Cutting radius on lathe

[whydontu]

I’m also guilty of misunderstanding your requirements. I was thinking of convex cutting, like ball handles. Yes, the Amazon cutter will work but it’s fiddly and chatters.

Ten minutes with a chunk of HSS and a grinder. Set your lathe feed to a suitable coarse thread, take shallow cuts because form cutters have to absorb a lot of energy to perform a cut.

 

[ChazzC]

. . . but I don't have a DRO or a dial gauge yet, nor the files I'd need for concave cuts. So while this is really good as a "no special tools required" approach, it still requires tools I don't have (though I know I need to get), making a cheap radius cutter seem more attractive.

If you don't have the tools to follow the procedure that is outined, you most likely will not have the necessary tooling/tools to "make" a radius cutter. Also, a dial indicator or DRO is helpful when using a radius cutter as well.

I also misunderstood. Seems like a radiused form tool might be good then.

A radius form tool for making concave surfaces would general a lot of tool pressure, even on Delrin/Acetal.

 

[Chipper5783]

It depends on how deep, relative to the radius - some of the ball turning attachments. For example the Stefan Gotteswinter setup based on a boring head (held in the tool post with a lift arrangement). Also the Hemingway kit (couple pictures of what I built), the tool can be displaced either side of the centre pivot - it would be hard to sweep the tool through 180 for a small groove.

 

[PeterT]

Not the best pictures but here is a simple intenal radii turner I made using 1/4" HSS cutter held it a pivoting block. Pretty simple but the radius of your groove dictates the geometry of the pivot block. If the radius is realtively small, you likely need a different gadget that facilitates that particular pivot center to cutter tip distance. there are lots of ways to accomplish this, just a matter of tool making vs tool purchase. Not all ball turning mechanisms can make internal profiles or may have dimensioal limitations.

Now depending on how many grooves you have make & how precisie it has to be, there is also the straight-in grooving tool method where you make a series of stepwise incrementing steps, precalculated DOC & smooth the steps with a file.