The Shop > Electronics & IC Programing

DIY bluetooth DRO for my mill

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vtsteam:
I had to shorten the Y scale by 4" to fit my mill. That was easy to accomplish with just a hacksaw. Then I reversed the end brakets so that the back of the reader head faced out, I drilled and tapped the new new Y axis mount, which I'd painted last night. Here's the assembled scale and mount:

vtsteam:
I made a fixed bracket for the read head and mounted that to the mill base. With that the Y scale installation was complete.

vtsteam:
I did a quick test of the Y axis using the same resolution setting I had for the X. I got different results which surprised me until I remembered that the X calibration was against a DTI set on the table and bearing against the quill. This time with the Y, I was just looking at the dial readings on the crank. I then checked the X against dial, and got a similar result. So that begs the question, which is corret, the cheap DTI, or the dials? Or neither.

I'm in need of a standard......

PekkaNF:
Yesh...standards are good. Do you have two micrometers that are larger than 1"? Their calibration rods are remarkably accurate. I also have found that bearings are made to very exacting standards and their tolerances are according to published tables and nominal diameters are comfortable numbers.

other thing: Those scales are capacitive, right? I have used the very little, but I think that they are very sensitive to scale-head distance variation....therefore the head should "float" and no load to twist or influence perpenticular to scale should be present. In normal caliper that is no problem, because the body is pretty effective guide rail.

Pekka

vtsteam:
Thanks Pekka. I do have a big micrometer, I was thinking I'd have to make a bar up with it, but if I have a cal rod with it, I'll use that. In mounting, I've been very careful not to bind the scales in any way, but we'll see.

I think friction or binding error would show up as scale reader backlash, in other words not returning to the same point after a traverse and then reversal, vs calibration error which would show up as a one directional measurement error.

The main thing I'll be looking for, after calibration adjustment would be inconsistencies for traverses of varying lengths and their returns. That should show what the limits are.

I think I remember reading something somewhere that the leadscrews on these mills is actually a metric approximation of inches, and the inch dials will show some error, but I'll figure out -- will also check my DTI, out of curiosity.

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