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Trouble to parting off on a regular lathe


Sep 10, 2010
Oklahoma City, OK
I think what you're seeing is the heat staying in the chip, where it belongs, rather than transferring into the base material. And if going slow enough you probably got some weird stick/slip vibration stuff.

You know how an engine runs like shit if the idle is too low or comes apart when you send the speed to the moon? Well, your cutting tools behave similarly. That lathe has plenty of ass to push that 3mm parting tool, so learn about SFM, feed, and how apply them.

Tool alignment is also critical, normal to the work axis and on center, because these don't have much side relief.


Diamond; Mod Squad
Mar 27, 2005
Northwest Indiana, USA
CarbideBob already explained exactly what's happening at too low a speed. The chip is welding (attaching itself) to the carbide, then the chip is trying to do the cutting. After a short while or a little tool pressure because the tool isn't cutting well, the chip breaks away and takes some carbide with it. Now the cycle begins anew, except this time with a duller tool. After the chip rubs enough or the tool is considerably dulled you're going to hear some noise. Also the same or worse in some materials if you don't keep the cutting tool flooded. Good flood coolant is best for carbide in my experience, cutting oil second best. For best results you've got to keep it flowing, not just a dab here and there.


Mar 21, 2011
When you remove stock you have energy conversion, mechanical work to heat. With carbide inserts most of the heat goes into the stock. That is unfavourable, we want the bulk of the energy to go into the chips, 70 to 80 percent. In order to achieve this the just-being-removed stock must be heated up to almost burning, with hard turning you even see flames. Only enough surface speed will take you there, dictated by the hardness of the stock. The geometry of your parting carbide tool was calculated to a range of speeds you can look up with the documentation of the manufacturer. Do not think they simply make inserts for sale and use, there is a lot of study and experimenting behind them. Inform yourself about the recommended speed for the metal you work.

When I work as a hired turner I apply the wisdom that’s provided by the insert’s manufacturer. With HSS on mild steel your top speed will be around 40 m/min or 130 sf/min. At 2 mm diameter you’d have over 6300 revolutions per minute, which is too dangerous. Halt at that point, retract tool, saw work off by hand. If you wanted to part off completely at full speed, you’d need to hold the work by a second spindle, else it could fly through your head.
Apr 19, 2006
Manchester, England
When I was setting up for the group of women I mentioned earlier we used HSS tooling that I ground by hand. I also ground the cutting edge at a slight angle so it left a minimal pip on the item being parted off.

Regards Tyrone.


Dec 18, 2019
I never had much success parting then a friend recommended Iscar parting blades and inserts. Amazed at how tolerant they are to less than ideal speeds in everything from 316s/s to 7075 aluminium to 4140.

I'm a more of a home shop guy so for a 1" part I'd only run around 500-600rpm and .004" powder feed and use rigid dark cutting fluid applied with an oil gun. I think the correct tool and the correct feed to ensure cutting and not rubbing has more influence than RPM. Flood coolant would make the job even easier!!

Using a 13x24" Colchester with a 3mm insert so ,if everything is tight, your big lathe it should $#!+ it in!!