Parting For Idiots

kyler

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Dec 12, 2011
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This topic has got to be one of the most discussed yet I'm still having problems. I apologize for bringing it up again.

The symptom is a concave surface on the cut-off piece. I mainly turn aluminum and haven't parted steel yet.

I shorten the tool to the minimum necessary.

I put the tool against the chuck and check for perpendicularity. I've even tried using a dial indicator to set the tool holder perpendicular.

ANy ideas?
 
How is the front of the parting tool ground? Is it ground parallel to the axis of the part, or is it tapered so that the part cut off will not have a "nub"

David
 
I am curious how this happens. Insure it is ground right as mentioned. It seems like if you had the cutoff blade turned a bit at an angle the contact with the side maybe causes this as it gets pinched and driven over gradually? I learned parting by asking questions so you will get it figured out here. there are also some videos out there on you tube on parting. I simply adjust the tool as short as needed as you did. I adjust it flat to the the faced off end of the piece and centered on the side of the work. I have also used the face of the chuck to adjust the cutoff tool flat as well and that worked too. There are several ways to get the cutoff tool adjusted to the center of the piece. Ski
 
Hi kyler,

After the parting is done, continue to run the tool all the way across the face of the work piece with the cross slide. If it continues to take off metal, the blade isn't perpendicular to the work. If it doesn't continue to take off material, but the face is concave, something is flexing under the load of parting, the blade, tool post, work piece, or whatever. Do you lock your carriage down when you part?

Tom
 
Once you reach center, if you try to cut the "far side", don't forget to reverse the spindle.
 
If you have a concave face after parting, could be your carriage is moving under pressure or your parting blade is flexing during the cut. Are you able to lock the carriage? Although I don't have the issue, it would,t matter to me cause I compensate & generally reface the part after parting anyway.
 
Do you get a perfectly flat surface when facing the end of a bar? If not could be the cross slide is not travelling 100% perpendicular to the lathe axis.
 
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