cold cast alu stalk with bubbles?


terminal fettler

Active Hunter
hi everyone, im working on the bmx potty + filler helmet, in the photo below youll see my custom cold cast alu stalk(hollow). My question is , whats the best way to eliminate bubbles in the resin? Any pointers would save me making hundreds of these "swiss cheese stalks" before i finally get it right, all ideas greatfully received:) Cheers TF

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Prymer13

Well-Known Hunter
I thought I had read somewhere that bubbles in resin were caused by fast setting catalysts, or something like that, so a slower setting resin would allow the bubbles to rise and work them selves out of the piece.

Wish I could be of more help...
 

MARROW SUN

Active Hunter
I would redo the mold and make it to halves. That way when you put them together(at just the right time) your bubbles will be on the inside and not the surface.
 

terminal fettler

Active Hunter
thanks for the tips, i managed to suss out the problem. Too much filler in the resin causes air to become suspended because of the increased viscosity, by reducing the amount of filler or brushing into the mould, air seems to be eliminated.( the stalk with the wire is my third cast with no bubbles)(y) TF

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terminal fettler

Active Hunter
these are accurate in scale in that they are designed to fit my helmet, the dimensions are: full length 180mm/stalk width 9.5mm/thickness 7mm/top slot width 25mm/pivot bolt 10mm/crcle dia. 21mm. the hollow tube will possibly take six 1.5mm cables, these run down to a hollow pivot bolt which is held in place by a hollow allen nut inside the helmet...TF
 

terminal fettler

Active Hunter
BLUERAM said:
What did you end up doing to cast a hollow stalk?
its basically an aluminium tube which runs to a threaded hollow pivot bolt. this is placed into the mould and the open ends blanked to prevent ingress of resin (the mould has resseses to locate the tube end and bolt, this ensures perfect alignment) then you just pour in your resin! TF
 

terminal fettler

Active Hunter
I'm using GP polyester resin, the aluminium powder is added before the hardener, the amount is crucial and will effect the finish and consistancy. Good to experiment......TF
 
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