Why didn't anyone warn me about mag scales on the DRO?

pontiac428

pontiac428

John Newman
H-M Lifetime Diamond Member
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Okay, I'm not holding anyone accountable for this, I attended all of my physics classes sober so it's all pretty obvious. But I had something happen today that justifies dumpster slamming magnetic scales in favor of opticals.

There I was, milling away joyfully and producing a nice part today, when the hot blue steel curls became unbearable on my skin. I set up my chip shield and finished the part. As I was tearing down, I removed the mag base on my chip shield, an aging Starrett with a real weak pull. While moving with the magnet above the table, I noticed the displays fluttering everything to the right of the decimal place on my DRO. I cussed an incantation and waved the magnet all up and down around my mill, watching the numbers change. It would do it 24" away from the scale or sensor somewhat predictably as I moved it up, down, left, and right through the air over the table.

The mag scale readers are metallic and the cables are metal shielded. They may have ground loops, which would explain the sensitivity to the field. To be honest, I don't care why the DRO responds so much, it's the fact that the numbers change in response to a common mill table tool's presence that I can't abide. I don't run the mill on faith, I run it on confidence. If I have to rely on faith that the local magnetic fields are stable in order to make a part, I'm tapping out.

This has me on Alibaba measuring up for some optical scales right now. It's not sitting easy with me. Have any of you observed such a thing?
 
This is one of the downsides to magnetic scales. In fact, most manufacturers warn not to use magnetic indicator holders too close to the scales, and not to store them on the mill table. For that reason, I mounted my X scale on the back of the table. Still from time to time one of the digits may flutter if I get a magnetic base too close. No harm done. Once the magnet is moved the scale settles down and all is well.
 
Another reason I'm happy with my capacitive scales.
 
pontiac428 said:
Okay, I'm not holding anyone accountable for this, I attended all of my physics classes sober so it's all pretty obvious. But I had something happen today that justifies dumpster slamming magnetic scales in favor of opticals.

There I was, milling away joyfully and producing a nice part today, when the hot blue steel curls became unbearable on my skin. I set up my chip shield and finished the part. As I was tearing down, I removed the mag base on my chip shield, an aging Starrett with a real weak pull. While moving with the magnet above the table, I noticed the displays fluttering everything to the right of the decimal place on my DRO. I cussed an incantation and waved the magnet all up and down around my mill, watching the numbers change. It would do it 24" away from the scale or sensor somewhat predictably as I moved it up, down, left, and right through the air over the table.

The mag scale readers are metallic and the cables are metal shielded. They may have ground loops, which would explain the sensitivity to the field. To be honest, I don't care why the DRO responds so much, it's the fact that the numbers change in response to a common mill table tool's presence that I can't abide. I don't run the mill on faith, I run it on confidence. If I have to rely on faith that the local magnetic fields are stable in order to make a part, I'm tapping out.

This has me on Alibaba measuring up for some optical scales right now. It's not sitting easy with me. Have any of you observed such a thing?
Click to expand...
You didn’t mention the readout fluttering while you were running the mill with the mag base stationary, only while you waved the mag base around. You also didn’t mention if your part was on size or not when finished. Does the readout flutter while the mag base is stationary and the table is moving? Or only when you wave the mag base around?

Tom
 
pontiac428 said:
Okay, I'm not holding anyone accountable for this, I attended all of my physics classes sober so it's all pretty obvious. But I had something happen today that justifies dumpster slamming magnetic scales in favor of opticals.

There I was, milling away joyfully and producing a nice part today, when the hot blue steel curls became unbearable on my skin. I set up my chip shield and finished the part. As I was tearing down, I removed the mag base on my chip shield, an aging Starrett with a real weak pull. While moving with the magnet above the table, I noticed the displays fluttering everything to the right of the decimal place on my DRO. I cussed an incantation and waved the magnet all up and down around my mill, watching the numbers change. It would do it 24" away from the scale or sensor somewhat predictably as I moved it up, down, left, and right through the air over the table.

The mag scale readers are metallic and the cables are metal shielded. They may have ground loops, which would explain the sensitivity to the field. To be honest, I don't care why the DRO responds so much, it's the fact that the numbers change in response to a common mill table tool's presence that I can't abide. I don't run the mill on faith, I run it on confidence. If I have to rely on faith that the local magnetic fields are stable in order to make a part, I'm tapping out.

This has me on Alibaba measuring up for some optical scales right now. It's not sitting easy with me. Have any of you observed such a thing?
Click to expand...
What machine?

I wonder about decoupling the scales and read heads with some non ferrous or plastic would lessen this effect.

On my mini machines I have used magnets exactly twice and that was enough.

Seeing the material in the lathe chuck attract all the nearby chips and the same with the ring light on the mill was enough.

Too small/not enough mass for magnets to be used on them.
 
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