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I made a small radius attachment for my 9" lathe some years ago, but wanted one for my big Storebro lathe. One of the very few advantages of breaking your shoulder is that you have lots of time to catch up on the project list, subject to your reduced capabilities. I think it took longer to decide exactly what I wanted to make than it took to make it. I was originally going to cut the frames out of aluminum plate, but it was only 5/8" thick. I finally decided to weld up steel frames.

Here's the outer frame ready for welding, complete with bevels for the welds. Not long before the accident, I upgraded my MIG to a Miller 211. I'd used it a bit, but never really rung it out. Since the outer frame is made of 3/4" thick steel, I cranked the welder up to max on the automatic settings and had at it. Man, that's a nice welder! It filled in the bevels very quickly.

I made the attachment to mount in the four-way tool post, so I wouldn't be changing the height setting on my biggest QCTP block. That way, it's on lathe centre every time.

Since I like using square HSS bits instead of round ones, I needed a 5/16" square hole through the inner frame. I've done this before, for a boring bar. Drill a hole, then force a HSS bit blank through the hole and tweak it with a file. This time, it was much easier with the 20-ton shop press. I filed the entry corners before, so the bit would start straight.

I drilled the inner frame with two pivot lines to make it easier to do smaller rounds. I made it to handle up to a 3" ball, just in case.

You can't make a knurler without at least one knurled part and you can't make a radius turner without at least one ball handle. This one is almost 1 3/8" in diameter, with a 1/2" shaft.

Here's the finished attachment. The handle also serves as the setscrew to hold the handle and hub onto the top of the vertical shaft. You can see the spot beside the bit where I had to grind out some material to allow the ball to be turned close to the shaft. I'll probably make a second inner piece - a straight shaft with a 1/4" bit for turning small concave radii, such as you would need for a new head for the pipe bender to handle odd pipe sizes.
Looks good! Another one of those things on my unofficial todo list.
(10-08-2016, 08:55 PM)Hawkeye Wrote: [ -> ]"The handle also serves as the setscrew to hold the handle and hub onto the top of the vertical shaft."

Nice job Thumbsup '

Why is the "vertical shaft" so long (tall)?

I suspect so that it keeps your knuckles out of the spinning chuck, plus, so it works with the larger 4-jaw chuck.
Very nice Mike Thumbsup  Smiley-signs107 
a job well dune
Al nailed it. my 4-jaw is 10 1/2" in diameter. Plus, the lathe has some very nice brass and glass drip oilers that I don't want to damage.
Oh, and I forgot to say, lovely work. Need to make one for myself. I want to incorporate a quick-change holder built into the radius turner.
Using your down time wisely I'd say, thanks for showing the build... and the education.

How do you adjust the ball diameter? If I'm looking at it correctly, your swing depends on which of the holes you have the center section sitting in. But that's only two sizes. Is that how it works?
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