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First check leveling or lathe alignment; does it cut straight with chucked work unsupported by a center? a lathe that will turn straight and still turn non flat facing cuts shows wear on the saddle ways and/or wear on the cross feed. If it does not turn straight or face square both together, it likely needs leveling of the bed. Cross slides are not particularly adjustable, except by re scraping.
 
I just checked it the other day.
No discernable taper over 6.5" unsupported.
Maybe a facing cut would more accurately tell me if I'm out if square?
 
I checked run-out on the taper and it was very slight, .0001"-.0002".
On the face it is .001"
Any insight on what this means?
 
It probably means that the underside of the carriage and the bed ways are worn, or the cross slide ways are worn, or both; re scraping the cross slide ways to restore the alignment would be the minimum measure to restore the alignment for facing square to the axis,
 
Lathes are often set up from the factory so they will produce facing cuts slightly off square, on purpose, with the center of the cut deeper than the outside diameter. Often that facing cut is going to be a stand or we otherwise want contact on the outside edges instead of at the center, which would make it rock on what it is attached to. However, it should be a very small amount off square, perhaps .001" in a two or three inch cut. Sometimes we want the cut truly flat across the face, and that can be addressed by making the cut with the compound after dialing it in with an indicator first to get it square, if the cut is not longer than the compound travel. A parallel across the hollow faced work can be used to dial it in, then the cut made with the compound. The lathe can be set up to face dead nuts square across the work, but then any slight imperfection will cause issues with mating the face to a flat surface.
 
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Interesting. Thanks Bob
I just took a facing cut on a Ø 6".
Up to the center there was .0008" and past that an additional .001".
I'm going to go back out monkey around some. I might change to my 3J and try again.
I tried the cut first with my modified 1.25" tool holder. It cut nice until about one third in then got bad, rough.
Not sure what was going on there but maybe the piece moved a little.
 
Interesting. Thanks Bob
I just took a facing cut on a Ø 6".
Up to the center there was .0008" and past that an additional .001".
I'm going to go back out monkey around some. I might change to my 3J and try again.
I tried the cut first with my modified 1.25" tool holder. It cut nice until about one third in then got bad, rough.
Not sure what was going on there but maybe the piece moved a little.
I would suspect a minute breakdown of the cutting edge to account on the finish going rough; it does not take much.
 
Could be yes.
It is a negative insert also although that doesn't matter I don't think.
 
Only problem with facing with the compound is that
Lathes are often set up from the factory so they will cut slightly off square, on purpose, with the center of the cut deeper than the outside diameter. Often that facing cut is going to be a stand or we otherwise want contact on the outside edges instead of at the center, which would make it rock on what it is attached to. However, it should be a very small amount off square, perhaps .001" in a two or three inch cut. Sometimes we want the cut truly flat across the face, and that can be addressed by making the cut with the compound after dialing it in with an indicator first to get it square, if the cut is not longer than the compound travel. A parallel across the hollow faced work can be used to dial it in, then the cut made with the compound. The lathe can be set up to face dead nuts square across the work, but then any slight imperfection will cause issues with mating the face to a flat surface.
The problem with facing with the compound is that the surface finish will likely suffer, as it is difficult to maintain a regular feed by hand and there is a tendency for hand feeding to slightly move the compound from side to side, causing the tool to alternately dig into the work and pull away; there is a fine line between ease of feeding and a tight slide, stable but difficult to feed.
 
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