# Ditron D80 DRO linear compensation...help?



## Winegrower

I recently added a Ditron D80 DRO to the Takisawa lathe.   It's a good featured DRO, a nice display, miniature scales, etc.   I like it, but in checking its accuracy (not a completely trivial task, as far as I can see) it's off about 3 thousandths in 3 inches.   So, trying the linear compensation feature, which does not work anything like what's in the manual, I can compensate it to either 3 thousandths over size or 3 thousandths undersize...can't hit it on the nose.

It feels like there is some quantization in the math that is blocking me...anybody here have this unit and tried the linear compensation?    If so, how did you do?

I have tried both imperial and metric units, same result exactly, just the same equivalent error plus or minus.

Dropros, who I got it from, admits they do not know how this works either.   They've offered an upgrade to another type DRO, but I like the readability of this unit.   I hope I can keep it.

Dang it.


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## mksj

I believe the problem may be the resolution of the scale, and if this is on the cross slide in diameter mode.  A 5 micron scale will increment in jumps of 0.0004" in diameter mode and this limits the steps depending on the linear compensation increment of how it is applied, so the error adjustment if off is multiplied by the linear compensation increments. So I would expect that the correction applied is limited by the scale resolution setting. The long axis would increment in 0.0002" with a 5 micron scale. A few things you may try, it may have something to do with the measured length and how the error calculation is performed/applied, so maybe see what happens if you apply the error compensation over the full length of travel vs. say 1" if that makes any difference, but I still believe you may have an issue with how the correction is applied for the scale resolution.

FYI I had a 5 micron scale on my cross slide and had similar issues with rounding and calculation errors when entering values on my Easson ES-12B, these went away when I switched to a 1 micron scale on the cross slide scale.


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## Winegrower

Humm...you could be right here, mksj.   An excellent thought.   I’ll try the longer travel distance for calibration.
I don’t believe there is a 1 micron scale in the mini size, though the D80 can be set to that resolution.


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## Winegrower

Just for the record, mksj has made some valuable private message comments, facts and suggestions, and I am in pursuit of resolution with the manufacturers and vendors.

Thanks, mksj!


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## peter.van.haren

Following. 
Just ordered a Ditron D80 and DMS 1um magnetic scales from Ditron direct the other day. Excellent sales service. Not sure about after sales yet though.
Have you asked them? Abigail was her name at sales7@dcoee.com. 
Excited to try my DRO.

Sent from my SM-N960F using Tapatalk


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## bill70j

Winegrower said:


> I like it, but in checking its accuracy (not a completely trivial task, as far as I can see) it's off about 3 thousandths in 3 inches.



Are you using gage blocks and a DTI to check physical movement vs the DRO readings?  I ask because I tried a couple of other approaches and never got real good readings.  Finally, using gage blocks, the readings came within 0.0005" of each other over 4" of travel.

I also made the mistake of trying to get the DRO to line up with dial readings.  Big mistake there too.

My DRO is not the same as yours, but does have the linear and non-linear compensation functions.  My manual specifies calculating a factor which is essentially the percentage difference between the readings, and entering that value along with the appropriate + or - sign.

Curious to hear what you find out!


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## pontiac428

I have a D80 new in box sitting on my mill that's not going to get installed right away.  I'm definitely interested in how it works out for you!


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## Winegrower

I have been slow to get back on this problem, but here's where I am:

1) Todd at DRO has been as helpful as could be, but has not seen the problem I describe.   He has sent a replacement scale to try...have not done that yet pending some new insight that I need.

2) I have gone over about 4" of X-axis travel measuring against the lathe dial indication, the DRO reading, and a 0.0001" dial indicator, resetting it at the end of its travel, about 0.050" as I recall.   Might be 0.01".

