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Large Radius Turning

Posted: Sat Nov 11, 2017 12:12 pm
by Russ Hanscom
Here is another variation on a device for turning large radii - in this case 8", for a male and female die to contour 1/8" thick steel shims.

The die blanks are made out of scrap oak laminated together. The radius can be set at any length by changing the piece of allthread in the connecting link. The photo shows the concave profile being turned; to get convex, the link anchor is moved to the headstock side of the carriage.

In this application, a 1 7/8" dia pin centers the dies and the part to be formed.
And yes, it takes a while to clean up all the wood chips and lube the lathe.

Re: Large Radius Turning

Posted: Sat Nov 11, 2017 4:14 pm
by johnfreese
I have used radius rods for cutting radii. The radius rod is a piece of steel with a sharp point on each end. I center punched the tailstock and the back side of the cross slide. The rod is placed between the center punches and held there by pressure on the feed handwheel. The tool must be on the centerline of the spindle when the radius rod is parallel with the bed ways. I set the compound to feed parallel to the bed ways. Cut the radius by holding the radius rod tight using the feed handwheel while feeding with the cross slide. Use the compound to change the depth of cut. That makes a concave part.

Use the radius rod the same way between the cross slide and headstock to cut a convex radius.

Re: Large Radius Turning

Posted: Sun Nov 12, 2017 6:07 pm
by Russ Hanscom
You are correct that the link needs to be parallel to the ways when the cutter is in the center of the arc, and I used the compound to feed into the part.

I like the rod ends over a pointed rod in that the rod does not fall out if you forget to maintain it in compression, and in my case, the rod was at over a 45 degree angle at the extremes of the cut which would make it hard to keep it in a center punched hole, plus all of the parts were on hand.

Re: Large Radius Turning

Posted: Thu Nov 16, 2017 7:01 pm
by pete
Very clever and well thought out Russ. I've read a few times about center drilling the tailstock side of the carriage and doing the same at the correct matching elevation on the front of the tailstock much like John mentioned and using a pointed rod. But your method makes no permanent changes and as you say yours can do any reasonable radius that will fit in the lathe. The same could be done with the cross slide to put a male or female radius in the center of a shaft if there was enough room behind or in front of the lathe for the radius rod and a good anchor point.