What's acceptable for accuracy?

I just now finished doing the two collar test and alignment on my Logan 400. On the initial test using 1" collars 8" apart the far collar was .006" over. I zeroed a DTI (mounted on the carriage) on the far collar and shimmed the front foot on the tailstock end until the DTI read .003". On retesting the far collar was .0005" under +-.0005. Works slick. Of course, I'd better not move the lathe now...
 
Just curious John, but did you check the height or both collars as well as the -X- position?
 
Tony Wells said:
Just curious John, but did you check the height or both collars as well as the -X- position?
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Do you mean while I was twisting the bed? No. I just intended for the DTI to provide a rough progress indicator so as to minimize the number of cut-measure-shim iterations. I expected to need several. I suppose I would have if I had better instruments.

I'll check it this morning. The setup is still in place and you've got me curious.
 
John Hasler said:
Do you mean while I was twisting the bed? No. I just intended for the DTI to provide a rough progress indicator so as to minimize the number of cut-measure-shim iterations. I expected to need several. I suppose I would have if I had better instruments.

I'll check it this morning. The setup is still in place and you've got me curious.
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Top and bottom are dead on within the accuracy of my DTI with it at about the same place on the carriage as the tool was. With the DTI over on the left of the carriage the top of the far collar reads about .0005" low. I think this means that my ways have a low spot in the busy area: not surprising.

My DTI has .001" divisions so I am eyeballing anything under that.
 
Sounds good, John. I just had a recollection of a Pacemaker I used to run that I was always chasing taper on by moving the tailstock, until one day it occurred to me to check the height. It was 1/8" high on the ts end! Turns out that the ts was not original. Every time I used it, I compensated by side shifting it, but until I got the height right, it was a battle every time. A little careful millwork and I was able to get the height close enough to live with.
 
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