3) I find that things look normal most of the time, and over long distances the DRO reading correlates with actual travel very well.   However over certain even short distances, as short as 0.030", there can be an error of about 0.003".   I tried very hard to capture a record of this, logging all the data.   Do you know how many 0.0001's there are in 4 inches?        I got to where I had narrowed down the error, thought I had it all captured, and decided to blow any chips off the scale.   Huh, problem changed, would not repeat.   Without redoing the entire experiment, the particular error I was after went away, but the issue still exists in places, random places.

4) I am thinking that this is not a linear or non-linear compensation problem, as the DRO reads correctly over long distances, and I also don't think this is a scale resolution issue, though it's clear that a one micron scale would be superior.  

5) I don't think there's any basic issue with the D80 DRO.   I like it, it's easy to use (except compensation) and easy to read.

6) So I am suspicious about the ability of the magnetic scales to resist small ferrous chip contamination, mainly based on the change when I blew off the scale.  

  I am attaching two pictures, in hopes that someone here will suggest something great:

7) The first picture is the scale and reader installed on the tailstock of the carriage, which is attractive with these smaller scales as you don't lose much tailstock quill travel.   I installed the scales "vertically", I would call it.   You can see that it somewhat exposes the scale to chip collection, I suppose.

8) The next picture is of the scale with a magnetic "developer" held against it.   This just shows the large scale magnetic patterns.   There are two tracks, one at short spacing and one at much larger distance between transitions or zones.   The reader has a green light that shows red when it's over the larger distance zone, by the way.

I know this is hard to read, and I apologize.  It is simply reflective of how confused I actually am.   I hope that someone here might really truly understand and be able to explain what is actually recorded on the scale, how the reader interprets that, and if it is possible that ferrous material could give a transient error.   The error always seems to show a smaller than actual distance, by the way.

If contamination by magnetic material is the issue, then I could see some possible solutions:
1) Relocate the scale elsewhere.
2) Cover the scale better.
3) Give up and go to glass.

The difficulty with just relocation is that it seems like eventually there will be some collection of particles, so maybe not really a solution.

Anyway, I solicit your thoughts and opinions.  Thanks.


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## bill70j

I think your installation looks fine.  It would be ideal to have a cover, but I suppose that would mean having to lower the whole installation so you could affix an aluminum angle to the table or to the scale mount. 

I wonder if you might be losing accuracy and repeatability by trying to measure the x-axis travel using a dial indicator.  I have always thought that DI's and DTI's are great for measuring relative distances, but not so much absolutes.  Plus you may be introducing some error by repositioning the indicator every time it reaches its end of travel.  

Also, your dials may not be a very good measure of travel either.  Wear in the screws and nuts can skew the readings.

You might try measuring travel by using a 4" gage block and a DTI.  Here is one way to do it:

Clamp a 123 block square to the table and zero a 0.0005"DTI -- on a mag base affixed to the bed ways -- against the 123 block.
Zero the DRO and zero the dial
Move the table a little over 4" and position a 4" gage block against the 123 block
Then, without moving the DTI, move the table to re-zero the DTI against the gage block.
Observe the DRO reading and read the dial
I would be a bit surprised if the DRO reading isn't 4.000 +/- 0.0005 and the dial is off by at least 0.001" 
This method assures that you are measuring against a standard 4".

Just a thought.


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## Winegrower

Bill70j, thank you for that.   I agree with your points, and indeed I considered a cover as you suggested, but it would have to go over the reader, and so add to interference with the tailstock.  Your method is good, and is more or less similar to some tests I did where I concluded, as you say, that over a long distance, the DRO reads correctly.   I previously tested all my dial indicators, digital and analog, and basically found they were all plus or minus 0.001", so you're right on.   The dial on the Takisawa is pretty good, but yep, 0.001 would be pushing it.   

My question is, is there a failure mechanism with magnetic scales that debris can cause temporary and localized errors?   That is the closest summary of my problem that I can give at this point.


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## Winegrower

Updating my experience per above, I found these issues with the D80 DRO:

1) DROpros replaced the magnetic X axis strip, not clear if that changed much, but it was a clean platform to restart with.

