# Unable to calibrate axises



## redvan22 (Mar 20, 2022)

Just got a TouchDRO for my mill and after installation I am unable to calibrate each of the axises.

I followed the instructions from the website using two 1-2-3 blocks, setting the CPI to match the size of the block face (30000 for the 3" face) I was using and I get an odd reading on the DRO and when I input the value into the CPI and test to see if I get the right reading... I get a negative number nowhere near the size of the block face (3.0). I realize that the negative number could be because the direction I'm traveling in but I've tried this on each axis several times and just can't get the calibration right.

As I said I followed the instructions exactly.... https://www.touchdro.com/resources/getting-started/scale-calibration.html
AND watched a video... 




Any help would be greatly appreciated.

Mike.


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## RJSakowski (Mar 20, 2022)

What were the readouts that you got after moving the 3 inches?


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## mchasal (Mar 20, 2022)

redvan22 said:


> Just got a TouchDRO for my mill and after installation I am unable to calibrate each of the axises.
> 
> I followed the instructions from the website using two 1-2-3 blocks, setting the CPI to match the size of the block face (30000 for the 3" face


I think this is your problem, you don't set the CPI to 30000 in step 1 just because you're using a 123 block, you set it to 10000. You only use the size of the block (distance moved) when doing the calculation for the correction in step 3.


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## ycroosh (Mar 21, 2022)

redvan22 said:


> Just got a TouchDRO for my mill and after installation I am unable to calibrate each of the axises.
> 
> I followed the instructions from the website using two 1-2-3 blocks, setting the CPI to match the size of the block face (30000 for the 3" face) I was using and I get an odd reading on the DRO and when I input the value into the CPI and test to see if I get the right reading... I get a negative number nowhere near the size of the block face (3.0). I realize that the negative number could be because the direction I'm traveling in but I've tried this on each axis several times and just can't get the calibration right.
> 
> ...


After the calibration, do you zero-out the axis? I.e. calibrate, move to one edge, zero out the axis, move the other edge and check the reading.


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## redvan22 (Mar 21, 2022)

mchasal said:


> I think this is your problem, you don't set the CPI to 30000 in step 1 just because you're using a 123 block, you set it to 10000. You only use the size of the block (distance moved) when doing the calculation for the correction in step 3.


mchasal,
I setup the 1-2-3- blocks again (long sided)
Zeroed the indicator on the X axis on the first block.
Set the X axis CPI to 10000.
Removed the first block traveled 3" and zeroed the indicator on the fixed block.
The number displayed was -1.5245
I first used this number as a whole (15245) for the CPI and the display read -1.4462
I then divided -1.5245 by 12 and got 1270.4166666 used that number (1270) and the display showed -0.2826
Tried using 12704 and the display read -0.2819

Tried again using 1" travel and the display showed -0.5092 and when I entered that whole number, display showed -0.7284

ycroosch,
According to the video, once the CPI is updated, the correct distance traveled should be shown on the display, 3.0000.

Also, every time I go into Settings, I lose the connection and after making settings changes, I need to wait for the tablet to reconnect. Could this have some bearing on the issue?


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## mchasal (Mar 21, 2022)

redvan22 said:


> mchasal,
> I then divided -1.5245 by 12 and got 1270.4166666 used that number (1270) and the display showed -0.2826
> Tried using 12704 and the display read -0.2819


Why are you dividing by 12? From the instructions: "Divide the reading (ignoring the decimal point) by the *number of inches traveled*." You might want to carefully read through the instructions again.
_ETA: I see now where you got the 12. That was just an example. In your case, it's 3 since that's how far you traveled._

So your CPI math should be 15245/3 = 5081.6...

Try setting the CPI to *5082* and see if that gets you sane results. (You do not ignore the decimal point in this step!)

If you're still having trouble can you take a video of your whole process and share it and maybe we can see what you're doing wrong?


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## redvan22 (Mar 21, 2022)

Ok,
Repeated my steps on the X axis.
123 block clamped down. 
Placed another 123 block next to it long ways and zeroed the DI.
Removed the block and zeroed the DI on the clamped block.
The reading was 1.5240 / 3 = 5080
Entered 5080 for the CPI and the display showed 2.7402


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## redvan22 (Mar 21, 2022)

Please correct me if I'm wrong; the ABS values for all axis should be zero before calibrating?

