Cutting radius on lathe

[someidiot]

I'm sure there was a discussion of it on here recently, but I can't spot it at the moment.

Although I expect to do balls for the ends of cranks and such, I'm immediately interested in concave cuts on a shaft. Is this the kind of thing I need for it, or are there other styles (more or less preferable)?

https://www.amazon.ca/Assorts-Turning-Attachment-Base-Double-Similar/dp/B09H495HNM

 

[ChazzC]

You can make ball-ends or concave cuts using this method which does require any special tooling:

 

[someidiot]

Hmm. Okay, I get it. I hope you'll forgive me if I find it a little thinky- and tooly-intensive, as I'm starting out. The geometry is no problem, 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.

 

[whydontu]

For aluminum, grab a carbide roundover bit for a router. Hold it like a boring bar and feed in tangential to the workpiece. It'd probably work OK on mild steel, take it slow and lots of cutting fluid.

 

[Bandit]

You can use different size flat washers for some basic radius gauges.

 

[someidiot]

Although I expect to do balls for the ends of cranks and such, I'm immediately interested in concave cuts on a shaft.

So I think that means yes to the washer-gauges and no to the router bit.

 

[Bandit]

You can cut a flat washer in half and use the inside for gauges also.

 

[DavidR8]

I have used carbide roundover and cove router bits in the lathe to make radii and concave surfaces. Pretty high tool pressure so not great for tool steel or such but with patience it works.

 

[someidiot]

Initial forays will be with Delrin, so it's going to be pretty forgiving. Will probably move on to Al and SS later.

 

[fixerup]

I made similar tool like the one you posted a link. I found the plans on the web, it was good evening project to do in the shop. I was proud of my accomplishment and showed it to my machinist mentor and he said " cool tool, but I just do those type of cut freehand " Not sure if a concave profile could be easily done freehand.
I did the ball peen convex freehand for the hammer project in my high school course. But concave I don't think it would be possible unless there was a hole in the center.

 

[Golem Pens]

I've done concave with a cove router bit as well. Need to figure out convex myself.

 

[someidiot]

I've done concave with a cove router bit as well. Need to figure out convex myself.

Good - looks like I have a little learnin' to do about router bits too.

 

[Golem Pens]

Technically a core box bit I think