Turning Ball shapes

[Greg Williams]

Hi All,

 

I have to make a few parts that are essentially very accurate spheres, I have a twin spindle lathe and the workholding is all OK, so I can turn 2/3's of the part on the left spindle and the remaining area on the right spindle, Do you guys prefer Button style inserts, Round Grooving inserts or "V" style inserts for turning accurate spheres?

[Guest SAIPEM]

Hi All,

 

I have to make a few parts that are essentially very accurate spheres, I have a twin spindle lathe and the workholding is all OK, so I can turn 2/3's of the part on the left spindle and the remaining area on the right spindle, Do you guys prefer Button style inserts, Round Grooving inserts or "V" style inserts for turning accurate spheres?

 

Button inserts are better as cutting forces are distributed radially and hence less tool deflection.

It's easier to use button tools on harder to machine materials.

[Goldorak]

we do a LOT of inconel ball , and button insert are simply not rigid enough to hold tight tolerances

 

a 35 deg VNMG insert is the best way to cut accurate balls

 

an be absolutely sure that tour machine backlash is really well adjust, at the point where the X screw will rotate to the other way , if you got too much backlash, you will get a very nice toolmark (on Okuma this can be adjust in parameter )

[cappy]

we do a LOT of inconel ball , and button insert are simply not rigid enough to hold tight tolerances

 

a 35 deg VNMG insert is the best way to cut accurate balls

 

an be absolutely sure that tour machine backlash is really well adjust, at the point where the X screw will rotate to the other way , if you got too much backlash, you will get a very nice toolmark (on Okuma this can be adjust in parameter )

 

I cut a 1.500 dia. ball with an ISCAR .197 wide grooving insert. Works well. The ball is hardened to RC 55. We rough it out first leaving about .050" (.025" a side) harden and then finish it on a small LB15 Okuma.

 

Greg.

[Guest SAIPEM]

we do a LOT of inconel ball , and button insert are simply not rigid enough to hold tight tolerances

 

a 35 deg VNMG insert is the best way to cut accurate balls

 

an be absolutely sure that tour machine backlash is really well adjust, at the point where the X screw will rotate to the other way , if you got too much backlash, you will get a very nice toolmark (on Okuma this can be adjust in parameter )

 

Inserts aren't rigid or not rigid.

It's the complete tooling assembly that matters for rigidity.

The idea that button insert work holding isn't rigid is nonsense.

 

The key is the size of the tool nose radius.

Roughing with a larger button and finishing with a smaller button works great.

[Greg Williams]

Thanks for your thoughts guys. I have tried Buttons, grooving inserts and V styles. I think the best result comes from the Button inserts as they have the best "roundness" form. Grooving tools seem to be a bit hit and miss on the form and the tolerance.

[DavidB]

I'd like to see how your work holding for the sphere in OP2

[Guest CNC Apps Guy 1]

I like the button for roughing and the 35 Deg. for finishing...

[chall]

we use a SNMG for roughing and button tool for finishing