[How do I?] DRO troubleshooting

[ARC-170]

I've got iGaging DRO's on all 3 axes of my Rong-Fu mill. The Z axis has constantly given me issues. I finally needed to fix it for a project. I cannot get any consistent readings at all. I set up a DTI to read the Z-axis travel. Here's a picture for your viewing pleasure:

The DTI is from LMS and appears to work fine.

Here's a chart I made after using a DTI as the "standard":

The mill dial and the DRO are not really consistent at all. I did 2 trails with the mill dial, so there's 2 columns for that.

I made sure the fasteners on the DRO were all snug, the z-axis was loose (so it didn't drag or jump), the DTI was fixed.

What is going on? Anyone got any ideas? Thanks!

 

[ChazzC]

Photos of the scale mounts & details would be helpful.

Which version of iGaging scales? Aluminum or SS? Running on batteries or an AC adapter?

 

[markba633csi]

First thing I see is your dti placement/mount looks like it could be improved
AFAIK the mill dial on those is pretty crude so I would disavow those readings
If the problem isn't with the dro electronics then it must be solely mechanical
You really need another dti mounted on the head to compare readings- or move your dti to the head and see if it improves
Worst case you could remove the dro scale, put it on the bench and temporarily mount the dti to it- see if they track exactly as they should

 

[rwdenney]

My favorite way to measure movement for a DRO is using either micrometer standards, gauge blocks, or both. I have micrometer standards to 9" and gauge blocks to 4". I used a 4" gauge block to measure the Z-axis DRO (from Shars) that I installed on my Bridgeport. It's 0.0015" off per inch, which is not good but at least it's consistent. I positioned the knee so that the bottom of a gauge pin chucked up into my spindle was about 4.5" above the vise jaw. I stood a 4" gauge block on the vise jaw, and brought the quill down to the top of the block until the chucke-up gauge pin touched (no force, just touching) the top of the block. I zeroed the DRO and then removed the gauge block and brought the quill down to touch the top of the mill vise jaw. It should read -4.000, but it really read -3.994. That is more accurate than using a dial indicator. Dial indicator tolerances aren't that precise--Mitutoyo, for example, specifies 0.002" per inch.

If you don't have gauge blocks, any semi-decent 1-2-3 block is probably accurate enough for hobbyist use, and still more accurate than a dial indicator for this application. Those are usually within a few tenths, even the cheapies (in my experience).

Rick "how I do it" Denney

 

[ARC-170]

Photos of the scale mounts & details would be helpful.

Which version of iGaging scales? Aluminum or SS? Running on batteries or an AC adapter?

Hope this helps:


I have iGaging EZ-View DRO plus on aluminum rails running off of battery power. I used to have them plugged in, but they didn't seem to work well, so I went back to battery power. I'm not sure that was the cause of my current issue, though (I could be wrong). The Z-axis rail is mounted on the front.

First thing I see is your dti placement/mount looks like it could be improved
AFAIK the mill dial on those is pretty crude so I would disavow those readings
If the problem isn't with the dro electronics then it must be solely mechanical
You really need another dti mounted on the head to compare readings- or move your dti to the head and see if it improves
Worst case you could remove the dro scale, put it on the bench and temporarily mount the dti to it- see if they track exactly as they should

I agree! Ha! It was good enough for what I was trying to do.
The mill dials work okay, but I have quite a bit of backlash: about 0.014" (hence the DRO's).
I think it's mechanical as well. I'll need to fiddle with it and see. I suspect there are several issues that all contribute: loose screws, play, loose mounts, etc.

The DTI is accurate. I used it to set the depth of cuts, made the cut, then measured with 2 different calipers and they all had the same measurement.

I thought it might be the DRO getting interference from the motor electromagnetics or the plug I was using to power it, but then the X and Y DRO's would also be off and they seem fine. I changed the batteries as well.

 

[ARC-170]

My favorite way to measure movement for a DRO is using either micrometer standards, gauge blocks, or both. I have micrometer standards to 9" and gauge blocks to 4". I used a 4" gauge block to measure the Z-axis DRO (from Shars) that I installed on my Bridgeport. It's 0.0015" off per inch, which is not good but at least it's consistent. I positioned the knee so that the bottom of a gauge pin chucked up into my spindle was about 4.5" above the vise jaw. I stood a 4" gauge block on the vise jaw, and brought the quill down to the top of the block until the chucke-up gauge pin touched (no force, just touching) the top of the block. I zeroed the DRO and then removed the gauge block and brought the quill down to touch the top of the mill vise jaw. It should read -4.000, but it really read -3.994. That is more accurate than using a dial indicator. Dial indicator tolerances aren't that precise--Mitutoyo, for example, specifies 0.002" per inch.

If you don't have gauge blocks, any semi-decent 1-2-3 block is probably accurate enough for hobbyist use, and still more accurate than a dial indicator for this application. Those are usually within a few tenths, even the cheapies (in my experience).

Rick "how I do it" Denney

Thanks, I'm going to try this when I get some time this weekend and then I'll report back.

I might also bench-test this and see if the DRO is reading what it should.

 

[ChazzC]

Hope this helps:
View attachment 510421

I have iGaging EZ-View DRO plus on aluminum rails running off of battery power. I used to have them plugged in, but they didn't seem to work well, so I went back to battery power. I'm not sure that was the cause of my current issue, though (I could be wrong). The Z-axis rail is mounted on the front.

Sorry, I wasn’t clear: I meant photos of the scale mount itself, not the readouts, so I suggest how they are mounted may contribute to your isses.

The EZ-View scales are the older version that has Aluminum scales; iGaging Absolute Plus scales are SS and less prone to flexing (which can create issues).

This page on TouchDRO discusses a number of issues with EZ-View scales/readouts:

Common Problems with iGaging EZ-View Scales

 

[markba633csi]

If the motor is off when you are doing the testing then it must be a mechanical issue- not electrical

 

[ChazzC]

If the motor is off when you are doing the testing then it must be a mechanical issue- not electrical

Can still be a grounding issue

 

[markba633csi]

No, he's on batteries- I don't see how grounding would matter
Possible I suppose but I'm doubtful.
More doubtful than the usual amount- doubtful 2.0