# Radius Turning Attachment



## GWRdriver (Apr 22, 2011)

I had gotten to the point where on my current locomotive project, and for projects down the road, I would need a good radius turning attachment (RTA) so a few weeks ago I stopped everything and built one. I based my project on an RTA design I was directed to on the Interweb and modified that to suit my lathe, the capacity I anticipated needing, and the materials I had on hand (some odd-ball chunks of cast iron.)

The base is a slice of cast iron which is made an exact copy of the base of my lathe compound and bolts on in the same manner. The compound sits on a 5/8" diam bored pivot pin hole so the RTA base uses what would have been a pivot pin as the boss which contains the pivot pin of the RTA dovetail base. The dovetail base is also cast iron and is slit to allow the dovetail slide to be snugged up or clamped solid. The tool post is also cast iron and will accomodate up to 3/8" tool bits. The largest OD it is designed to cut is 4" although if pressed it will go larger, and it will cut concave to about the same radius. The job took about two weeks of spare time, including research and drawings. There is a learning curve and minor bugs are being worked out, and an adjustable feedscrew is yet to be added.  It's shown here cutting the underside flare of a copper smokestack cap for a 1.5" scale locomotive.


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## Starlight Tools (Apr 23, 2011)

Harry 

Nicely made, will serve you well for years to come.

Walter


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## GWRdriver (May 1, 2011)

Thanks Walter. Here is the result of the last job on it, the stack cap for my current locomotive project. The diameter across the "fin" is 2.75"  I managed to get a really good finish on my final passes so the finish you see was achieved by giving that a touch with 600 and then 1200gr emery successively, and it has since been polished out with red rouge on a cotton wheel. Now all it needs is about 80 years of regular Brassoing and it will look like something.


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