Bit of a digression, but for smoke box doors on 2 of my locos I have approximated a curve with 3 low height conical sections. You have to look very closely to tell.
Similar to Ian P’s method, I made a large radius attachment. The only setting up requirement is that the pivoting radius arm is straight when the tool is on centre (unless the work is required to have a central flat, or point, or be toroidal).
<p style=”text-align: left;”>An excellent attachment Charles, I guess most of us could make something similar from photo but I would agree with Clive. It would make a good article for the magazine, certainly better than my template method.</p>
Andy.