# Cheap DIY DRO scale, do they work?



## Holt (Jan 25, 2014)

Its been a while since my last thread, http://www.homemodelenginemachinist.com/f28/i-stole-lathe-16864/ and this is about the same lathe, I have been wanting DRO from the start, but have run into problems every time, I would of course prefer glass scales, but a 1.3 m glass scale for the main sattle is out of my league, I have seen some DRO sets using cheap Chinese digital calipers, which I think is precise enough for my use, the problem is the longest versions is 600 mm.
I then came across these replacement sensor strips for a Wixey saw.





They come in 800 mm lengths and two can be joined to 1600 mm length and have the exact same pattern as a digital caliper.





(photo from YADRO's home page)
I have read about people mounting these strips, but never heard if they worked satisfactory in the long term, anyone know about that?
If this is the way to go I would probably use them with this setup:

http://www.yuriystoys.com/p/android-dro.html


Holt


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## rodw (Jan 26, 2014)

Before you give up on glass scales, try getting a quote from Ditron on AliExpress. I purchased a 2 axis DRO recently for USD $370 delivered to Australia. (Freignt was $119). Admittedly,  my lathe is only 600mm long but the 1 micron scale was only $67 (you could save $10 by going with 5 micron scales) . They also do a nice slimline scale that is smaller than the others out there which was important for me.


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## Holt (Jan 26, 2014)

The big advantage in some of the DIY sets is you can mix different scales on various axes, the Z axis (main sattle) don't require as precise measuring as the X axis in my opinion for more reasons, the X axis is only counting half the length, and the diameter is always the most critical measurement, the compound slide could do with a digital caliper connected to the DRO.


 Holt


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## ycroosh (Jan 26, 2014)

Holt said:


> Its been a while since my last thread, http://www.homemodelenginemachinist.com/f28/i-stole-lathe-16864/ and this is about the same lathe, I have been wanting DRO from the start, but have run into problems every time, I would of course prefer glass scales, but a 1.3 m glass scale for the main sattle is out of my league, I have seen some DRO sets using cheap Chinese digital calipers, which I think is precise enough for my use, the problem is the longest versions is 600 mm.
> I then came across these replacement sensor strips for a Wixey saw.
> 
> 
> ...



Holt,
I just saw 900mm glass scale on eBay for $108 (free shipping with USA) and one 100mm to 400mm between $88 and $95. I haven't tried that seller, but this is almost cheaper than "AccuRemote" scales.
If that is still out of the budget, I would suggest to get a capacitive scale for the long dimension and short glass scale for the cross slide. On the cross slide the cheap scales will give you +/-0.002" in the best case scenario. In practice it might be as much as +/-0.004" on the diameter. Glass scales will be a factor of magnitude more accurate.

I haven't finished a controller that can mix glass and capacitive scales, but if you end going that route I can send you a custom-compiled version. (I'm stuck at auto-detecting the glass scales, but if I know which axis uses which kind I can pre-set that in the custom firmware).

Hope this makes sense.
Thank you
Yuriy


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## Holt (Jan 26, 2014)

ycroosh said:


> I haven't finished a controller that can mix glass and capacitive scales, but if you end going that route I can send you a custom-compiled version. (I'm stuck at auto-detecting the glass scales, but if I know which axis uses which kind I can pre-set that in the custom firmware).
> 
> Hope this makes sense.
> Thank you
> Yuriy



It makes perfect sense, I have a Heidenhain glass scale for the cross slide, unfortunately it's an old sine wave scale, but I managed to get an interpolation box which put out TTL signals, the down side is I haven't got a clue how I should connect it, the pinout don't make any sense to me.









Now that I got you. I have done lots of electronic, but never programmed such a controller, does your firmware come in a file I can load from my PC?
I have tried searching program loading for dummies, but it seems all guides are written to people with much more knowledge than me.
Thanks.
Holt


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## Holt (Jan 26, 2014)

ycroosh said:


> I'm stuck at auto-detecting the glass scales


 
 Would it be possible to make a program that uses dip switches to set each port manually, it's only the first time you have to set the switches, you don't change the scale type on a regular basis.