2) Finally, it became clear that the DRO needed a 0.001” per inch linear compensation.   Trouble was, the manual looked nice but was wrong, or at least incomplete and essentially not understandable.   Eventually I taught myself how to compensate the scale, and the accuracy is good now.  

3) there seemed to be some problems with tiny ferrous chips along the edge of the scale.   This is speculation on my part, based on changing readings as I blew chips away from the scale.   I could be wrong.

4) relating to that, the mag strip is adhered to a frame with a slightly smaller stainless steel cover.   There is a tiny gap where chips could work in between the strip and cover.   I filled the gap with a very small amount of clear caulk.   Will it help?   Too soon to tell, too late to back out.

I am still disappointed with error magnitude when in “diameter” mode.   It seems like larger errors than the 0.0002 resolution of the x axis scale would imply.   Still pondering this.

It’s been an adventure!


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## Winegrower

mksj said:


> FYI I had a 5 micron scale on my cross slide and had similar issues with rounding and calculation errors when entering values on my Easson ES-12B, these went away when I switched to a 1 micron scale on the cross slide scale.



I spent a lot of time trying to understand error sources on my Takisawa lathe and D80 DRO, and how to read and understand the manual.  I never achieved that completely, just enough to do a linear compensation.   I finally decided mksj was correct that a 1 micron X axis resolution was needed to have satisfactory performance in Diameter mode, which doubles the error.   

DROpros were very helpful in that 1) they warned me that this would happen, but only 5 micron was available at the time, 2) they swapped my 5 micron out when the 1 micron was available, and 3) they listened to me fumble through several issues before arriving at an acceptable answer.   I’m happy I didn’t buy direct from China, I would have been even more confused.


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## A watkins

Sorry for the old thread resurrection, but this thread touches on a problem I have with the Ditron DRO. and I haven't seen it discussed anywhere:  I can't make any sense out of how the linear compensation feature works, and it is not documented in the manual.

Once you have zeroed your DTI against one edge of the gage block and then zeroed again at the other end, you have on the DRO what it thinks is the gage block length.  At that point you go to the compensation feature and find three fields, L1, L and S.  L1 is the displayed figure for the length of the gage block you just measured and is not editable.  L is the actual length of the gage block and editable.  S is the "correction coefficient" which according to their description of the arithmetic involved is the error expressed as a unitless ratio. 

The odd thing is the DRO allows you to edit both L1 and S, which I don't get.  I expected simply to edit to tell it the actual gage block size and for it to take the correction from there.  However, when I enter L1 (typically 4.0000") it modifies what I enter somewhat, and then supplies yet another figure for S, neither of which make any sense to me, in part because the L1-L and S differentials don't add up to the error.  So between the auto-modifying L and magically computed S, I have no idea what it wants.

Can someone who's figured this out clue me in?

Thanks,
Alan


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## Winegrower

Alan, I agree that the compensation procedure is described absurdly.   What finally worked for me is that everything must be in metric.   Be sure to do that, then I think everything will begin to make sense.


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## ddickey

I just got done monkeying around with mine for hours. My readings were always inconsistent. Ended up going to back to no compensation for all the slides. May revisit at a later time.


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## RJSakowski

I have a different system so this may not apply.  I found that the compensation entered is applied to the last compensation factor used.  So if you are reading 2.997" over 3" and apply a correction factor (mine is in ppm) of 1000 ppm, the scale should be right on.  If for some reason, it was now 3.001" over 3", I would have over-corrected and need to apply a new factor of - .001/3 x 1,000,000 or -333.  If the new measurement was 3.0002", the last correction wouldn't be enough and the new factor would be -.0002/3 x 1,000,000 or -67.  Continue until you are satisfied with the calibration or bored whichever comes first.

If using a 1-2-3 block for the step, I would measure the block with an accurate micrometer.  Use that measurement rather than the nominal size.


