Why Can't I get my DTI to Repeat

Okay update. I tried what BenW suggested and tightened the preload collar. Noticabley harder to rotate by hand. The wonky abrupt movements have disappeared and actually get a repeat on the first rotation, then .0003" the next so I would say it is better. I may go a little tighter and see what happens. I'm tempted to run the machine as I can still get almost two rotations on freewheeling after spinning by hand. Try for a vid soon.
 
Another quick update.
I went slightly tighter yet.
I moved a little towards the TS on the test bar to get a little more movement. Zeroed the DTI by cross slide, zeroed the DI by the dial. First rotation 0, next .0004", next zero then .0005" high, zero and back and forth to .0005". At least now it is more consistent. I may pull the chuck off and check the spindle again.
 
When you tighten spindle bearings, it is a good idea to read the machine manual for how to approach and carry out the adjustment. When you test the spindle after making bearing adjustments, run the spindle and check for excess heat in the bearing areas at both ends of the head stock. Start at a fairly low speed, and then gradually speed it up. It takes quite a bit of time before the heat gets transferred to where you can feel it with your hands, and the bearings may be damaged by then if you do not do the testing properly, taking your time to do it right. The spindle should be fairly easy to turn by hand, even when preloaded properly. If things are not going well with the preload adjustment, the bearings may be damaged. Take it apart and inspect them.
 
No manual unfortunately.
You mean take it apart before I run it?
 
ddickey said:
No manual unfortunately.
You mean take it apart before I run it?
Click to expand...
Only take it apart if you have strong evidence of probable bearing problems. I see in post #56 it is an Acra 13x40. There are certainly manuals available free here or online for similar lathes sold under other brand names. Any of them will give you an idea of how to check the spindle bearings properly. I have the manual for my Kent KLS-1340-A lathe, but only on paper, unfortunately. Adjusting spindle bearings is about the same for most all lathes with the same type bearings.
 
Okay guys.
What i ended up doing was to loosen the preload collar 1/2 turn and beat the spindle towards the TS end.knocked it loose and it just spins super free. Then the numbers went all kiddywampus. Slowly re tightened checking run out. Got slight drag and the numbers quited down to almost nothing. with my .0005 DTI I estimate .00025" TIR. It seems to repeat quite okay but still that second rotation is the dead on and most every rotation. I've probably been running to light of preload for years.
Any other suggestions let me know.
Thanks for everyone's help.
 
Bob Korves said:
Only take it apart if you have strong evidence of probable bearing problems. I see in post #56 it is an Acra 13x40. There are certainly manuals available free here or online for similar lathes sold under other brand names. Any of them will give you an idea of how to check the spindle bearings properly. I have the manual for my Kent KLS-1340-A lathe, but only on paper, unfortunately. Adjusting spindle bearings is about the same for most all lathes with the same type bearings.
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Thanks Bob I'll check for similar models.
 
Ran for twenty minutes in the second highest speed. Barley any heat. Found the preload process for a Grizzly.
 
So, this is resolved? The indicators repeat?
 
Mike,
It is ten times better. Not perfect but I think I can tweak the preload a little more.
I got three rotations to return to zero, next was a tenth above zero and next was a tenth or two below. So it is very close.
 
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