I needed a pair of identical gaskets for a 'Fluoslide' air valve (basically a flat spool valve) that I am re-building - the originals were somewhat battered but a bit complex with airways in the gasket connecting 'none opposite holes' on the faces as well as the various more normal holes and slots. Didn't fancy taping one out as the original was red fibre about 1mm thick and the faces are softish aluminium.
Hit on the idea of scanning one of the originals into a bitmap, and importing it into my pcb making program, touched up the damaged bits with the editor and exported the file to my Bridgeport Interact as G code. I had some 1mm card gasket material but couldn't devise a satisfactory way of holding it down - delaminated when pulled off double sided tape. Ended up using some 1.3mm black fibre material which is a bit harder than the original but stands up to peeling off. All worked out rather well !
I have tried all sorts of different ways of holding thin material down. Various double sided tapes (they are either too gummy or too weak or almost impossible to clean off). Special hot melt wax from J&L which I've found to be far too weak a bond. A vaccum table which is ok for things like signs that don't get milled all the way through, but fairly useless when items are to be detached from the main body of the sheet.
In todays gasket case I used 3M double sided tape and a 2mm slot drill at 15,000 rpm. The goo from the tape tended to clog the cutter but not to a disastrous extent.
AWEM