Probing direction error compensation

[adatesman]

I would think you would want a more quality probe for digitizing. DP4 is less than a Renishaw.
That said, provide the documentation & examples for Mach's compensation you refer to. (videos, pictures, instructions, explanations etc.)

Marty

I forget the Mach Plugin I saw when digging into this a couple weeks back, and chances of finding the YouTube video I watched are slim (I don't recall which computer/phone/ipad I was on). I don't think this is the one, but does the same thing: http://www.craftycnc.com/probe-it-wizard-mach3/

[adatesman]

Given that the error is apparently consistent and isn't rotationally symmetrical, I think you can conclude that there is some physical inconsistency at work within the probe itself. In the interests of science (and if you could be bothered), you might be tempted to dismantle it and attempt a root cause analysis.

There are no black arts at play here, so the cause is likely to be discernable if you know what you are looking at. Given how these things are constructed, the most likely explanation seems (to me) to be that the spring isn't exerting an even force on each of the three pins, possibly due to it not being closed and ground consistently. But that's just a guess. Perhaps you should attempt to measure the force in each of the 3 primary directions for starters.

You'll note that Drewtronics doesn't seem able to show any specs for the probe beyond a rather broad claim of "~0.001" accuracy", whatever that means. As we know trilobe probes aren't symmetrically consistent, there's more to an accuracy spec than that. There may be a clue there for you.

There seems to be a tendency to believe that backlash compensation and probing compensation are some sort of magic solution. When your machine is displaying backlash of +/-0.003", the solution might be a bit more involved than trying to bring some form of fancy software compensation to play.

I agree, to a point. I've run quite a few Wall Following cycles with the same Spindle/Probe orientation, and it repeats surprisingly well. Just off, depending on angle. Which means a good fit for probing compensation.

Had the Drewtronics apart and was well made and spring closed on the ends. I did not notice whether ground and do not have a pic of that, as I was only interested in seeing the alignment of the pins in relation to the lobing in the error I'm seeing. Will take it apart again sometime soon, but I'm in the middle of aligning a larger diameter, thicker stem probe to see if maybe the skinny stylus shank on the 1mm probe is confounding things.

[adatesman]

The new Centroid KP-3 being currently tested, should be much better than the Drew probe, and other low cost Kinematic probes.
Just be patient while we get through testing....
Marty

Indeed, something better may be the solution. For now, I can just mount my part on the rotary and only probe one direction then rotate for the next point, thereby eliminating both backlash and kinematic error. Long term though, probe compensation would be the ideal solution since this one repeats so well provided rotational alignment stays consistent.

[adatesman]

BTW, thanks All.

Working on it tonight, but won't be able to get back to it for a week or two after that.

[adatesman]

Ah, seems I had a pic of how well it repeats on the other computer. This is 3 runs of Wall Following. Green circle is nominal, two red circles max/min. In a single orientation, it's good to ~0.001 and simply needs kinematic compensation.

[frijoli]

The new Centroid KP-3 being currently tested, should be much better than the Drew probe, and other low cost Kinematic probes.
Just be patient while we get through testing....
Marty

Long term though, probe compensation would be the ideal solution since this one repeats so well provided rotational alignment stays consistent.

How would the machine know what orientation the probe is in? Most industrial cnc machines do not incorporate probe compensation for a reason. Acorn is based on professional CNC controls, but introduced to the hobby market.
Seriously, the probe is supposed to be more accurate than the machine tool. I personally don't want the compromise; I suspect you could write a macro?

[adatesman]

duplicate post. Sorry.

[adatesman]

The new Centroid KP-3 being currently tested, should be much better than the Drew probe, and other low cost Kinematic probes.
Just be patient while we get through testing....
Marty

Long term though, probe compensation would be the ideal solution since this one repeats so well provided rotational alignment stays consistent.

How would the machine know what orientation the probe is in? Most industrial cnc machines do not incorporate probe compensation for a reason. Acorn is based on professional CNC controls, but introduced to the hobby market.
Seriously, the probe is supposed to be more accurate than the machine tool. I personally don't want the compromise; I suspect you could write a macro?

Spindle orientation has been a thing for a very long time. At least 1980s by my recollection.

Mount the probe in a holder, Control aligns ATC and spindle. Iirc, that’s the reason for the dimple in CAT holders. Or maybe differing key widths. I forget.

In any event it repeats, so can be compensated for in software. I'm currently ~3000 data points into ~6000 for the evening, and will post results once I have them.

As for the implication I’m unfamiliar with industrial machinery, last machine I bought before this Taig was a $1.2million Cincinnati with laser interferometers on 3 of 5 axes. Was more accurate than our Starrett CMM. Not quite up to customer's Zeiss. Was an oddball in a shop full of Mazaks, but Mazak didn’t make anything big enough at the time. IIRC, the Cincinnati was 100" between the columns, table 200"+ inches. Mazak maxed out with their 5 sided V-60, which only had 60" x 120" pallets. That one was ~$800k, and VP of Mazak came to christen its installation as it was the first in the US.

Which is to say, kindly don’t talk down to me. Acorn is cheap, and directed to the hobby market.

As such, users will have hobby probes. I’ve spent a silly amount of time enumerating the error in this probe, in hopes a good-enough software compensation solution will be provided.

As I mentioned, I can work around this with a macro and rotary. Better solution is probe compensation, given the market.

[frijoli]

Long term though, probe compensation would be the ideal solution since this one repeats so well provided rotational alignment stays consistent.

How would the machine know what orientation the probe is in? Most industrial cnc machines do not incorporate probe compensation for a reason. Acorn is based on professional CNC controls, but introduced to the hobby market.
Seriously, the probe is supposed to be more accurate than the machine tool. I personally don't want the compromise; I suspect you could write a macro?

Spindle orientation has been a thing for a very long time. At least 1980s by my recollection.

Mount the probe in a holder, Control aligns ATC and spindle. Iirc, that’s the reason for the dimple in CAT holders. Or maybe differing key widths. I forget.

In any event it repeats, so can be compensated for in software. I'm currently ~3000 data points into ~6000 for the evening, and will post results once I have them.

As for the implication I’m unfamiliar with industrial machinery, last machine I bought before this Taig was a $1.2million Cincinnati with laser interferometers on 3 of 5 axes. Was more accurate than our Starrett CMM. Not quite up to customer's Zeiss. Was an oddball in a shop full of Mazaks, but Mazak didn’t make anything big enough at the time. IIRC, the Cincinnati was 100" between the columns, table 200"+ inches. Mazak maxed out with their 5 sided V-60, which only had 60" x 120" pallets. That one was ~$800k, and VP of Mazak came to christen its installation as it was the first in the US.

Which is to say, kindly don’t talk down to me. Acorn is cheap, and directed to the hobby market.

As such, users will have hobby probes. I’ve spent a silly amount of time enumerating the error in this probe, in hopes a good-enough software compensation solution will be provided.

As I mentioned, I can work around this with a macro and rotary. Better solution is probe compensation, given the market.

I wasn't talking down to you. Point I was making was that it's not important to high end tools, nor in my opinion should it be to Acorn buyers. Fix the known issue, not the perceived one. Sorry if you took it otherwise.

[slodat]

Spindle orient is, and has been for some time, a function of the spindle drive and the spindle encoder. This requires a drive that has an orient function built in, which is not what most hobby users are using in their Acorn builds. I really like your idea of probe compensation. It's clear you know how to assess the situation. Perhaps we will get it.