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Jumpy readout DRO scales on WM16 mill

Unreliable readout figures

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Rik Shaw07/07/2020 11:15:12
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1344 forum posts
364 photos

I have an X and Y cheapo magnetic scale and an XY readout fitted to my WM16 (from WARCO if I remember correctly).

I very soon started to experience the X and Y readings jumping all over the show. After a little experimenting I found that it was happening when I was pressing the ON/OFF button on the mill.

My solution was to isolate the scales and XY sliding readouts from the main casting by mounting them on plastic / nylon blocks and from then on the problem went away----- until the last couple of days, now the gremlin has returned. I have tried all the obvious things like cleaning the scales, replacing USB leads and new lithium cells in the XY readout unit.

Because the "jumping" is still happening when the ON /OFF button is pressed the fault still appears to be an electrical one caused by stray elec fields?? Having found the scales over the years to be indispensible I will either have to identify the cause then fix it OR replace the scales with the more expensive optical things.

So, if you have had a similar problem did you sort it and if so, how.

While I am at it, in the centre of the front control panel on the mill is a caphead screw with an earth sign next to it. I have tried connecting a wire from it to the main X casting but the problem persists. Why is an earth connection here? Being an electrical moron I would have thought that the earth wire in the 3 pin mains plug should be adequate.

Rik

Dave Halford07/07/2020 12:15:11
801 forum posts
8 photos

This sounds somewhat familiar, check the earth connections in the mill power box.

Dave Smith 1407/07/2020 13:47:59
108 forum posts
13 photos

Rik

I got fed up with the same issue, bit the bullet and replaced them with optical scales, never had a problem since. I also fitted them to the lathe about 6 months later. If you do replace think about a 3 axis read out for the mill. You can either then put a scale on the z axis or do what I did, removed the warco quill DRO and replaced it with a 100 mm optical. This means I can now see the read out and it has greater resolution.

Dave

old mart07/07/2020 19:02:00
1825 forum posts
148 photos

I got a cheap ARC readout for the lathe cross slide and it fitted completely out of sight, but I never managed to get it reliable enough because of the emp when the lathe was switched on and off. Even shielding the cable for the readout was not enough. The type was similar to the scale on a digital caliper which I believe is capacitive.

Chris Thorn07/07/2020 22:12:17
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14 forum posts
4 photos

Rik

I had an identical issue with my Wm16b

after head scratching and help on this forum I found out that the machine was not earthed correctly

step 1. Get a multi tester and check from the earth pin of the 3 pin plug of the mill to an exposed metal part of the machine it should be around 0.1 ohms if it’s more than this I would check the earth block in the control panel is bonded to the chassis correctly. Do not use the machine until you have done this.

step 2. If step 1 was ok check the earthing on the socket it’s plugged into.


unfortunately my thread was removed for reasons I still don’t understand?

hope that helps

regards

chris

Rik Shaw08/07/2020 15:45:40
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1344 forum posts
364 photos

I was starting to unscrew the front panel to do more checks as suggested by David Halford and Chris Thorn (thank you both) when for the first time I noticed that the control box seemed a mite wobbly on its mount. Looking underneath I noticed that the silver collar had a tapped hole but nothing in it.

I screwed in a caphead and tightened it and found the box was now rock steady. Also rock steady was the X and Y display where previously it would have often flickered.

screw.jpg

I zeroed the X and Y and spent a quarter hour pressing ON / OFF but was delighted to find the display on both X and Y would not move. I'll call that a result for now and cross fingers that the gremlin has been expunged.

I'll keep Chris and Davids advice on file and follow that through if the mean little beggar decides to return !

Rik

Robert Atkinson 208/07/2020 17:22:37
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698 forum posts
16 photos

Oh dear,
That is an indication that the safety earthing on these machines is not as good as it should be. A clamping screw is not an adequate ground path.

Robert G8RPI.

Ed Duffner08/07/2020 18:21:03
803 forum posts
91 photos

Hi Rik,

I had a similar set of readouts on my WM-16 and simiilar issues as you have described. I believe it was due to the proximity of the USB cables to the machine's mains cable, especially when the cables crossed on or near 90° to each other.

Ed.

Chris Thorn08/07/2020 21:08:29
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14 forum posts
4 photos

Rik

Dont use it until you have checked over the machine with a multi meter ,. Check all Exposed metal parts back to the earth pin of the 3 pin plug .

Better safe than sorry

As Robert says it should not rely on a grub screw for an earth path. I would connect an earth wire from the incoming earth block to the chassis of the machine to be sure

Chris

Andrew Johnston09/07/2020 11:03:37
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5553 forum posts
650 photos
Posted by Ed Duffner on 08/07/2020 18:21:03:

.........especially when the cables crossed on or near 90° to each other.

That's odd, running cables and PCB tracks at right-angles to each other is generally regarded as minimising interference.

Andrew

Rik Shaw09/07/2020 13:13:23
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1344 forum posts
364 photos

Having once again removed the motor cover and front control panel I carried out all the earthing checks as suggested by David Halford and Chris Thorn using my Megger Avo 300 digi meter. The readings were all around .1 ohm so within safe parameters.

Once again thanks to all for your helpful advice ---- especially David and Chris. I hope now that I will find my DRO kit once again, reliable and accurate.

Rik

Robert Atkinson 209/07/2020 14:56:53
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698 forum posts
16 photos

The fact you had issues without the locking screw fitted indicates that it, or the metl it is forcing into contacr is providing the ground connection. This is not acceptable for a safety ground. The safety ground path shoud be properly engineered and not reliant on casual contact between parts. I wonder if it would have passed our test withut the screw fitted. While a DMM will identify gross errors, to properly test safety earthing a bonding test that passes significanr current, around 20A for a small machine tool, is required.

Robert G8RPI.

Rik Shaw09/07/2020 17:10:20
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1344 forum posts
364 photos

Interesting Robert, do you know if these imported budget hobby machines are subjected to a safety earthing bonding test such as you describe before they reach the consumer?

Rik

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