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Radius turning tool project

John Conroy

Well-Known Member
Premium Member
I have been thinking about building a radius turning tool for a while now. I have been working on plans in my head for a couple of weeks now and got to work on it this weekend. My lathe has t-slots on the cross slide so I machined some t-nuts and a mounting plate for the body of the radius tool. The compound does need to be removed to use it but the cross slide stays more centered in it's travel so I chose not to mount it using the compound bolts. I copied a design I saw on another forum but added a second bearing. It has a tapered roller bearing on the top and a thrust ball bearing on the bottom. The bearings are packed with grease and slightly preloaded which makes for very smooth stable turning action. The cutter head is mounted to an adjustable slide that is secured from one side with four m8 set screws. The cutter head can be mounted 2 ways to provide more options for different size radii. It can machine a ball up to 3.125 inches in diameter and can be adjusted to make a large range of concave radii as well. I made a couple of balls, one for the handle of this tool and 1 for the spindle clamp on my mill. They came out pretty smooth and didn’t need much polishing to be made shiny smooth. It uses a TCMT insert which has a 6 degree positive rake.



Active Member
VERY NICE! I really like your ball bearing set up. I made a ball turning tool myself but didn't really know how to do the ball bearing thing. I ended up using a non tapered bearing but it's not quite right.

I was showing my wife my newly completed project and she asked what I needed a ball turner for and I told so I could make a ball for the handle of the ball turner!


Active Member
LOL..... I have encountered books that suggest projects that require the project itself to complete.
Oh ya I forgot to tell you the first half of my funny story...
So I was first working on making a milling attachment for my little lathe and my supportive wife asked what I needed that for and I told her so I could do some milling for a "radius turner" project... "oh I see" she says...


Ultra Member
Premium Member
I like it! Your design actually looks more solid than a Holdridge C-frame sitting up on the compound. You'll probably find many uses for this. A lot of machinery accessories are just nicer looking with ball ends or even simple round-overs & maybe a bit safer too. I like looking at older machines with their fengshui elliptical blended profiles that pleasingly fit the hand. Or you can be the first kid on your block with egg-shaped motorcycle bar end weights! LOL. Good project.


Active Member
You make a mounting block to fit your lathe and advance with the cross slide if mounted there or your compound (if big enough) and if mounted there