Another obligatory New PM-833TV and PM-1340GT Ordered!

OK I’m very confused. Test bar shows my headstock is aligned. Still don’t understand why I would get the measurements I got on the face of my 3 jaw from front to back.
 
Maybe a little piece of junk between the chuck and the spindle? My guess is you would have noticed that right off the get go. I'm just guessing, looking forward to what some of the experts have to say.
 
Just for fun said:
Maybe a little piece of junk between the chuck and the spindle? My guess is you would have noticed that right off the get go. I'm just guessing, looking forward to what some of the experts have to say.
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Turned the chuck 120 degrees 3 rimes and saw the same.
 
Maybe I was just getting too much deflection on the cuts.
 
Kind of sounds like the cross slide is not parallel to the chuck. If I remember correctly somebody with a 1236T was complaining about that. Don't quote me on that though I may be incorrect.
 
If you are making a test cut 12" long and it is unsupported on the other end, then you will cut a taper unless you are using 3 or 4" stock, there is always going to be some deflection from cutting the further away from the chuck. I would suggest doing a two ring test taking very light cuts with a sharp cutter. In addition even if you are using a live center to support the other end of a work piece and it is on center, you may have to slightly tweak the tailstock position to get the same diameter across the piece (we are talking under 0.001") and depends on the material, DOC, etc. The cross slide position should not change, its position is dictated by the ways, so unless they are worn or twisted that should not be a factor. The cross slide can move slightly if not locked or the gibbs are not set correctly, but usually we are talking less than 0.001" in my experience.
 
Today I put my MT5 ground test bar between centers after confirming my headstock alignment was good, and dialed in my tail stock. The GT1340 tailstock is a tad finniky, but I started with a dial test indicator on the tailstock quill, nearly fully extended and locked down, and dialed in the parallelism to the bed ways using the rear most adjusting screws. Next I swept back and forth on the test bar to get the center dialed in using the opposing side adjusting screws. I had to back off the rear screws just a tad so the tailstock would shift smoothly in the X axis, and then button everything up once adjusted to ensure it was all tightly locked in place. A 3 casting design may make each axis of tail stock adjusting easier, removing dependancies between the X axis, and Axial alignment. but it just took a bit of back and forth and hopefully I am good for a while there.

When sweeping the Z travel, I noticed my DTI would show about a thou in variance based on where the wheel was, so I suspect there is some slight runout or eccentricity of the feed gear and the straight gear mounted to the bed, so I slightly tightened the rear apron gibs to minimize the pulse. Did a slight adjustment on the cross slide gib, and the compound gib, and buttoned everything up.

I just started making the Hemingway sensitive knurling tool, so I can now continue with that build. I think I may turn a live center nose extender so I can do a better job of getting my cutting tools closer to small diameter parts. Question for those who have the PM live center. How do you take it apart for maintenance?
 
Everything I put in my 3 jaw chuck comes out horrible.Did some more testing today, and it seems that everything I put in the chuck favors Jaw 2 by .003 - .006" repeatably.

I seem to be cutting about a .004" plus taper when doing any operation with my 3 jaw. In other words, my cut starts fine near the live center, and gets narrower as I approach the chuck because it is holding every part eccentric to center. Thats pretty damn annoying. Without a tool post grinder, I am not sure there is much I can do about it...I had a .004" taper on a 3 inch part.

Edit - After thinking about the above, that should not be turning a taper. I am at a complete loss. Got my test bar directly in the MT5 less than a half a thou over 12 inches, I then put that bar in and aligned my tailstock. Anything I cut is narrower towards the chuck than it is near the tail.

I think my next step needs to be inspecting level incrementally down the bed to check for twist... but I still don't understand why I can indicate down 12" of test bar accurately if I had twist.
 
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Try it with a 4J independent, sounds like it is an issue with the 3J chuck, they can have a TIR issue, but also a skew or axial deflection issue.
 
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