 Holt


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## ycroosh (Jan 26, 2014)

Holt said:


> It makes perfect sense, I have a Heidenhain glass scale for the cross slide, unfortunately it's an old sine wave scale, but I managed to get an interpolation box which put out TTL signals, the down side is I haven't got a clue how I should connect it, the pinout don't make any sense to me.
> 
> 
> 
> ...



Holt,
First of all, if you know which pins output the sine wave, you can connect the scales directly to the interface board: http://www.yuriystoys.com/2013/10/voltage-shifter-circuit-for-mixed-scale.html. The comparators will "square" the signal. You might need to replace the voltage dividers that set the virtual ground to potentiometers and tweak the level if the sine waves aren't at the same level.
Take a look at this section of the project page: http://www.yuriystoys.com/p/android-dro.html#msp430_2

With that said, it looks like your scale output "double ended" signal. I.e. each line has a symmetrical complimentary line. This is a superior setup, since it cancels the noise, but if you're not planning to run the wires across your house, you can ignore the negative lines. I suspect that L1 and L2 lines are A and B, L0 is the "R" or "Z" signal (that you can ignore). If you end up using the interpolation box, Connect Ua1 to A input, Ua2 to B input,  Sensor + to +5V (Vcc) and Sensor 0V to the ground.

As far as programming the chip, this should help: http://www.yuriystoys.com/2013/09/how-to-upload-firmware-to-msp430.html

Finally, the problem with DIP switches is that I don't have enough input pins left on that microcontroller. I think what I will do is "assume" that capacitive scales have to send the position in no more than 1 second. If I don't see it, I must be dealing with the glass scales. This means that a user will need to reset the unit when plugging/unplugging the scales but it shouldn't be too big of a deal.

Regards
Yuriy

EDIT: Just found this document on the manufacturer website: http://www.heidenhain.de/de_DE/php/dokumentation-und-information/dokumentation/prospekte/popup/media/media/file/view/file-0429/file.pdf Page 39 has the information you're looking for.


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## Holt (Jan 26, 2014)

Thank you for the links, I have missed that guide, I thought I had red it all, but apparently not.
It seems that there is more to the interpolation box than just converting the sine wave to square wave, it reads the sine wave and put out (in my version EXE 610C) 5 or 10 times the numbers of signals than the numbers of sine waves (being this technical my English starts lagging)









 Also explained here http://www.lna.br/~det/Projetos/TCSPD/doc/HeidenheinEXE602.pdf


 Holt


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## ycroosh (Jan 26, 2014)

Holt said:


> Thank you for the links, I have missed that guide, I thought I had red it all, but apparently not.
> It seems that there is more to the interpolation box than just converting the sine wave to square wave, it reads the sine wave and put out (in my version EXE 610C) 5 or 10 times the numbers of signals than the numbers of sine waves (being this technical my English starts lagging)
> 
> 
> ...



In that case simply connect Ua1 and Ua2 to the A and B inputs on the adapter board, +5 to +5 and 0V to the ground and you're good to go.
Is this the scale you will be using for the cross slide or the longitudinal travel? In any case, the adapter board can do 4 inputs. You need only 2, so you can skip half of it.

Thank you
Yuriy


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## Swifty (Jan 26, 2014)

I've been thinking about a 2 axis readout for my lathe, will probably go the same way that RodW did, and order the lot from China.

Holt, I've only noticed the pic that you use for your avatar, I have the same knurling tool and think that it's great.

Paul.


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## Holt (Jan 27, 2014)

ycroosh said:


> Is this the scale you will be using for the cross slide or the longitudinal travel? In any case, the adapter board can do 4 inputs. You need only 2, so you can skip half of it.
> 
> Thank you
> Yuriy



 Thank you for your patience, I am using the glass scale for the cross slide, the rest should be caliper type scales, I am planning a scale on the compound as well.
 I would love to  take you up on your offer on a custom firmware, by the way, do you know if I can use a tablet without Bluetooth if I use a usb Bluetooth dongle


 Holt


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## ycroosh (Jan 27, 2014)

Holt said:


> Thank you for your patience, I am using the glass scale for the cross slide, the rest should be caliper type scales, I am planning a scale on the compound as well.
> I would love to  take you up on your offer on a custom firmware, by the way, do you know if I can use a tablet without Bluetooth if I use a usb Bluetooth dongle
> 
> 
> Holt



Not likely. I haven't seen a USB dongle that works with a table yet. They might exist, but I haven't seen one ...
Your best bet is to use a FTDI breakout board (in the USA you can get it from Sparkfun.com. Don't know if they ship to Europe) in place of the Bluetooth transceiver.

