Been working with metals for my job since fall of 03
Why are keycap molds so expensive? I mean, dont you just get a large chunk of whatever metal they use, CNC a hole and profit? Why do they cost 5k dolaroos?
Tolerances in the machining is the majority of it with setup costs from a shop capable of those tolerances. For example, paraphrasing from Sherline. To increase the accuracy of their benchtop milling machine by 3%, it would increase the cost of the machine by 10 fold. To put some numbers on tolerances for machining, surface grinding parts flat and parallel to within +/-.0003" is a very routine job that can be accomplished relatively with the proper machines. To get that tolerance down to say +/-.00005", which gives you a total allowance from largest to smallest dimension possible of .0001", takes about 4 times longer.
For example with my trade, I routinely have to do shaft alignments between an electric motor and a pump/gearbox/any other shaft driven machine. Typically we use the Optalign laser alignment tool, our union hall has a similar machine by Rotalign with all the bells and whistles that cost them $18,000. I normally am given tolerances for angular misalignment and offset misalignment both in the vertical and horizontal axis of .002". Depending on the setup, condition of the alignment when I get to it, condition of the base, this can take anywhere from an hour to 4 hours.
I have worked on some specialized equipment that had special couplings between the motor and gear box that required less than .0005" tolerance. When I arrived at that task, everything was already there, bolted up, and alignment was within .010" all the way around. That alignment took me 2 days with a good partner.
One other thing, with Bob mentioning that tooling changes take 2 hours, we are probably actually paying for 2 dozen molds or so. And there are going to be multiple cavities in each mold.