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## RJSakowski

A little prep work will help with consistency of measurement.  On the mill, I clamped a 6" bar parallel to the axis being calibrated and swept the edge to verify.  Then I clamped a1-2-3 block at one end for a stop.  For my step, I used a 6" parallel measured with a micrometer.  The test indicator was mounted in the spindle and the spindle fixed so it couldn't rotate.  I now had a stable repeatable system.  I zeroed the test indicator on the stop block and zeroed the DRO.  Then I moved the table 6+ inches, inserted the parallel, and moved in until the test indicator zeroed.

A similar setup was used for the lathe.


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## Winegrower

I say again, put the DRO in metric, convert your 3” block to mm, and do it just as it says in the manual, which is actually better than most import manuals.   It will work.


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## A watkins

Winegrower said:


> do it just as it says in the manual, which is actually better than most import manuals.   It will work.


Before you send me back to the manual, let me remind of what the manual says:
_---------------------------------------------
2.9 Linear compensation
Function: Linear error compensation function is used to correct the system errors of the grating 
ruler measurement system linearly.

Note: the calculation formula of correction coefficient is:

Correction coefficient S =   ( L - L1)  /  C L / 1000)  mm/m L: Stands for the actual measured 
length (mm)
L1: Stands for the displayed value (mm) on the DRO
S: Stands  for  correction  coefficient (mm/m)  (+ indicating lengthening and - indicating 
shortening)
Compensation range: - 1.9 mm/m to + 1.9 mm/m

Example: The  actual  length  of   the  machine's X  axis  table  is  1000.000mm   and  the 
displayed   value   on  the   DRO is  999.880mm.  The  correction  coefficient is calculated as 
follows:
S =  C 1000.000 - 999.880)  /  C 1000.000 / 1000.000 )  = 0.120
Set the linear compensation  coefficient  according  to the following operation (Note: Set the  
compensation  method  as  linear  compensation  in  the system  parameter setting  section  
firstly.  The  detailed  operations are described in system parameter setting section.)


2. Basic functions

Step 1:Entering the linear compensation Press C to enter the linear
compensation.   Select the X axes by pressing   (left/right arrow)  .After selecting well, press  Enter to enter the 
linear compensation.

Note:  When any axes need to be done the linear compensation.  The corresponding compensation way in 
system parameter setting need to set as the linear compensation(linear)._
----------------------------------------------------------------

Note that it says absolutely nothing about two boxes L and S that are editable on the subsequent screen.

So, Winegrower,  when you had your displayed length of X mm, and your known length of Y mm, what did you enter into L and S?  Did you literally do their computation S from L and L1, and then enter the result along with L?  If so, do you understand why they (apparently) require us to enter L and calculate S when the latter is derived from the former by simple arithmetic?


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## A watkins

A watkins said:


> So, Winegrower,  when you had your displayed length of X mm, and your known length of Y mm, what did you enter into L and S?  Did you literally do their computation S from L and L1, and then enter the result along with L?  If so, do you understand why they (apparently) require us to enter L and calculate S when the latter is derived from the former by simple arithmetic?


The person from Ditron who told me I was to do the calculation and enter both L and S has recanted her testimony and now says:
—————
_1. Clearance Zero under ABS model
2.Press button C ,then enter compensation model
3.ensure a start position,clearance zero,then move linear scale to another position
4.you will see a date (she means “number”) in L1 ,then input a actual measuring length at L, DRO will calculate S
Please note: L means the length between the start position and the end position 
—————-_

So, has the above worked correctly for you other Ditron users? If not, how are you making linear compensation work?


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## Winegrower

I only entered 3” in mm actual, whatever that is.   It figures out one of the parameters, what it thinks the move is, and figures S.   I recall having to follow EXACTLY the sequence the manual describes, even though it seems to be more free form.   Later, I verified S computation with the formula, it checked.


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## A watkins

Winegrower said:


> I only entered 3” in mm actual, whatever that is.   It figures out one of the parameters, what it thinks the move is, and figures S.   I recall having to follow EXACTLY the sequence the manual describes, even though it seems to be more free form.   Later, I verified S computation with the formula, it checked.


