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

[rwm]

I did the same experiment. The numbers change when a magnet is waved nearby. I had to be pretty close with a mag base, say about 3". That could occur in everyday use though.

 

[pontiac428]

I did the same experiment. The numbers change when a magnet is waved nearby. I had to be pretty close with a mag base, say about 3". That could occur in everyday use though.

Exactly my concern, but like I said, everything to the right of the decimal flitters like the dollar tally on a gas pump at 12" or better, and I keep saying the mag base I used is old and weak. In light of that, my worries extend beyond magnets- the mill motor, the power feed, and the RPC all generate dynamic gaussian fields, and I fear they may induce false counts at any time.

Regardless of the reality, the perception of inaccuracy is enough for me. Like setting up a precision rifle, confidence must come first for the system to work at all.

 

[higgite]

After waving a magnet around and then setting it down motionless, say on the table, does the DRO settle down and revert to its previous reading or does it lose its zero?

Tom

 

[Janderso]

Thanks for the input so far, guys. I am interested to see if this inspires you to check your own machines, maybe it's just mine, but maybe it's an unnoticed problem. I did leave out lots of details initially, because I'm questioning all mag scales. Secondary to that is troubleshooting my machine- I can't use a scale I can't trust, that's a hard line in the concrete to cross.


I squared my vise and calibrated the x and y to 1-2-3 blocks with a tenths indicator and a mag base on the head Saturday morning. I was consistently .0004 long (two steps) on y, so linear comp was applied and tested good. Removed the mag base and set up work. During work, I used a mag base for a chip shield. Part came out on size. When I was tearing down is when I saw the numbers flip like a slot machine, an obvious response to a moving magnetic field. The induction must be great enough to trip the trigger in the head, which surprises me. I don't know the effect on the display during power feed or just manual movement, it settles down when static.


This is my Lagun FTV-3 mill, it has a 55x11" table and comes in at almost 4,000 lbs. Sh*t, I put it that way and I feel like an idiot for not going glass to begin with. Oh wait, I did order glass DC10 scales, says right here on my invoice from Ditron, but they sent me 5 mic magnetic. I've never been very excited about these, maybe that's why I never quite finished the job of installing it. The head is a Ditron D80, which I've gotten to like now that I understand it's features. If I trusted it completely, I'd like it more.



I believe that whenever two scales are read, interpolation of either scale becomes possible, with step counts and auto correction becoming possible using the reference track. I don't know so much about the implementation of such techniques in these systems, just what I can read about the technology in general on the web. I am okay with the realities of precision measurement. I have read and referenced the NIST-backed Guide to Uncertainty of Measurement in many papers, so I have realistic expectations of what I can measure and make in my shop, especially without producing some scrap to get there. On the mill, I'd be kidding myself and lying to you all if I claimed to own control over my work to any less than the .001 or .002 that these scales can measure reliably, in the wild, as installed. It's not about precision, it's about a vulnerability that could impact the worth of the numbers displayed on the screen.

Never had an issue with my magnetic scales. Thanks for the heads up though!!

I did have an issue one day when my Y went nuts. I inspected the scale to find a damaged area.
DRO Pros sold me the one scale and got me back up and running.

 

[pontiac428]

After waving a magnet around and then setting it down motionless, say on the table, does the DRO settle down and revert to its previous reading or does it lose its zero?

Tom

It seems to return to zero. I can't shake the last .0004 over 3", which amounts to two steps, even after linear comp (the feature works well). The Y is less sensitive than X, probably because the head is under the table. I'm not too worried about .0004 over 3" in reality, but it's the idea that counts.

 

[projectnut]

Never had an issue with my magnetic scales. Thanks for the heads up though!!

I did have an issue one day when my Y went nuts. I inspected the scale to find a damaged area.
DRO Pros sold me the one scale and got me back up and running.

DRO Pros have some of the better shielding on their Electronica magnetic scales. The only time I’ve experienced interference is when a magnetic base was hanging over the X scale and it went by the reader. Even leaving it at the back edge of the table hasn’t caused any problems

I’ve never had a problem with table power feed or head motor interference

 

[RaisedByWolves]

I'd imagine getting close enough with a magnet would trip up any reader, but I get a lot of changing numbers waving a worn out weak magnet over 12" above the scale. I'm not complaining as if I stuck a neodymium magnet directly to the head, this is an issue with even small changes in the field, apparently.

I only got one of our machines to act up in the extreme, the rest were .0002 of deviation, but the one I started with I could get as high as .016 depending on how I oriented the magnet.

Nothing on the rest of the machine by sticking every magnet I could find on it, waved them around, etc.


These are newall units.

 

[WobblyHand]

Can any of you that are having these problems check if your cable ground is connected to signal ground? Sounds a little bit like some kind of grounding issue. The cable shield shouldn't be grounded at both ends. That can cause a lot of issues. Also check your display end

 

[pontiac428]

I only got one of our machines to act up in the extreme, the rest were .0002 of deviation, but the one I started with I could get as high as .016 depending on how I oriented the magnet.

Nothing on the rest of the machine by sticking every magnet I could find on it, waved them around, etc.


These are newall units.

That's pretty helpful. I wouldn't mind if it were easy to predict or just a matter of not placing mag bases near the heads. I think one should be able to wave a silly mag base over and around the table like an exorcist with a vial of holy water without affecting the reading.

Ditron is not picking up their chat line on Alibaba, I have been trying since Saturday. Must be Chinese Labor Day or nighttime over there or something. I think those folks sleep with their laptops to answer questions at all hours, normally. Actually, I'm being facetious, people deserve weekends and off time. Usually they're on the spot with communication.

I'll look up Electronica, if there is actually something to be gained. With China, you never know, it could be just variations of the same knockoff.

 

[rwm]

Electronica is made in India.