How to turn an inside radius - GWR safety valve bonnet - on the Unimat?

WM183

Western Thunderer
Hi folks.

In a former life (in the 90s, ack) I was an automotive machinist, but I haven't turned metal in anger in a long while. I've made some simple stepped things, but I need to turn a new safety valve bonnet up for my 1366T build, as the white metal one in the kit is horrible. Oddly the chimney is ok, and I will likely use it.

The fact the safety valve bonnet is often shown as unpainted brass - and nothin looks as much like brass as brass - is a big part too =)

I've never turned an inside radius before, however. Is it just a matter of a radiused cutter? Or can I fettle and bodge it with a file? I have a good diagram of the part in one of the GWR Pictorial Guides but have no idea how to mechanically approach it? I have a solid Emco 3 claw and a good chuck for my tailstock, and an array of drills and cutters and all.

Help me make metal into smaller bits of metal!

Amanda
 

simond

Western Thunderer
I don't believe the 1366's originally had polished brass SV covers, but stand to be corrected, though it does appear that it's common in preservation

(and rule #1 applies of course)
 
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