I posted the entire text of the manual on this subject; I don't understand what sequence you are referring to.  Could you point it out?


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## Winegrower

A watkins, my shop is covered up for a few days for reroofing.   Honestly, you have it there, these are the steps I went through, lots of trouble until I set the DRO to metric.   It just worked after that.   You only have to enter the your standard’s length...in mm.  The rest is automatic.


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## Winegrower

Ok, here is what works for me:

Press C to enter linear compensation.  Select Axis with arrows.  Move lathe per the reference block.   Select the “L” field, enter the reference distance in mm.   Press Enter.   Then exit by pressing C again.


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## A watkins

Right, and the last part is _*not mentioned in the manual at all*_*,* including that there is an S field that you can also enter or edit.   So insisting that all I have to do is follow the sequence in the manual is nonsense and is why I posted the manual in the first place.  I love going in circles.  And no, that manual is NOT any better thany any other garbage Chinese-product manual.  

Where this all goes south is if you turn right around and run the calibration again.  Imagine that you realized something moved during the first time attempt.  So you enter a new L.  The DRO’s reaction is to refuse to accept what you entered, and instead displays some other number different from the actual length.  In addition it changes S a little.  I have not figured out what it is trying to do, but I have figured out that if you want to redo a calibration from the start, you first have to go in and set S to zero.   Somehow that convinces it to accept your gage block’s actual length.

And by the way, it makes absolutely no difference whether you enter the lengths in metric or inches.  If you look at the formula for S for a second or two you’ll see why.  S is simply the percentage difference between L and L1 (with the decimal point shifted) and as such is unitless.

What about other DROs with linear compensation?  Do they allow you to edit the compensation figure itself?


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## Winegrower

I struggled to calibrate my Ditron system too, but got it eventually, doing just as I said.   Bummer you're having trouble.

You do not have to calculate S.  You only input the actual length, but in mm.   You are correct, it’s a dimensionless number, but you don’t know how the software computes internally.   Note the manual shows the range acceptable only in mm/m.


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## maticulus

Winegrower said:


> I struggled to calibrate my Ditron system too, but got it eventually, doing just as I said.   Bummer you're having trouble.
> 
> You do not have to calculate S.  You only input the actual length, but in mm.   You are correct, it’s a dimensionless number, but you don’t know how the software computes internally.   Note the manual shows the range acceptable only in mm/m.



I purchased this Ditron 5 axis DRO for the PM728 mill for $161 and the price immediately went up on the website by $100 afterwards. I suppose the marketing strategy is to get one person to buy and mention it  before going to the intended price point. I found this thread while looking for more info on the DRO;









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  I mounted a Harbor Freight digital caliper in a vise to check accuracy against the DRO and found the "Y" axis was off by +.0015. I tried to correct it using my understanding of the instructions and two value entries (L & S I believe) unsuccessfully and noted that "S" changed with just one value entry. After doing what you described, entering one value, the error corrected to within a few .000X as far as I can tell since the HF caliper only reads down to 5um increments, vs the 1um scales I'm using. The thousandths position is uniform and the overall measure probably more accurate than I suspect given the temperamental HF caliper.

   The DRO works great so far as I can tell and is a lot more user friendly than the first DRO I purchased, which was returned under the impression of being defective as only two of the four visible axis would read correctly using the same scales. It turns out after the ease of adjusting the settings in the D80 I have now, that the problem may have been a combination of awful instructions which gave no info on how to get into setup, and no info on the password code it appeared to want. nothing I tried from existing procedures on the net worked and an ebay seller that had no clue as to how to get into setup and make crucial foundational changes didn't help either.

   It was a great looking piece of equipment, but without the ability to access all of the parameters a bad deal. This is a heads up for others who might be drawn into it. SDS5-4VA.









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## ddickey

Do you have any jo blocks or even 1-2-3 blocks? Using a caliper is not the way to check a scales accuracy.


