Round-nosed lathe tooling?

[mikey]

In the past, I've noticed that form tools do not like a lot of rake. The broad area of engagement allows a thin work piece to climb onto the tool, creating chatter. That led me to use anywhere from zero to 5 degrees of back rake and to make sure the tool was dead on center height; this worked better, for me anyway.

 

[MarkM]

If you want to do this with some sort of accuracy and make it manageable with little chatter is to use chords. There is a formula in the Machinery handbook. It has neen awhile but I had a job that required a large radius on a disk and this is how I went about it. Your basically making steps cutting equal depths on both side of the rad. Then work your way in to calculated depths and then leave .010 on final depth then blend in only to max depth.

 

[Nogoingback]

In the past, I've noticed that form tools do not like a lot of rake. The broad area of engagement allows a thin work piece to climb onto the tool, creating chatter. That led me to use anywhere from zero to 5 degrees of back rake and to make sure the tool was dead on center height; this worked better, for me anyway.

Thanks Mikey. Yeh, I figured there was too much rake since the the thin cutting edge was breaking down pretty quickly. When I
get a chance I'll regrind and try again. I was careful about making sure the tool was on center so I don't think that was a factor.

 

[Nogoingback]

If you want to do this with some sort of accuracy and make it manageable with little chatter is to use chords. There is a formula in the Machinery handbook. It has neen awhile but I had a job that required a large radius on a disk and this is how I went about it. Your basically making steps cutting equal depths on both side of the rad. Then work your way in to calculated depths and then leave .010 on final depth then blend in only to max depth.

Thanks Mark. I can look that up in Machinery handbook and give it a try.

 

[MarkM]

I made two form tools with rads. One as to size and the other had a slighly smaller rad. I free handed and blended the radius with the first tool then went to final size by plunging the proper radius tool to proper depth. Use a parting blade to make your steps.