Regards
Yuriy


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## Walltoddj (Jan 27, 2014)

Swifty said:


> Holt, I've only noticed the pic that you use for your avatar, I have the same knurling tool and think that it's great.
> 
> Paul.



I'm interested in your knurling tool as well are there plans and where can I get them. They had one in Home Shop Machinist but I didn't care for the design.

Todd


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## Walltoddj (Jan 27, 2014)

Holt said:


> Thank you for your patience, I am using the glass scale for the cross slide, the rest should be caliper type scales, I am planning a scale on the compound as well.
> I would love to  take you up on your offer on a custom firmware, by the way, do you know if I can use a tablet without Bluetooth if I use a usb Bluetooth dongle
> 
> 
> Holt



I'm not what tablet you have but my Ipad has Bluetooth in it I've yet to get it to work but it's in there. I have a Kensington  Bluetooth usb plug in for my desk top but just have not been able to get them to talk.

Todd


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## Swifty (Jan 27, 2014)

Walltoddj said:


> I'm interested in your knurling tool as well are there plans and where can I get them. They had one in Home Shop Machinist but I didn't care for the design.
> 
> Todd



The brand of knurling tool is "Quick", I think that they are made in Austria. They work by actually cutting the knurl, this way it doesn't put much pressure on the workpiece. The knurl is set for the work diameter and then brought in in one pass, lots of little bits of swarf are produced. They are ideal for production work on CNC lathes, I kept mine when I finished work, the home hobbiest would find the cost prohibitive.

When they are set up correctly, there is no change to the diameter of the bar being turned.

Paul.


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## Holt (Jan 27, 2014)

As swifty said, the knurling tool is a industrial grade tool too expensive for most hobby machinists, the pic was taken at work where I was turning a part on our Shaublin 125, that was before I got my own lathe.
 I just ordered the TI MSP430 Launchpad that should be here in a few days, and the Bluetooth Transceiver from China, interesting to see how much the Chinese new year will influence on the delivery time.
 Yuriy, do you have schematics and ideally PCB layout for the voltage shifter, or are the stripboard the only option? (backwards engineering looks a bit unmanageable) when I know exactly which scales I am using, I guess it could be made a bit simpler.


 Holt


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## ycroosh (Jan 27, 2014)

Holt said:


> As swifty said, the knurling tool is a industrial grade tool too expensive for most hobby machinists, the pic was taken at work where I was turning a part on our Shaublin 125, that was before I got my own lathe.
> I just ordered the TI MSP430 Launchpad that should be here in a few days, and the Bluetooth Transceiver from China, interesting to see how much the Chinese new year will influence on the delivery time.
> Yuriy, do you have schematics and ideally PCB layout for the voltage shifter, or are the stripboard the only option? (backwards engineering looks a bit unmanageable) when I know exactly which scales I am using, I guess it could be made a bit simpler.
> 
> ...



Holt,
I don't have a PCB layout (yet). Haven't had time to do it yet. More precisely, haven't had time to finish the tachometer and edge probe input, and didn't want to have two different version of the PCB. 
The (partial) schematic is in one of the posts in my original reply. The stripboard simply combines two of those circuits: 2x(comparator, two voltage dividers and four pull up resistors on the outputs).

For 5V scales with the interpolation box you don't need the comparators. Use a voltage divider version shown here: http://www.yuriystoys.com/2014/01/connecting-glass-dro-scales-to.html. 3V scales (Shahe/iGaging DigiMag/AccuRemote) don't need anything between them and the controller, 1.5V scales need the signal to be amplified, so you can either use half of one LM339 comparator or dream something up using either another comparator or op-amp. 

Regards
Yuriy


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## Holt (Jan 28, 2014)

Thank you very much, your help is much appreciated, I will try to draw up something in the near future and post it here.


 Holt


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## rodw (Jan 28, 2014)

Swifty said:


> I've been thinking about a 2 axis readout for my lathe, will probably go the same way that RodW did, and order the lot from China.
> 
> Paul.



