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Author Topic: Probe not matching with edge finder when measuring Y  (Read 720 times)

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Offline jevs

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Re: Probe not matching with edge finder when measuring Y
« Reply #10 on: October 30, 2019, 11:21:34 AM »
I guess my next troubleshooting attempt will be to perform all the calibrations with the probe at a 90 to what I have been doing. Then I can see if the offset values change or stay on the same axis, and then I can do some comparisons to the edge finder to see what/if anything happens different. I need to narrow down if this is due to the probe itself or the machine/ESS/Mach.   

Offline Graham Waterworth

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Re: Probe not matching with edge finder when measuring Y
« Reply #11 on: October 30, 2019, 08:58:13 PM »
Is the error reversed if you probe the opposite face?

Also is there an error in the other axis?

Have you another gauge ring you can measure, the other may be oval


« Last Edit: October 30, 2019, 09:03:35 PM by Graham Waterworth »
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Offline jevs

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Re: Probe not matching with edge finder when measuring Y
« Reply #12 on: October 30, 2019, 11:13:00 PM »
The ring gage is brand new. I bought it for this purpose. It also checks pretty much right on with my calipers to the thousanth and it measures within +/- .00005 with my Mitutoyo inside mic., however I calibrated the mic with the ring also, but double checked it to my my outside mic and my calipers referencing a brand new gage block set. 
So, I kinda have to trust the ring gage is okay. It is certainly more precision than the probe or even my machine I would say.

The error did not change when I rotate the probe 90 degrees and check (without doing a new calibration).
However, I also rotated it 90 and did do the calibration all over. It still had too much error.

I tried changing the Y offset manually in the machine.ini just to see how it reacts. I can dial it in to get the Y- correct, but then I did not check the others (Y+,X+,X-). I just wanted to verify it was working and kinda how it works.

After that, I set things all back up again and rotate the probe to a new position where the LED is facing the operator. This kinda falls where none of the 3 internal pins are in line with an axis. I wanted to see what it does. I centered up the X and Y to the ring gage with an indicator again and recalibrated the probe.

This is what I got this time:
XOffset=-0.001253
YOffset=0.002593
Radius=0.056330

I then did more measurements than other tests to have better data. I probed Y-,Y+,X-,X+ to get zero with the probe at each location followed with a check at each location with the edge finder.

This is what I got with that check.
.200 Dia Edge finder measurements:
Y-    -.1014 (Target -.1000)
Y+    .0958 (Target .1000)
X-    -.0979 (Target -.1000)
X+    .0996 (Target .1000)

So, I consider this still crappy.....
After every calibration I always measured the ring gage with the probe and it was almost always within +/- .0001. It did go out +/-.0002 a couple times. So I seem to be able to measure the bore of the calibration device very accurate, but edge finding sucks for some reason.

The backlash on my machine is a little worse than I would like at .0014 in Y and .0030 in X. I have backlash compensation on and if I go back and forth .015 it will usually land less than +/- .0005 from target or better (my dial indication is .0005 resolution and it usually lands on or within half way of that first mark off zero (so likely +/-.0003 at worst).

Open to ideas? This should at least be better data than I had before to work from.

When I first got this probe up and running, I did have to disassemble and clean all the contacts. The LED was kinda sensitive and flickery (indicating some resistance in the contacts). After I did this, the LED and signal seem fine.

Another thing of note is that if I probe the same thing over and over, the repeatability is always on or within +/-.0001.

I am wondering if I could just manually adjust the radius and XY offsets to dial this in? Is it possible the auto calibration is just not great, or do I have a probe or machine issue?



 
« Last Edit: October 30, 2019, 11:17:04 PM by jevs »

Offline Graham Waterworth

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Re: Probe not matching with edge finder when measuring Y
« Reply #13 on: October 31, 2019, 06:46:29 AM »
You could always have the machine laser aligned and mapped but the backlash is your main issue, to maintain the accuracy you think you need your machine mechanics need to be a power of 10 better, so you are not going to get it.

 
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Offline jevs

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Re: Probe not matching with edge finder when measuring Y
« Reply #14 on: October 31, 2019, 07:53:28 AM »
So you think the backlash is causing the probe accuracy issue with edge finding? Seems odd that it will measure a bore right on and the probe is repeatable, but it cannot edge find decent (compared to an edge finder) and the backlash compensation seems to work as it should.

Offline Graham Waterworth

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Re: Probe not matching with edge finder when measuring Y
« Reply #15 on: October 31, 2019, 09:59:35 AM »
place your setting ring at the farthest most point of the machine in X&Y from the home position, this on most machines is the least used place so is the lease worm part of the screw and slides. calibrate there and then edge find there.

If you find the same errors then its time for a new machine.  End of problem.
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Offline jevs

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Re: Probe not matching with edge finder when measuring Y
« Reply #16 on: October 31, 2019, 11:04:56 AM »
I don't think the backlash is in the screws. I think it is in the end support bearings allowing end play. Long story not related to the probe, but it looks like there is a collar to adjust the slop in the bearings, but it may be all the way in at this point. I am just going to have to tear it apart and see.

New machine is a bit drastic don't you think :)? Other than this, the machine is in excellent condition with little wear and tear. Looks better than most few year old machines in a shop. Do people buy a new machine when it needs a couple bearings or a shim? Even a decent Chinese machine to replace this would probably be $25k. This one was 35k in 1978 when it was new (equates to about $137k in todays dollars). Yeah it is old, but low usage. I had it sitting around tinkering and upgrading it for probably 15 years or something and cut only about 6 parts.....before that it was just used at a college for training. It never was in production. I think I will go the route of fixing the slop instead of buying a new machine. That would kind of defeat the whole purpose of this whole mach conversion.....

Besides this, I am not even sure backlash is causing this. It may be, but It may also be the $100 probe. I don't really know what kind of results people typically get with these things. It just seems odd I can measure a bore to ten thousandths, but not edge find. I am not positive how accurate a Chinese edge finder is either. I found a couple references saying the trip point of an edge finder is pretty tiny, but it is a Chinese edge finder. However, even if the edge finder was off, the difference would be the same at each point and it is not.

 
« Last Edit: October 31, 2019, 11:20:05 AM by jevs »

Offline jevs

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Re: Probe not matching with edge finder when measuring Y
« Reply #17 on: October 31, 2019, 04:28:50 PM »
The more I read about 3D Probes, 3D tasters, and regular edge finders, the more I wonder if my Chinese edge finder is even good or what I should be using as a reference or accurate...
How do I know that is not what is causing the discrepancy I see here. It seems odd I can measure with a known ring gage and the probe measures excellent, but only when I compare to the edge finder measuring edges is there a perceived issue.

Maybe I should be comparing the probe in a different way to make sure the edge finder itself is not the real problem?

It is a bit of money, but those 3D Tasters look nice to have for a mechanical way to check things. Just losing the .1000 math even though it is simple is almost worth it.