Machining question

I am about to machine the radius on the bottom of a loco dome for a garden railway loco, so fairly small radius - 1.5" to be be precise. Two ways I have thought about using 1. Mount stock material on a rotary table on a vertical mill with the table set back from an end mill to give the appropriate 1.5" radius. 2. Mount stock material on the cross slide of the lathe and fly cut the radius using a boring head in the lathe spindle.

My question is how can one cut/measure these radii with any degree of precision? I know that I can offer up a pre made template to check, which I am sure will be all that is required in this case, but if one did need to cut a radius to any degree of accuracy how would it be done?

TIA, Phil

When using a boring head you can set a bit of scrap opposite the saddle and measure between the two. I would actually fit the part to an angle plate on the mill and use the boring head on that.

The alternative is to zero the quill over an edge - side of vice, angle plate or block of scrap. Then move the tabhe by the radius, put your boring head into the quill and adjust the tool until it touches that edge it wil now be swinging a radius equal to how far you moved the table.

If using the rotary table & end mill method. Zero the table under the mills quill than move the table by the radius of the arc less half the cutter dia.

J

Edited By JasonB on 22/04/2014 11:20:48

Jason

Thanks a lot for your very detailed reply, why is it I can never see the wood for the trees? Should be able to try your method out in the next few days.

Phil