Now, I re-did the calibration on each axis (after setting the ABS values all to zero and following the instructions carefully) using the 3" side (except for the Y axis where I had to use the 2" side) and what I saw in the video didn't happen for me but after entering the calculated value from the displayed value, I got an unexpected number (at this point in the video, the display showed the actual traveled distance) so I thought, I'll zero out and return to my point of origin and insert the block to see what happens. So I zeroed and then moved the amount of travel until the display showed the correct value (3") and reinserted the removed block and the DI came to zero (actually a few tenths more or less) 

So, does all this sound like I finally calibrated the axis correctly?


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## mchasal (Mar 21, 2022)

redvan22 said:


> Please correct me if I'm wrong; the ABS values for all axis should be zero before calibrating?


Zero or not shouldn't matter. All you're doing is counting the number of steps per inch. Starting from 0 just makes the math a little easier.
See Yuri's correction below.

I'd say if you're getting 3" of travel on the DRO when you move the table 3", you're dialed in.


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## ycroosh (Mar 21, 2022)

mchasal said:


> Zero or not shouldn't matter. All you're doing is counting the number of steps per inch. Starting from 0 just makes the math a little easier.
> 
> I'd say if you're getting 3" of travel on the DRO when you move the table 3", you're dialed in.


Checking the calibration from zero is very important here. This is the most common mistake with calibration.
What happens is that TouchDRO has two offsets that it keeps internally: one from the scale zero to the absolute origin and another from absolute origin to incremental origin. Those are stored in microns. When you calibrate the scales, you change the ratio between scale encoder increments and microns, so the offsets change. This is why is VERY important to check the calibration from 0, as redvan22 did above.


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## redvan22 (Mar 21, 2022)

ycroosh said:


> Checking the calibration from zero is very important here. This is the most common mistake with calibration.
> What happens is that TouchDRO has two offsets that it keeps internally: one from the scale zero to the absolute origin and another from absolute origin to incremental origin. Those are stored in microns. When you calibrate the scales, you change the ratio between scale encoder increments and microns, so the offsets change. This is why is VERY important to check the calibration from 0, as redvan22 did above.


So then I did it right and can now proceed and rely on the DRO?


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## redvan22 (Mar 21, 2022)

So then I'm good to go and can rely on the DRO readings?


apologies for posting this twice. didn't see the previous on a refresh.


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## ycroosh (Mar 21, 2022)

5080 is spot on for 5-micron glass scales, so that number makes sense. I think you should be good to go.


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## redvan22 (Mar 22, 2022)

One last question ycroosch,
How do I calibrate the x and y on a lathe?


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## RJSakowski (Mar 22, 2022)

redvan22 said:


> One last question ycroosch,
> How do I calibrate the x and y on a lathe?


Essentially the same as for the mill. For the z axis, I placed a stop on the lathe ways and brought the carriage to touching and zeroed the axis.  Then I placed a 1/2/3 block between the stop and the carriage and brought the carriage to touching the block .  Alternatively, you can use a dial indicator and zero it against the stop and the 1/2/3 block.

For the x axis, I used my tool post for the stop.  My lathe has flat tops so the 1/2/3 block sits nicely.  For some older lathes with curved surfaces, it becomes more complicated. It could be done on my Atlas/Craftsman 6x18 by replacing the tool post with a 1/2/3 block to act as the stop for the zero and positioning a second block against the stop for the 3" distance.  Basically, you just need a means of fastening a flat surface perpendicular to the direction of travel and supporting a block of known length against it for the change in distance.  It needen't be a block or even a fixed length as long as you can accurately measure the length.  A pin could be turned on the lathe and measured with a micrometer.


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## redvan22 (Mar 23, 2022)

If I dismantle the lathe or mill for cleaning and oiling, do I need to recalibrate?


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## RJSakowski (Mar 23, 2022)

redvan22 said:


> If I dismantle the lathe or mill for cleaning and oiling, do I need to recalibrate?


I would think it wouldn't be necessary .  The only error that could arise would be a cosine error which would be minuscule.  However, it wouldn't hurt to check the calibration from time to time.   It's a fairly simple and quick process.


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## ycroosh (Mar 23, 2022)

redvan22 said:


> If I dismantle the lathe or mill for cleaning and oiling, do I need to recalibrate?


