Hope you don't mind me asking here, got a glass scale issue, I think

[WobblyHand]

I seem to have an issue with the scale not counting correctly. It appears to skip or lose counts. Today, when drilling some holes on my PM25MV mill, it seemed like there was a region where the scale wasn't updating, like it normally does. This miscount (or skipped count) ended up making me not drill the holes in the right place. When I returned to 0 it was in the wrong place. Ie, not directly over the edge of the part. It seems to loose counts going in both directions. To make this more irritating, this is my second attempt at making this piece. Both times, the holes ended up in the wrong spot. Out of 165.8mm of travel, my DRO only recorded 159mm. This time, I am positive it is the DRO, not me. The previous time, well, it might have been the operator, but it could have been the DRO is skipping counts. The feed rate in both cases was by hand and not very fast. 6 months ago, the DRO seemed to be fine, and I observed no problems even with a power feed.

Is this a typical dirty glass scale kind of problem? I looked underneath and saw some swarf up by the seal, but not a heck of a lot. Plan to remove the x scale and read head from the mill and try to clean it, but first I guess I will check for any loose fasteners. I'm out of my element here, and thought I ask others with a lot more knowledge on these scales. If this is the wrong place to post, I apologize. Thanks.

 

[mchasal]

Do you have multiple scales? If so, does it only manifest on one of them? If so, that would probably rule out TouchDRO being the problem. You could swap the scale connectors and see that the problem follows the scale which would confirm that it's the scale itself.
I have magnetic scales, so not sure what glass scale problems would cause this, but debris in there does seem like a possibility.

 

[WobblyHand]

Do you have multiple scales? If so, does it only manifest on one of them? If so, that would probably rule out TouchDRO being the problem. You could swap the scale connectors and see that the problem follows the scale which would confirm that it's the scale itself.
I have magnetic scales, so not sure what glass scale problems would cause this, but debris in there does seem like a possibility.

Yes, I have multiple scales (3). No, I am not using TouchDRO. I did not know about TouchDRO when I bought the mill with DRO. That's why I apologized for the post in this sub-forum. However, I was trying to access people, such as yourself, that have had good hands on experience with DROs.

I have not seen this error on the Y scale, or Z scale. I strongly suspect swarf, but wanted to see if there were any other issues or physical things that can cause this sort of problem. Or at least receive pointers on removing the scales and head without ruining alignment. Don't want to make things worse than they are...

 

[markba633csi]

If it seems to be a certain region then it must be the scale. Can't be anything else.
Unless the read head cable is getting caught or pulled on then contamination got into it somehow

 

[WobblyHand]

If it seems to be a certain region then it must be the scale. Can't be anything else.
Unless the read head cable is getting caught or pulled on then contamination got into it somehow

It's near the center of the scale. Also seems to me that the cables are tied a bit tight. Tidy is good, tight is not, since it strains the wire and connections. I will have to redo the X anyways, since I have to cut all the tie wraps to get it out to clean. Just grabbed the JIS screwdrivers for the job. Chinese cross-head screws are usually JIS. A Philips screwdriver will cam out and strip the heads, learned from experience.

 

[ycroosh]

I seem to have an issue with the scale not counting correctly. It appears to skip or lose counts. Today, when drilling some holes on my PM25MV mill, it seemed like there was a region where the scale wasn't updating, like it normally does. This miscount (or skipped count) ended up making me not drill the holes in the right place. When I returned to 0 it was in the wrong place. Ie, not directly over the edge of the part. It seems to loose counts going in both directions. To make this more irritating, this is my second attempt at making this piece. Both times, the holes ended up in the wrong spot. Out of 165.8mm of travel, my DRO only recorded 159mm. This time, I am positive it is the DRO, not me. The previous time, well, it might have been the operator, but it could have been the DRO is skipping counts. The feed rate in both cases was by hand and not very fast. 6 months ago, the DRO seemed to be fine, and I observed no problems even with a power feed.

Is this a typical dirty glass scale kind of problem? I looked underneath and saw some swarf up by the seal, but not a heck of a lot. Plan to remove the x scale and read head from the mill and try to clean it, but first I guess I will check for any loose fasteners. I'm out of my element here, and thought I ask others with a lot more knowledge on these scales. If this is the wrong place to post, I apologize. Thanks.

What you are describing is more similar to DRO skipping counts. Dirty scale manifests is as a dead spot, but the scale is usually pretty repeatable. I.e. the dead spot prevent pulses both ways, so you should be getting back very close to 0. In your case 7mm is a LOT, though. Missed pulses accumulate over hours of use to fractions of a mm (thus, very hard to notice). I would check the wiring first. A broken wire or a loose connection can cause large discrepancy, and it can be happening in one spot (i.e the cable gets bent at just the right angle, etc...)

 

[WobblyHand]

What you are describing is more similar to DRO skipping counts. Dirty scale manifests is as a dead spot, but the scale is usually pretty repeatable. I.e. the dead spot prevent pulses both ways, so you should be getting back very close to 0. In your case 7mm is a LOT, though. Missed pulses accumulate over hours of use to fractions of a mm (thus, very hard to notice). I would check the wiring first. A broken wire or a loose connection can cause large discrepancy, and it can be happening in one spot (i.e the cable gets bent at just the right angle, etc...)

The cables are tied up pretty tight, in my opinion, on this mill. I ordered the mill with the DRO installed. Next time, I'll install a DRO myself.
Thanks for your recommendation. I will check the wiring harness in its range of motion.

It feels like missing or skipping counts as you say. It's no good to have a wandering datum...

 

[JFL4066]

Since you did not install the scales, maybe there's an alignment issue? Use an indicator to verify the read head is running parallel to the scale. Could be bowed or angled causing the read head to twist or too much force of the head to scale contact. Just my 2 cents.