modeling clay bulb molds

I’m new to r/c sailing but have poured several keel bulbs using modeling clay for a mold. I first carved the shape I needed from a block of hard modeling clay then I melted a lead sinker in an old can (the kind you get with beans, creme corn exc…) then poured it into the mold after it was hard it came right out. Has anyone ever done this before? If not this method works great.

this method is used very often but it is also dangerous.
If the clay is not perfectly dry the residual humidity, in contact with the 300°C celsius melt lead, may generated sufficient high pressure as to produce a big “splash”.
You need several precautions to protect yourself. I heard that persons went to hospital with serious burnings.

There are others methods much less dagerous observing some precaution since lead is very tossic. So the use of glowes is a must.

In the IACC120 Cup discussion, derived into AC33 construction, I explain,, the use of the RTV-139, high temperature silicone, the advantage is that the mould is ready in 24 hours and do not presents risk of splashes.
The second method consist in cutting and assembly several layers of pre-cut lead foils and than shaping them to the desired form/weight:
That’s all what I can tell on the subject !

I’ll add my experience to the thread. Plaster will make a great mold, but with the same problems Claudio points out, moisture. Even multiple, heat, cool, drying cycles will leave you with a mold only good for a few pours, before cracking. And a cracking mold with molten lead running out is a dangerous situation.

My current experiment is to make a two part mold using “Castable refractory mortar”. Do a search for suppliers. It is used in kiln making, and should not self destruct with multiple uses… I hope!

Note, concrete will NOT work over the long term, as portland cement will disintegrate with repeated heat/cool cycles.

I’ll let you know how it works when I get around to melting some lead!

Next time I’m going to try a two part mold similar to this but using hi-temp silicone.

It would use less silicone(covers my cheapness) and would somewhat isolate the lead from the plaster(covers my impatience and cowardice)

I have used the high temp silicone to make a 2 part mold, but it began to deteriorate after each pour. It definately has to be supported by plaster or similar to hold it’s shape.