I am trying to make a device for soldering surface mount electronics boards. Basically it consists of an electric hotplate, a piece of aluminium plate, and a pyrex lid to cover the thing. To use it you assemble the PCB with all the components and solder paste, heat up the hotplate with the aluminium plate on top of it, put the PCB onto it, cover it with the lid, and wait until the solder melts. To make it convenient and safe, I need some kind of insulating board, maybe 12mm thick, that will withstand temperatures up to 300 or 400 C. Ideally this board will be easily worked with woodworking tools (saws, plane, router, drill or whatever) and will not be too crumbly. It should be highly insulating (i.e. with a 12mm layer the outer surface should be not uncomfortable to touch when the inner surface is at 350C). I have found various types of material which might do, but all of them seem excessively expensive, or unsuitable in other ways. I am imagining something made from vermiculite, or glass or rock wool, or some kind of heat resistant foam. I only need a couple of small pieces (say 30 x 30cm). I rather hoped that I might find someone with some offcuts.
Does anyone know of a material that would do this job?
Thanks - Rowan