You don't *need* to calibrate. Most low-end DROs don't even have this option and people use them every day. That said, why wouldn't you want to calibrate? You get more accuracy for free. As RJ said, cosine error is pretty minuscule, but the process takes a few minutes once you get the hang of it.
Regards
Yuriy


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## redvan22 (Mar 23, 2022)

Thank you everyone. Been very helpful


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## redvan22 (Mar 29, 2022)

Ycrooch,
After calibration of both the lathe and mill something didnt seem right so on the lathe, I setup for a cut by zeroing out the x axis (x and y same as a mill) and turned a diameter to a random length. Used two vernier calipers to check the length which showed the same value but what the calipers reported was not what the DRO showed so I tweaked the calibration setting number for the x axis until the display matched the calipers. Then I took another cut, measured and again the numbers were off again so I tweaked the setting number again and this became an on going process. Why is this happening? 

When I did the calibration, I did it several times to ensure I got the same results each time but the numbers weren't what you stated earlier, 5080. The x axis was 5074 and the y 5087.


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## mchasal (Mar 29, 2022)

Just to clarify, you're calling the carriage movement the X axis and the cross slide the Y, right? I believe the "standard" is a bit different with the carriage being Z (the spindle anchors the coordinate system) and the cross slide being X: https://www.hobby-machinist.com/threads/x-y-z-on-a-lathe.44499/ 
It seems a bit confusing and I'm not 100% sure , but as long as we're all on the same page; what you're seeing is that the cross slide travel on the DRO isn't matching reality (as defined by your 2 calipers), correct? Can you detail what your calibration process was and also what you're test procedure was for making the cut? 

Are these the same brand/type of scales that you put on the mill?
How are you tweaking the calibration numbers when you try and correct it?
Did you try setting it to 5080 and seeing if the measurements match then? 
Are you getting the same wrong measurement repeatedly or is it varying?

My initial concerns are to ensure you're using the same reference point for all the measurements and to ensure that you don't have some issue with mounting or interference with the scales.


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## redvan22 (Mar 30, 2022)

mchasal said:


> Just to clarify, you're calling the carriage movement the X axis and the cross slide the Y, right? I believe the "standard" is a bit different with the carriage being Z (the spindle anchors the coordinate system) and the cross slide being X: https://www.hobby-machinist.com/threads/x-y-z-on-a-lathe.44499/
> It seems a bit confusing and I'm not 100% sure , but as long as we're all on the same page; what you're seeing is that the cross slide travel on the DRO isn't matching reality (as defined by your 2 calipers), correct? Can you detail what your calibration process was and also what you're test procedure was for making the cut?
> 
> Are these the same brand/type of scales that you put on the mill?
> ...


Mchasal,
I attached a document of every step I took to calibrate and test. (Didn't like the way the Word document was acting so i pasted the text below.)
As for your questions... two different brands of calipers, this time I didn't tweak the calibration numbers, didn't try 5080, several cuts give me off measurements each time.

Setup…
Axis changed for carriage from x to z and the cross slide changed from y to x.
CPI for both axis set to 10,000.

Z axis…
Hard stop setup on ways.
Two 123 blocks placed long end to long end against hard stop.
Incremental and absolute set to zero on z axis.
Removed one 123 block and moved carriage up to remaining 123 block.
DRO reading shows – 1.5256
Divided by 3 = 5085.
Set CPI for z axis to 5085
After reconnection, zeroed z axis.
Replaced 123 block and moved carriage up to it for a snug fit and display showed 3.0002

X axis…
Setup two 123 blocks 1” side to side against back of cross slide micrometer dial.
Moved cross slide up to blocks.
Zeroed x axis.
Removed one 123 block.
Moved cross slide up to remaining block and display showed 5084.
Set CPI for x axis to 5084.
Moved cross slide back until display read 1.0000 and inserted 123 block for a snug fit.

Test…
Chucked a piece of ½” steel stock in vise. 1.5” stick out.
Faced and zeroed z axis.
Took .005 cut ending at .7374 on DRO.
Measured cut distance with digital caliper which read .7390
Measured cut distance with non digital caliper which gave reading of .738

Thank you,
Michael.

UPDATE:

Went back to try new cuts and this is what happened,
First cut DRO showed .5425, DC was .5395 adjusted the CPI until I got as close as I could which was .5391 @ 5102 CPI
Second cut DRO showed .5640, DC was .5675 adjusted the CPI until I got close and that was .5674 @ 5097
Third cut DRO showed .6131, DC was .6185adjusted the CPI until I got close which was .6187 @5089

Please explain.


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## mchasal (Mar 31, 2022)

redvan22 said:


> Mchasal,
> I attached a document of every step I took to calibrate and test.


