well in the centre form the distortion and the shrinkage.
#2. Also a normal occurrence from the resin is shrinkage on cooling. As the Resin sets up its normal exothermic reaction causes some minor expansion the flip of this being as it cools and finally cures, it experiences a bit of shrinkage (and we've all been there before, its not the end of the world and things expand again with a raise in temperature), not so for the resin. The shrinkage in my test blocks was accommodated by the open top of the respective moulds, the pour in those was somewhat more generous in depth than in my wooden mould so I ended up with this:
Once again those with eagle eyes will observe the nice dark line of adhesion stops right at the upper end of the photo and you have a clear section of resin cracked away from the edge.
So, what to do? I can get around the surface shrinkage, buy simply building a dam around the edge of the pour hole and pouring a bit deeper. This would mean a lot more work to scrape and sand back, and it wouldn't necessarily fix the shrinkage at the edges issue.
Given that there was a lots of rough surface for the resin to bind to in my little ply mould, the resin actually cracked through itself, rather than simply pull away from the mould. Given that both the Matai and the Merbau that border the pour area are quite smooth and close pored, this may cause the resin to simply let go.
A bit stuck at the moment, so if anyone has any clever ideas or alternative fill methods I'd welcome the input.
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