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DRO calibration?

pip9ball

Plastic
Joined
Jan 30, 2023
Hello All -

I recently purchased a cheap DRO from Vevor (https://www.vevor.com/linear-scale-...-dro-encoder-for-milling-lathe-p_010132284154) and I'm experiencing an issue where my DRO measured value is different than the actual part diameter measured.

I've reviewed the manual and calibrated the X axis using an indicator along with a 1-2-3 block and confirmed that moving my cross-slide 3.0" matches with my my DRO x value says (3.0002").

My usage:

Make a skim cut on piece and measure diameter with micrometer. Let's say it's 1.32". I then enter X -> 1.32 Ent into DRO. Now when I move my cross-slide until DRO reads 1.295" and make another cut, however when I measure the actual piece it is always much smaller (like 1.282"). I've tried changing the modes from Radius to Diameter and that doesn't seem to affect anything.

Is it possible that tool deflection could be causing these errors?

Thanks,

Phil
 
Another thing to check is whether the cross slide moves at some point due to starting and stopping the lathe. Even my 10EE cross-slide will slip a couple tenths when starting just due to the tiniest amount of springiness in the screw, nut, and casting assembly.
 
What material are you cutting, and what are you using for a cutting tool? (HSS, sharp edge positive rake carbide, strong edge negative rake carbide?)
Does the DRO give the same reading at the beginning of the pass and the end of the pass? If not, your cross-slide is pulling forward during the cut. You may need to be more careful about taking out the cross-slide backlash as you dial in your DRO setting, including the skim cut where you set the DRO X value.
Also check your compound slide. If vibration is making the compound crank rotate, that can completely invalidate your DRO readings.
Tool deflection usually leads to the part measuring larger than the DRO setting would suggest. In this case, if you leave the cross-slide exactly untouched and run the carriage back and forth for some "spring" passes, the part will get a bit smaller. How much smaller will depend on how much deflection there was in the original skim pass you used to set the DRO.
If your DRO X scale is not mounted precisely parallel to the cross-slide travel, you will get a consistent cosine error. A given actual motion of the cross-slide will read on the DRO as a longer motion. Again, this would tend to give you oversized parts from dialing in a DRO setting, not smaller ones. And you checked for this, with your 123 block.
I am afraid most of the things I can think of that would give you smaller parts than expected are related to unpracticed technique or bad tooling.
 
What material are you cutting, and what are you using for a cutting tool? (HSS, sharp edge positive rake carbide, strong edge negative rake carbide?)
Does the DRO give the same reading at the beginning of the pass and the end of the pass? If not, your cross-slide is pulling forward during the cut. You may need to be more careful about taking out the cross-slide backlash as you dial in your DRO setting, including the skim cut where you set the DRO X value.
Also check your compound slide. If vibration is making the compound crank rotate, that can completely invalidate your DRO readings.
Tool deflection usually leads to the part measuring larger than the DRO setting would suggest. In this case, if you leave the cross-slide exactly untouched and run the carriage back and forth for some "spring" passes, the part will get a bit smaller. How much smaller will depend on how much deflection there was in the original skim pass you used to set the DRO.
If your DRO X scale is not mounted precisely parallel to the cross-slide travel, you will get a consistent cosine error. A given actual motion of the cross-slide will read on the DRO as a longer motion. Again, this would tend to give you oversized parts from dialing in a DRO setting, not smaller ones. And you checked for this, with your 123 block.
I am afraid most of the things I can think of that would give you smaller parts than expected are related to unpracticed technique or bad tooling.

Thanks for the pointers, I replaced the insert in my tool and reset the height. Things are lining up now :-)
 
Another thing to check is whether the cross slide moves at some point due to starting and stopping the lathe. Even my 10EE cross-slide will slip a couple tenths when starting just due to the tiniest amount of springiness in the screw, nut, and casting assembly.
Thanks for the reply. This was one of the first things I checked and I don't see movement.
 








 
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