I need to mark some hole positions out on a cast-iron lathe backplate - is it OK to use a transfer punch and give it a good wallop? Or could it fracture? I've never worked with c.i. before but vaguely feel it might be "brittle".
Brendan
It's quite brittle compared to steel but you won't fracture a big lump of it with a centre punch. In fact you can straighten bent cast iron with a sharp whack. A guy I know who regrinds cast iron car engine camshafts checks them for straightness first on a dial gauge fixture and then gives the high spot a whack with a cold chisel. Surprisingly this persuades them it's in their best interest to lose the curvature. I wouldn't have thunk it myself until I saw it being done.
Yes but crankshafts are spheroidal graphite (SG) cast iron, also known as ductile cast iron (because it is ductile, which is why it is OK to use for things like drain covers). Your lathe back plate will almost certainly be grey cast iron, and pretty brittle. That said, a sensible use of centre punch should be OK. A light tap, not a good wallop.
What do crankshafts have to do with the price of fish? I'm talking about camshafts.
A light-tap it was ... thanks.
Brendan
Sorry, mis-read the post. Even so, grey cast iron doesn't sound the right material for a camshaft to me, except perhaps for a Lister.
I'll swap you one for a box of kippers
Regards, Tony
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