I think this is the way to go. You might get a bit more mounting hardware in the kits ex Singapore on eBay, but my cross slide had to be a custom mount as there was not much room. By making your own mounts you probably get a better install. For instance, I machined up a pair of mounting pads for the longitudinal scale with a 1 degree angle on them to compensate for the bed casting shape and did not need to use any grub screws to align the pads.

Ditron included two quite nice cast  brackets for the longitudinal sensor that included tapped holes but I only used one of them. Extra hardware might just end up in the bin anyway.


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## Holt (Jan 29, 2014)

I have been playing with EAGLE, does this seem right, I am a bit in doubt about the supply at the LM339 at pin 1 - 2 - 13 and 14, it have been a couple of years since my last play with EAGLE, so I am a bit rusty.






 Holt


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## MachineTom (Jan 29, 2014)

What kind of resolution do you get from this setup. You need something in the better than .0005" even if you keep the scaling at .001" on the readout. Can you modify the readings to correct errors in the gaging. 

I found nothing in the articles that addressed the accuracy, repeatability or resolution.

Those would be the first questions to answer.


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## ycroosh (Jan 29, 2014)

Holt said:


> I have been playing with EAGLE, does this seem right, I am a bit in doubt about the supply at the LM339 at pin 1 - 2 - 13 and 14, it have been a couple of years since my last play with EAGLE, so I am a bit rusty.
> 
> 
> 
> ...



Holt,
This looks correct. The only little thing: you can skip R7 and R8. You can tie the two virtual grounds to the first comparator.

Thank you
Yuriy


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## ycroosh (Jan 29, 2014)

MachineTom said:


> What kind of resolution do you get from this setup. You need something in the better than .0005" even if you keep the scaling at .001" on the readout. Can you modify the readings to correct errors in the gaging.
> 
> I found nothing in the articles that addressed the accuracy, repeatability or resolution.
> 
> Those would be the first questions to answer.



MachineTom,
Would this work: http://www.yuriystoys.com/2013/12/selecting-scales-for-dro.html

Spoiler alert, though: Chinese capacitive scales aren't going to be better than .0005". On the other hand, I'm SO happy to have an iGaging scale on my lathe, even though I don't trust it for more than +/-0.002" or so. It still saves me a ton of time.

Thank you
Yuriy


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## Holt (Jan 30, 2014)

You mean like this?






Holt


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## ycroosh (Jan 30, 2014)

Holt said:


> You mean like this?
> 
> 
> 
> ...



Exactly.

Do you mind if I post your schematic on my blog? 

EDIT: You probably know this already... Most 1.5V scales have the frame connected to Vcc; most of the other scales have the frames connected to the ground. Unless you isolate the cpacitive scale (and make sure chips can't short it to the lathe's body) you will probably let the "magic smoke" out of something (probably the voltage regulator on the LaunchPad)

Thank you
Yuriy


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## Holt (Jan 30, 2014)

You are most welcome, but I would like to tidy it a bit up before you post it, I will mail you the result in a couple of days.


Holt


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## ycroosh (Jan 30, 2014)

Holt said:


> You are most welcome, but I would like to tidy it a bit up before you post it, I will mail you the result in a couple of days.
> 
> 
> Holt



Sounds good. Thank you.


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## Holt (Mar 1, 2014)

Well, I went for Yuriy's brilliant TouchDRO and I am using a rotary encoder for the main slide, first reason because I have it, and second reason because it is easy to use with the TouchDRO system, I was afraid it wouldn't be possible to implement into a DRO controller, but with this setup you can insert the counts (steps) per inch independently for each axis, and therefore mix whatever you might have or can get cheap. I got the encoder for main slide, a Heidenhain glass scale with interpolation box resulting in 0.5 micron steps! for the cross slide, and then I just got this old tool height measurer 





One of the scales will be mounted on the compound.
Here is a video of my first test setup, the first red PCB is the MSP430 microcontroller, the next is my board (cardboard  ) and then a short look at the Bluetooth sender, the interpolation box and glass scale over the rotary encoder to my 10.1" android tablet.





I will run a length of timing belt at the back of the lathe to run the rotary encoder, I think I will make a new tread in machine modifications once I get it mounted.


Holt


Oops, just forgot the link to yuriy's site with the project:
http://www.yuriystoys.com/p/android-dro.html


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