It looks like you're seeing less than 2 thou of difference between all 3 measurements.

Your calibration procedure looks right as far as I can tell, but the "snug fit" of the carriage against the 123 block could vary enough to explain it. You could try it with a dial indicator to get a more repeatable position. 

Or it might just be the tolerance/rigidity of the lathe. I don't know what machine you have or what condition it's in, but you could get some flex or slop that would explain this.

Or it could be measuring tools. Looking at some random digital calipers, they list their tolerance of +- .0012 so even in that one caliper there's enough tolerance to explain this difference and then there's the tolerance of the scales themselves that stack on top of that.

So I don't think you're doing anything wrong, but it just might be as good as your setup can do. Chasing these last few tenthou's down is probably above my paygrade, but if it were me, I'd turn off that 4th digit(except for calibration) and accept that level of tolerance. Maybe Yuri or some others that are in those paygrades above me can offer some other suggestions.


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## Zertsman (Mar 31, 2022)

some thoughts,

in the absence of pictures of what you are doing...    if the side of the carriage is cast and painted like mine, the 123 block will touch at a different dimension, because of paint thickness, each time as it's not a machined and predictable surface to locate from.  a .002 difference may be spot on.

If you have a bolt head or other small feature that would be a more predictable contact point, use that and you may get better numbers.


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## redvan22 (Mar 31, 2022)

Zertsman said:


> some thoughts,
> 
> in the absence of pictures of what you are doing...    if the side of the carriage is cast and painted like mine, the 123 block will touch at a different dimension, because of paint thickness, each time as it's not a machined and predictable surface to locate from.  a .002 difference may be spot on.
> 
> If you have a bolt head or other small feature that would be a more predictable contact point, use that and you may get better numbers.


I understand and I've milled the saddle to fit a carriage locking mechanism and the 123 block actually touched part of that mechanism so it was a solid touch-off. However, .0002 is nothing in my book to worry about since I'm only a hobbyist and have no military contract orders to fill.


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## redvan22 (Mar 31, 2022)

mchasal said:


> It looks like you're seeing less than 2 thou of difference between all 3 measurements.
> 
> Your calibration procedure looks right as far as I can tell, but the "snug fit" of the carriage against the 123 block could vary enough to explain it. You could try it with a dial indicator to get a more repeatable position.
> 
> ...


I think you missed the overall picture. Every cut requires tweaking the CPI to get it to display an accurate measurement - this should not be happening. It should be calibrated and used with some degree of accuracy repeatedly without the need to adjust the CPI after each cut. What would be the point of having it then?

It's been said by you and Yuiry that 5080 is spot on but look at the CPI numbers I've had to use to get close on my cuts, they're nowhere near 5080. I'll take your advise and eliminate the fourth digit, not necessary for the work I do anyway but I did expect it to be closer than 3-5 thousands.

I have a Micromark lathe and mill. For the lathe, I've lapped and scraped both the cross slide and compound respectively to get as much rigidity out of them as possible. I even added the brass carriage adjustable gibs from a contributor here at this site to the carriage. I can take a .025 cut in steel with no chatter. The machine could probably be a little tighter but its 300% better than it was out of the crate. It doesn't get used every day, I'm a hobbyist, but it gets a regular cleaning and oiling and I've even installed button oilers for quick lubrication of the dovetails.

As for the mill, I lapped every dovetail, including the headstock, until it's smooth and tight. I can take a .020 - .025 cut in mild steel with no chatter. (Headstock locked of course)

My thoughts are that it's the tablet I'm using since I've experienced this strange behavior on both machines using the same tablet for both but I do not know for sure if that could have a bearing on this or, as you said, it could just be the limits of the machine. Someone with more technical knowledge would have to speak up.

Thank you again,
Michael

EDIT:
Had the lathe doc wrong.


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## mchasal (Mar 31, 2022)

redvan22 said:


> I think you missed the overall picture. Every cut requires tweaking the CPI to get it to display an accurate measurement - this should not be happening. It should be calibrated and used with some degree of accuracy repeatedly without the need to adjust the CPI after each cut. What would be the point of having it then?


Sorry, I hadn't seen your updates when I posted that reply. Right, you should not be needing to adjust the CPI between cuts and it would not be very useful if you did. 

Do these variations only happen when you actually cut? Like can you setup the 123 blocks, do the calibration, then keep repeating that same movement and always get 3.000" (or whichever side) over and over? And try different locations in the travel and different sides or other measurements. 

