# linear encoder



## Karl_T (Jan 11, 2015)

I'd like to try adding a linear encoder to my CNC control. The control needs quadrature differential input at 5 volts.

Anyone know of digital scales that conform to this spec?

So far my only option seems to make my own scale by purchasing a linear encoder kit from US Digital
http://www.usdigital.com/products/encoders/incremental/linear/LIN

Karl


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## JimDawson (Jan 11, 2015)

Renishaw LM10, 1 micron would be my first choice.  Still a few left on ebay.


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## lens42 (Jan 14, 2015)

+1 for the eBay Renishaw LM10s. You'll also have buy magnetic scale tape. I did my lathe DRO this way and it ended up very compact.


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## Karl_T (Jan 14, 2015)

Honestly, my first look at this said,"I still have to build a swarf proof enclosure, might as well stay with USdigital"

Could I see what you did mechanically?

Karl


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## JimDawson (Jan 14, 2015)

Karl_T said:


> Honestly, my first look at this said,"I still have to build a swarf proof enclosure, might as well stay with USdigital"
> 
> Could I see what you did mechanically?
> 
> Karl



I have had these on here for over a year, uncovered, no problems so far.  I just wipe off the strips when needed.  I should make some shields, but I'm lazy.  The solvent for the glue on the mag tape is Xylene, or Acetone.  Not much else seems to affect it.  The Y-axis is continuously soaked in way oil.  Chips don't seem to effect anything.  I think the readers are IP 67 rated.  I am also using these on a 4 axis wood router, they work fine covered in sawdust. 

The full story is here:
http://www.dawsoncontrols.com/millupgrade.html


The X axis








The Y-Axis



The Z- Axis



The K-axis


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## Karl_T (Jan 14, 2015)

Thanks for sharing.

Here I am thinking I need to replicate the enclosures for glass scales. Looks like its not necessary.

Karl


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## lens42 (Jan 15, 2015)

You can either buy tracks for the tape or make them. I milled a 0.4" wide channel in  0.25" x 1" aluminum bar. The mag tape has a self adhesive strip and also comes with a stainless self adhesive cover strip that goes over the top. It seems pretty robust, but I don't use flood coolant.


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## Karl_T (Jan 15, 2015)

SOLD,

You convinced me this is the way to go.


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## chuckorlando (Jan 15, 2015)

Does this work to accurately position the cnc? Acts bout like a dro?


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## lens42 (Jan 15, 2015)

Yes. That is the primary use of the Renishaw read heads. New, they are very expensive. They are really slumming as just DRO heads. 

One warning to Karl T. The EBay Renishaw LM10s have a very short cable. I designed my setup so the heads don't move and send the quadrature signals to a little wireless transmitter under the saddle. If that interests you, search TouchDRO on Google. Of course you could always add more cable by splicing, but the wireless setup is. very slick. 


Sent from my iPhone using Tapatalk


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## JimDawson (Jan 15, 2015)

chuckorlando said:


> Does this work to accurately position the cnc? Acts bout like a dro?



Mine positions consistently to about +/- 0.0001 on the X and Y, and seems to be better than that on the Z.  I'm using the 1 micron (0.000039 inch) readers, 25,400 counts to the inch.  Mine are connected to my motion controller, but many DRO readouts would accept the output from the mag readers.


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## chuckorlando (Jan 15, 2015)

Thanks. I have dros. Just trying to follow along. I really need to learn this stuff. To often a thread just has way to much info in it. This is one aspect so easy to follow. One more piece I suppose.


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## JimDawson (Jan 15, 2015)

chuckorlando said:


> Thanks. I have dros. Just trying to follow along. I really need to learn this stuff. To often a thread just has way to much info in it. This is one aspect so easy to follow. One more piece I suppose.




I looked at my answer to you Chuck, and I didn't really answer your question.

The output from these mag readers is the same as a rotary encoder or most glass scales for a DRO. The DRO readout or motion controller has no idea what it is connected to it just ''sees'' the pulse train from the device.   In the case of a DRO, the software converts that pulse train to a distance and displays that to the user.  A DRO is just a fancy high speed counter.  The standard output from most of these devices is 2 channel quadrature (A, B output) or 4 channel quadrature (A, /A, B, /B), although some (older I think) DROs use a sin/cos output.


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## astjp2 (Feb 18, 2015)

So what display would one need for a mill with z axis summing?  Tim


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## Karl_T (Feb 19, 2015)

The eBay guy that sells LM10 also sells this:
http://www.ebay.com/itm/HB961-count...ut-DRO-meter-meter-counter-NEW-/330824325417?


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