Internal Radius Help

Premier DT · Oct 28, 2020

So, I am new to CNC machining and have recently been getting my head around some basic OD turning, grooving, threading and even some Y-axis live tool hex flats. However, next I want to tackle some half circle radii. Both internal and external. Our machine has a sub-spindle if necessary but I'd much rather do everything on the main spindle if possible, especially boring.

The part in question has a 1mm radius, half circle, on the ID. My idea is to rough it flat as big as I can and then go in with a grooving tool of some kind to clear out the material between the 2 radii, however would I be able to cut a small radius with a grooving tool? Same question would go for radii on the OD as well. I'd rather not use a left hand tool if at all possible. Anyway I'm new to this, especially boring (broken 1 tool already) so any help is appreciated!

DouglasJRizzo · Oct 28, 2020

Premier DT said:
So, I am new to CNC machining and have recently been getting my head around some basic OD turning, grooving, threading and even some Y-axis live tool hex flats. However, next I want to tackle some half circle radii. Both internal and external. Our machine has a sub-spindle if necessary but I'd much rather do everything on the main spindle if possible, especially boring.

The part in question has a 1mm radius, half circle, on the ID. My idea is to rough it flat as big as I can and then go in with a grooving tool of some kind to clear out the material between the 2 radii, however would I be able to cut a small radius with a grooving tool? Same question would go for radii on the OD as well. I'd rather not use a left hand tool if at all possible. Anyway I'm new to this, especially boring (broken 1 tool already) so any help is appreciated!

I had a job like that when I worked for dad. I used a Kennametal/Manchester dogbone style groove tool and would rough out the grooves and leave (in my case) 1/8" in the bottom to generate the radii with G76 on on Okuma or "R" on Fanuc depending on which machine was open at the time. I actually drew out the coords on graph paper with my X/Z target points. Came out well.

JonFinn · Oct 28, 2020

Grooving tool should be fine for finishing the rads. finish the grooves so that you have two flat tops where the radii need to go. You can then either finish them in one shot or - depending on the the material - you could start at the top of each radii and finish the front side (+X/+Z) and then the back side (+X/-Z). Either way, you obviously need to account for the width of the groove tool when finishing the back side of the radius.

pcasanova · Oct 28, 2020

groove tool id or od I always give the leading edge d1 and following d2. program to print and adjust offset to get the widths/positions. they share the same x but z will differ by the grooving width. just have to watch when shifting offsets. some controls will just rapid the tool the the position, other (siemens what I run) takes the next feed into position.

Premier DT · Oct 29, 2020

JonFinn said:
Grooving tool should be fine for finishing the rads. finish the grooves so that you have two flat tops where the radii need to go. You can then either finish them in one shot or - depending on the the material - you could start at the top of each radii and finish the front side (+X/+Z) and then the back side (+X/-Z). Either way, you obviously need to account for the width of the groove tool when finishing the back side of the radius.

I've done a chamfer with a parting off tool, but I wasn't sure if a groove tool would be able to handle that sort of axial cut, but as long as there's clearance behind it (like I did for the parting chamfer) the tool should be ok? In that case that saves a lot of bother with swapping spindles for them.

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