If it does repeat reliably with no force, maybe the stress of cutting is actually causing something to move? Like the scale or the read head isn't quite stable or even the tool or compound slipping?

I don't know if the tablet could cause something like this. I guess it would have to be missing pulses from the scales, or the scales themselves could be flaky. Yuri would be better to elaborate on possibilities there.


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## JFL4066 (Apr 1, 2022)

My 2 cents...
Calipers are not very accurate and repeatable. 

You should buy or borrow a Mitutoyo or Starrett micrometer and depth micrometer *with *the standard. Use those to measure the diameter and length of part. I have personally seen calipers off 1.5 to 2 thou. They really should only be used to get a ball park size when machining up to 5 thou then check with a mic.


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## redvan22 (Apr 1, 2022)

mchasal said:


> Sorry, I hadn't seen your updates when I posted that reply. Right, you should not be needing to adjust the CPI between cuts and it would not be very useful if you did.
> 
> Do these variations only happen when you actually cut? Like can you setup the 123 blocks, do the calibration, then keep repeating that same movement and always get 3.000" (or whichever side) over and over? And try different locations in the travel and different sides or other measurements.
> 
> ...


The instructions that came with the kit said to mount the reader close to the scale but not touching. Only the wipes should be touching the scales. Is there a specific distance required between the reader and scales to get an accurate reading?


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## mchasal (Apr 2, 2022)

redvan22 said:


> The instructions that came with the kit said to mount the reader close to the scale but not touching. Only the wipes should be touching the scales. Is there a specific distance required between the reader and scales to get an accurate reading?


Not sure, but the specs for your scales should provide one if it's important. I don't know if that could cause inaccuracies or just not reading at all though. 

I'd try an isolate it to cutting vs not cutting first to try and narrow down where the issue could be as I posted above.


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## Winegrower (Apr 2, 2022)

I have to say for the record that the plural of axis is axes.   Not axises.


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## JFL4066 (Apr 4, 2022)

My Ditron glass scales spec it around 1mm distance between read head and scale and maintain that distance within a tolerance of +/- 0.002" I believe. 

What's is important is the head is in the same Plane as the scale. ie. it is riding squarely above the scale body. It will eliminate undue wear on the internal assembly. The internal assembly "floats" somewhat to allow for some variation.


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## redvan22 (Apr 5, 2022)

I used a Mitutoyo depth gauge after repeating my cut and it measured what the DRO showed (in a 00.000 format). The caliper was .002 over. SO, I believe I'm in the right neighborhood and will now start my project. I still need to check the Mill and repeat the process to see if things measure up. I believe they will, using the 00.000 format.

Thank you everyone for your time and patience.
Michael.


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## redvan22 (Apr 17, 2022)

UPDATE:
During a cleaning of the lathe, I noticed that the head for the X axis was not parallel but it was perpendicular to the scale along the length. There was about a 1/32' gap at one end and I could just barely get a 0.002 shim in the other end. Maybe I didn't tighten the bolts securely during install, maybe vibration loosened it, don't know for sure. So I realigned it leaving a 0.005 gap between the head and scale along it's length and, during recalibration, discovered that the readout number was exactly 5080. This forced me to check the Z axis and that one too was not aligned correctly. With the Z axis being under the carriage and out of reach, I went with the measurements in the instructions when installing. Well, this was a big mistake. The head was tilted about 2-3 degrees to starboard looking from the tailstock end and was rubbing along the scale on one edge. Once this was corrected (after many trial and error fittings) also got a 5080 reading during recalibration. I was suspicious about the gap between the read head and scale earlier on in this thread and this confirms my suspicions - the head needs to be absolutely parallel and perpendicular to the scale and as close as possible without scraping, as JFL4066 said.  Perhaps 0.005 is not enough or too much but I can't argue with the results. I checked the calibration 3x and got the same number each time - this was another issue before, different readout numbers each time I calibrated. Now there is consistency and I feel confident that I'm in a good place. Very happy that I didn't start my project before discovering these issues.

Again, thank you all very much for your time , knowledge and patience.
Michael.


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## JFL4066 (Apr 17, 2022)

Outstanding troubleshooting. I just installed dro scales on my monarch 10EE.
They were Ditron scales. DC10 and DC10F. It helps enormously if you leave the red spacer/locking piece that holds the read head during shipping in place. It maintains squareness and gap when you are fitting/mounting. Just remove the mounting screws that keep the spacer in place. This allows the head to slide and the spacer maintains the gap.


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