I broke the lathe parting tool

I managed to break the parting tool on the lathe and not really sure why/how it happend. I was trying to part off AL that was about 1.25 in diameter. Lathe speed was I think 550 rpm and I was feeding by hand. I managed to get ~ .25" deep when it broke off the insert and bent the tool. I wasn’t trying to force it into the material, I was probably .020-.030" from the 3 jaw chuck. I think the part off too bent to the right, not the chuck

Anyways wanted to let everyone know. I’ll order a replacement tomorrow since I broke it.


550 is kind of slow but I suspect there was an angle to the tool as it entered.

Parting tool needs to be on or a little below center and rpms are way too fast

How much relief angle is there on the parting tool

If the parting tool isn’t making a nearly precise 90 degree approach toward the axis of rotation the work piece and parting tool can bind up abruptly, ending western civilization. What happens is the work piece material on one side of the tool binds it up behind the cutting edge. Typically, there can be some warning, chattering and vibration (lathe snarling). Was that the wide or narrow cut off tool? Many a time I have resorted to the hack saw for cut off (using the chuck as a vise and manually sawing, NEVER apply the hack saw to a part in rotation!)

Part off should be done close to the chuck, but 0.02 -0.03 inch is closer than necessary. You are a very excellent member if you replace the tool.

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Question for those who know more than me. I looked on Shars for a MGEHR1616-2 part off tool. There was about 3 pages of choices. I don’t know which one to purchase. Can anyone tell me which one to purchase or inserts used on the tool?

There was no chatter/vibration. I could feel it cutting well, then pop. I didn’t square up the tool against the chuck before using, but it was not visibly out of square

Always good to check square, but there is always the possibility that the tool was damaged before you used it.