[How do I?] Get A Straight/square Part Off On Lathe

RegisG

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I can not seem to get a straight, squared cut/part off on lathe. My blade is 1/16" x 1/2"x 4" M2 HSS. Every time I part something the face is tapered somewhat. Ends up like a shallow cone toward the center. Not pronounced enough to post a useful photo.
Is my parting tool too thin to cut off 1" diameter aluminum rod? I square it up with the face of the part so I'm pretty sure that is not the problem.

Appreciate any tips.
Regis
 
Make sure the blade is square, and the end is ground square. Angling the tip can remove the nub but can also cause the cut to skew. The cross slide on your lathe might also not be entirely square, or has worn over the years.

Or just part ~0.020" over length and face, that's what I always do.
 
Hi Regis,

Have you read some of the previous threads:
http://www.hobby-machinist.com/threads/parting-tool-question.46163/
http://www.hobby-machinist.com/threads/help-parting-on-a-curve.36268/#post-390537
http://www.hobby-machinist.com/threads/parting-for-idiots.32938/

(no insult implied with that last link....it's just the thread title!)

I know some of this has been covered before.

-brino
Thanks for the help. I thought I thoroughly searched but, apparently didn't.

I appreciated the links.
Regis
 
I haven't had too much trouble with smaller diameters, but sometimes issues come up with wider pieces. If they do, I just swap out the parting tool on the QCTP and face off the piece.
 
If it is a large diameter and you can, slide the parting tool back until only a little sticks out, then plunge to that depth. The tool will be more rigid and hence the cut straighter. Then you can slide the tool out a bit and do it again. Repeat as necessary to get to the middle.

I realize that those with lantern posts and hand ground HSS tools may have a problem with this, but if you have a factory tool, a T shaped parting blade or inserted blade for example, this can be a huge help. As a general rule, never hang out more than you need on the blade in any case.
 
This may seem elementary, but I assume you are using the cross slide, not the compound slide?


Sent from my iPad using Tapatalk
 
I grind my cutoff blade at a bit of an angle and do perfect cutoffs. My blade is 1/8" x 3/4",the "T" style cutoff,not those tapered cutoff blades used in the old Armstrong type holders. Those are not as good.
 
Cut it off in the band saw and face to length
 
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