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Lathe dro readings wrong.

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terry callaghan18/09/2021 13:14:51
237 forum posts
10 photos

Hi out there. I fitted a dro to my lathe sometime back, and today I tried to finish the set up and see how good or bit it works. Well it’s not good. I have checked the scale runs with a dro and they run true on both axis. I then measured the movement on the cross slide of the lathe moving it into the center 35mm on the dro. Then I measured the movement of the cross slide with a digital vernier gauge and the measurement was only 17mm. Something is way off. I lost the manual and can’t find one on the internet. It’s a cheap Chinese dro. Anyone have any views. Thanks.

Dave S18/09/2021 13:20:07
362 forum posts
90 photos

35mm would be the diameter reduction for 17.5mm of movement.

Sounds like your DRO is telling you how much smaller the bar will be vs how far the cross slide has moved


not done it yet18/09/2021 13:24:58
6733 forum posts
20 photos

I might suggest there is slop in the cross slide, it ‘slewing’ slightly, dependent on which way it is driven?

The finished cut diameter will depend on the cutter geometry.  A change of cutter position should be undertaken after a physical measurement of the diameter in order to finish at the desired dimension.  That would be (or should be) precise, provided cutting feed rate and depth of cut is not altered.  

There is no guarantee of finished dimensions if the lathe operating parameters are changed between physical measurements.

Edited By not done it yet on 18/09/2021 13:32:27

John Baguley18/09/2021 13:38:05
503 forum posts
54 photos

Sounds like you have the DRO set to read diameter rather than radius. There should be a D/R button to change between the two.


not done it yet18/09/2021 14:01:41
6733 forum posts
20 photos
Posted by John Baguley on 18/09/2021 13:38:05:

Sounds like you have the DRO set to read diameter rather than radius. There should be a D/R button to change between the two.


That will depend on the dro. Mine are simple, stand-alone items - although they can also indicate on a separate reader head. That does not explain the 0.25/0.5/1mm difference in expected movement in practice.


Edited By not done it yet on 18/09/2021 14:04:10

terry callaghan18/09/2021 14:21:04
237 forum posts
10 photos

Thanks chaps, that sorted it. Sometimes you just can’t see the answer to an easy answer to the problem.

Dave S18/09/2021 15:55:55
362 forum posts
90 photos

I assumed the 0.5mm difference was down to slightly dodgy measuring technique with the digital very-near


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