Best way to turn a 1/2" radius in a corner

[737mechanic]

I am going to need to turn a 1/2 radius in a corner but after doing a 1/4" radius and getting some chatter I am left wondering if I am going to be successful in doing this. I am wondering what the most successful way to do this operation is. Below is the print showing the radius in question. My lathe is a 12x36 and it is new and tight. the first questions I have are:

1: What is the best way to grind a 1/2 radius HSS tool as far as relief angles and such to get the best possible performance.

2: What speed should I run to cut as much chatter out as possible.

Any tips will be much appreciated.

[Frank Ford]

To avoid chatter with a radius form tool, I find it useful to approach the corner radius slowly, taking shallow cuts, alternately feeding the tool in from x-axis and z-axis, so the tool cuts a little at a time on each edge before it's finished.

[RSG]

You don't spec the material in question! If I were to do that in aluminum I'd use a standard right hand HSS tool and cut a series of steps in a radius fashion within .010" then finish with the radius tool with a slower speed.

[johnfreese]

I use a tool with a smaller radius. I work the carriage and cross feeds together to sweep the tool around the radius. Only a small area of the tool touches the cut so chatter is not a problem. It gives a good approximation of the desired radius.

[mcostello]

I have seen Abom79 turn a radius into a corner pulling the chuck around by hand. Just put 99% of it in by power and then lightly scrape the chatter out. Never tried it, just watched the video.

[EOsteam]

A form tool was used to shape the flanges on the cast iron locomotive wheels and that worked best on the slowest speed on my lathe. 40 rpm and the tool was fed slow. Anything faster caused massive chatter.

HJ

[737mechanic]

Thanks guys for the input. Will let you know how it goes.

1018 HR is the material.

[Marty Feldman]

Have you looked at round insert tooling? eBay lists very many round carbide cutters. The holders can get expensive, and you will want a lathe that has both the guts & rpm, but it's one potential alternative to the grind-your-own approach.

-Marty-

[Richard_W]

I would use a Holdridge radius turner. Your lathe is too small to do it any other way. You can build one and many here have done that.