Tuesday, 1 May 2012

Firing blanks?

The key with the edge made from solder worked so well but it was such a pain to actually make the blank. I decided to look at casting one. The idea was to make a mould of a normal key blank in a high temperature epoxy so that the filed down blank could then have the solder cast onto its edge. This did not work, firstly I tried to get clever with my mould making and that failed but secondly I think the approach was doomed to fail. OK, let's start with the mould making, I applied some foil tape to one side of the blank carefully burnishing it into the cuts on the side of the key. This foil would form the parting line the the mould. I coated the other side of the key in Vaseline (petrolium jelly) and dunked it into a little tube filled with epoxy. The tube was the backing from the foil tape, the epoxy was "JB weld", quite famous but it is my first time using it. 10min in the oven at around 70 and it was set. I pulled off the wax paper and sanded the sides of the block to reveal the foil tape and then split the mould with a screwdriver. It did split but the vaseline did not do a good job, possibly the heat was not such a good idea. Normally I use wax and will do in the future, that was fail part 1.

Fail part 2 involved my salvaging what I could of the mould and trying it out "by hook or crook". The result was failure. This is more than just casting, if you want the solder to really stick to the brass blank then the blank must be up to soldering temperature, this ensures the solder retains a low viscosity as it passes over the surface and wicks into the microscopic details of the brass. Otherwise it just freezes on contact or sits on the surface like a balloon full of water. But the fact that the resin is a fairly good insulator meant I could just not get the solder to flow into the mould and contact with the key, the resin also got rather soft (still awesome stuff though!). The mould also needs to be up to temp and I think the easiest way for that is if it is made from aluminium. This is possible but I am not sure if I want to go that far right now. If I did I would cut a blank in half, pop it on the flatbed scanner and create some CAD for a mould, then mill with a little ball ended cutter (I have down to 0.5mm). The mould can be a little oversize, as long as it cuts down the work, hmm maybe tomorrow.

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