Positive - Negative Rake

[Kpar]

Well I've just finished a jig to cut internal / external keyways on my ALg30 Lathe using the compound slide. Seems to work ok but,
I'm having issues with grinding a suitable HSS tool bit. Positive rake seems to give a shuddering effect in steel while negative rake is ok with aluminum,
I cant seem to get a clean cut on steel or cast.
I did look at shaper tool bits and they seem to be all on a positive rake.
Any input would be much appreciated.

Kpar

 

[SmithDoor]

The positive rake works with all metals.
If cutting A36 a rake of 10 to 20° works great.
Some metals 30° will works best.
12L14 a rake of 5° to 7° works great.

Dave

Well I've just finished a jig to cut internal / external keyways on my ALg30 Lathe using the compound slide. Seems to work ok but,
I'm having issues with grinding a suitable HSS tool bit. Positive rake seems to give a shuddering effect in steel while negative rake is ok with aluminum,
I cant seem to get a clean cut on steel or cast.
I did look at shaper tool bits and they seem to be all on a positive rake.
Any input would be much appreciated.

Kpar