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## JimDawson

Winegrower said:


> My question is, is there a failure mechanism with magnetic scales that debris can cause temporary and localized errors? That is the closest summary of my problem that I can give at this point.



I have noted that by pressing with a finger on the magnetic strip a few inches away from the read head will show a change in the DRO reading.  Putting some wipers on either side of the read head might be helpful, but I have not seen a problem on my mill with the strip exposed to everything.


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## maticulus

ddickey said:


> Do you have any jo blocks or even 1-2-3 blocks? Using a caliper is not the way to check a scales accuracy.



  I do have the elementary blocks and will check calibration formally using the absolute method of measure. It actually escaped my mind that the comparison between the DRO and caliper is relative and both need to be checked against a calibrated length for individual accuracy.


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## Ken226

Is this just an issue with magnetic scales?   Are any of you with this issue using glass scales?

     I have Ditron D80 displays from DRO Pros, on both my mill and lathe, but am using them with glass scales.


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## maticulus

Ken226 said:


> Is this just an issue with magnetic scales?   Are any of you with this issue using glass scales?
> 
> I have Ditron D80 displays from DRO Pros, on both my mill and lathe, but am using them with glass scales.



I'm using 1um glass scales and found it necessary to make an adjustment to the "Y" axis. The "X" axis was fine from the start. As mentioned earlier I have to recheck the accuracy against the blocks.


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## Winegrower

My issues were only with magnetic scales, did not try glass.   And for completeness, they were the smaller magnetic scales, don't recall the trade name.


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## pontiac428

JimDawson said:


> I have noted that by pressing with a finger on the magnetic strip a few inches away from the read head will show a change in the DRO reading.  Putting some wipers on either side of the read head might be helpful, but I have not seen a problem on my mill with the strip exposed to everything.


There is a backing strip, the encoder strip, and the stainless guard strip that are all supposed to be adhered together in the scale, but as @JimDawson pointed out, they can be forced to moving.  I don't _think_ they move under operation (air gap between reader and encoder), but I haven't _verified_ that they don't move.  I'm having second thoughts, so I will have to come up with some sort of test to see what I get.  The problem is that once I get over 1", where I have gauge blocks good to .0001", I drop to .001" resolution up to 12" (using calipers or a depth gauge).  That's a configuration that would be blind to step losses at 4um, the resolution of the scale.  Hmmm.  I suppose I have to define an acceptable cal range.  Perhaps .001" in 4" would work for most real-world tasks.


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## Ken226

maticulus said:


> I'm using 1um glass scales and found it necessary to make an adjustment to the "Y" axis. The "X" axis was fine from the start. As mentioned earlier I have to recheck the accuracy against the blocks.




I went out and checked by touching off a 1-2-3 block with my edge finder.   Across the 1" side, on the Y axis it was perfect.  Showed 1.2000", with a .2 diameter edge finder tip.

Across the 3" side on the X axis It showed 3.1998".    So,  .0002" of error.

I did it several times with exactly the same results.  That's with 5 micron scales.  

I'll recheck occasionally, and consider myself fortunate.


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## ddickey

Use a tenths indicator, much more accurate.
Here's a video that shows the way to test scales.


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## Ken226

ddickey said:


> Use a tenths indicator, much more accurate.
> Here's a video that shows the way to test scales.



I went out and set up a a DTI this morning and rechecked.

Using that method,  my X axis shows .0004"  and Y shows .0002".  I suppose I should actually go measure the actual length of the Shars 1-2-3 blocks before I assume anything about scale error.










Edited to add:   both my 1-2-3 blocks mic'd @ 3.0002" long on the 3 inch side.


find the gas station closest to me


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## platypus

Following.


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## Winegrower

Ultimately I stuck a strip of electrical tape over the side of the scales…not the surface the reader moves along.   I think this keeps tiny ferrous particles away from the magnetic strip where they can slightly distort the field.   It helped a lot, to the point I don’t worry about it anymore.


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