I'm making a Chunn twin and need some special slot cutters to make the space for the big-ends in the crankcase. Basically I need a 27mm dia semicircular groove 4.75mm long but with the proviso that the neck of the cutter will need to fit into an 8mm dia hole that will end up being the crankshaft bearing. This means the neck of the slot cutter will need to be around 7mm dia for about 15mm nearest the cutter head. Casting material is aluminium.
There seems to be essentially zero chance of buying such a cutter and as an alternative I see on Ishimura's excellent website at there is a description of some home-made slot cutters and I have some questions for the group about making some from silver steel :
Ishimura seems not to describe any relief on the back of the cutting edges, though the photos do seem to show a amall amount, can anyone tell me what the correct included angle of the cutting edge of each tooth should be for aluminium ?
Should I provide some side clearance by facing the sides of the cutter with the topslide over at say 5 degrees ?
Is it going to be possible to heat treat the finished cutter by holding it over a domestic gas hob or won't that get hot enough ?
All other comments received with interest.
Many thanks,
Mike