DRO drifting

No I have not swapped the cables round yet. I installed an earth cable last night so I plan to see if the DRO drifts overnight before going any further with the investigation. I'm not planning on using the machine this evening but I will do a test cut just to see if it has drifted at all. I'm hoping that all is well and it was the ground that was causing me the issue however if it has drifted I will switch the cables round, set a size and leave it again to see if it drifts.

Frustratingly I don't know over what time period it drifts - to be honest I've never really paid it much attention other than re-setting the size before each use. I don't use the machine every day so it could happen overnight or it could happen over the space of a few days.
 
How long have you owned this DRO system? The drift could be a sign of impending failure of an internal part, such as the internal crystal oscillator.
Also, have you tried tapping on the unit to try and duplicate the failure?
Mark
 
I bought this system new just under a year ago. I'm not entirely sure who manufactures it - it's of Chinese origin and is branded as a Warco unit (UK's version of Grizzly and the like I think) and it is fitted to a Warco GH1330 lathe (13" x 30"). Links below if you're interested.

I've not tried tapping the unit but I have given everything a good wiggle to see if anything is loose. So far I've not come across anything.

Since I added the ground the X axis hasn't shifted and the Y has shifted 0.015mm which could easily be due to expansion as suggested above (it has been hot in the evenings and it was cool in the workshop this morning when I checked). I'll check back again this evening and see if it has drifted further or, if it is due to expansion, it's drifted back to 0.

https://www.warco.co.uk/metal-lathe...1322-gh1330-lathe.html#/906-gh1300-gh1330_1ph
https://www.warco.co.uk/digital-readouts-scales-dro/292-digital-readout-scales-glass-optical.html
https://www.warco.co.uk/digital-rea...rco-digital-readout-dro-display-counters.html
 
Hi Guys,

A quick update for you. Apologies that it has taken a while to get back - I've been away with work so haven't had much of a chance to look into it.

After connecting the earth cable I zeroed the X and Y axis and left them for a few nights to see if they drifted and nothing (apart from a very small amount on the Y axis as mentioned in an earlier post which I am putting down to thermal expansion in the machine). Annoyingly when I got back over the weekend I accidentally knocked the cross slide handwheel before getting a chance to check if had drifted while I was away. I re-zeroed the X axis and so far nothing.

So, I believe that, with your help, I have traced the fault to the lack of an earthing cable which has now been rectified.

I will continue to monitor and post back here should anything change but I wanted to give some feedback on the issue and say thanks once again for all of the suggestions above.

Thanks again,
Sam
 
faulty ground can show up during operation on a lathe. Pretty common really as any time you rotate conductive material it generates an electrical field.

Most people never ground there machines but it is a good idea.
 
Finally got my lathe back after it was away for repair with the manufacturer for an unrelated issue. I’ve had a few projects lined up so I started making chips right away but a lot of my non critical dimensions were way off. I don’t usually bother checking these and rely solely on the DRO and I couldn’t understand it. It would appear the drift is back!

When trying to troubleshoot the problem I popped in for a cup of tea and came back to find that it had drifted by four and a half meters! At least that was easy to spot! Most of the time it’s by a mm or two so much harder to spot.

I switched the x and y axis and was still getting the error on the cross slide so I assumed it was the scale itself however this morning I noticed the error on the Y axis (the X axis scale has been removed now so I’m not tempted to rely on it!).

If I touch the cutting tool on a piece of barstock and zero the axis and move the carriage to the far end of the scale then back again it is rarely 0. It can be out by a couple of mm or more each time.

I have verified that the earth is actually earthed with a volt meter and all is good there but now I’m lost! Electrical issues are not my strong point!

Does anyone have any further suggestions?

Thanks in advance!

Sam
 
Had a similar issue with magnetic scales. Called the supplier and described the problem.
He immediately said the reader was bad and sent a replacement.
Solved the problem.
 
I have had the Grizzly version of your DRO on my mill/drill for fourteen years with issues. Intermittent failures can be difficult to track down. Just when you think you have the problem solved, it pops up again.

I'm assuming that you have a two axis DRO and that the y axis is the cross feed (conventionally called the x axis) and the x axis is the carriage movement (conventionally called the z axis). You stated that you were experiencing problems on both scale but different manifestations. Your x axis was jumping to a new value and your y axis experienced a slight drift. You have swapped the cables already and stated
Some thoughts:

Two or more separate failures usually have a common cause. In my experience, unrelated coincidences are rare.

As far as I am aware, the scales do not output absolute position. They sense magnitude and direction of movement and send pulses to the readout with the counter's position registers located within the readout. The readout does retain the last readings if power is lost and reloads them when power is restored. There is a single point on each scale that is an absolute reference point. It can be utilized using the REF function on your readout.

As to thermal expansion, you really should be looking at expansion coefficients of the glass scale and the aluminum backing that it is bonded to in your analysis. Depending on the type of glass used, the expansion coefficient is between 4 and 6 x 10-6 m/m K. Changes in temperature would cause the scale to bow slightly but, since the scale is fixed at either end, not likely to create a positional change significant enough to cause a meaningful shift in the reading. Similarly for the mounting to the lathe.

In troubleshooting, try to eliminate as many possible causes as you can. I would reconnect the second scale and document the anomalies you are seeing.

Based on what you have said, I would suspect an intermittent electrical problem, a bad connection or bad solder joint. In either case, it would most likely require a return for replace or repair. Assuming that you have two different manifestations on the scales, Record the exact problem with each when it occurs, then swap connections. The problem will either go with the scale or remain which will tell you whether the problem is with the scale or the readout.

Armed with that information, contact the vendor and present your evidence. You should still be under warranty. More than likely, the vendor would replace the entire DRO package.
 
Thank you both for your input. It does sound like it's best to get the supplier involved so I've sent them an email with all of the supporting information. Now I just need to remember how I got by before I had a DRO system!
 
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