# DRO linear glass scale adaptation.



## mikemm (Nov 29, 2018)

Hi all,

I have a 9 x 42 Bridgeport with a Mitutoyo DRO with 750 mm glass scale on x axis. Machine has plenty of use with moderate wear in the ways and screws.

I just came across a 9 x 32 Bridgeport  with non chrome ways with all the original flaking clearly visible everywhere with almost no wear at all anywhere on machine with a super quiet head.  I practically stole this machine for $300.00. Guy just wanted it gone and I couldn't resist. He even threw in a granite surface plate and a 12 inch Kamakura rotary table.

The shorter table actually works better for my space as I never have long parts to work on. I would like to move my DRO onto this machine. The y axis is not a problem but the x axis scale is longer than the table and I am not sure how to attach and what type of bracket to fabricate and if its even possible.

I would love to hear some suggestions.

Thanks


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## JimDawson (Nov 29, 2018)

I guess I would bolt a piece of 1/2 x 2 aluminum bar stock to the table, then mount the scale to that.  I also understand that it's possible to cut the scale, but I have never done one.

Sounds like you bought a rotary table, and they threw in a BP and surface plate.


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## Janderso (Nov 29, 2018)

I don't see any pics, what do they say if there are no pics? It didn't happen??
Share man,  share.


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## Dynahoe Dave (Nov 29, 2018)

I cut a scale for mine.   Go slow and use care.  I can add details later.


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## mikemm (Nov 29, 2018)

If I use bar stock, I guess I will need to mill some relief slots in the stock where it will block the table drain holes. I also like the idea of cutting the scale. I don't know how practical that is though. Assuming I open the scale and see that milling away 10 inches of the housing still leaves enough supports for the glass element, there is also the mystery of cutting through the glass without ruining it. would love to hear how its done.


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## RJSakowski (Nov 29, 2018)

DRO Pros sells individual scales at a reasonable price.  I would consider just getting another scale.  If you decide to use the longetr scale with a bar, you can mount the bar on standoffs to clear your drain holes.

BTW, you got a super deal!


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## JimDawson (Nov 29, 2018)

mikemm said:


> If I use bar stock, I guess I will need to mill some relief slots in the stock where it will block the table drain holes. I also like the idea of cutting the scale. I don't know how practical that is though. Assuming I open the scale and see that milling away 10 inches of the housing still leaves enough supports for the glass element, there is also the mystery of cutting through the glass without ruining it. would love to hear how its done.



Normally the drain holes are in the back, I always mount my scales on the front so I don't lose Y travel.


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## Jubil (Nov 29, 2018)

Why can't I ever find a deal like that? I'm not jealous, I'm mad. Lol. 
Congratulations on the find.
Chuck


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## Holescreek (Nov 29, 2018)

Just cut the scale down to the proper length and mount it like it was on the old machine.


https://www.hobby-machinist.com/threads/new-import-cheap-dro-for-the-traytop.50579/


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## mikemm (Nov 29, 2018)

JimDawson said:


> Normally the drain holes are in the back, I always mount my scales on the front so I don't lose Y travel.


.
The servo limit switch is in front leaving the back of table as only option for scale. 



Jubil said:


> Why can't I ever find a deal like that? I'm not jealous, I'm mad. Lol.
> Congratulations on the find.
> Chuck



Thanks, I keep pinching myself on this find. So many kept slipping through my fingers in the 2k + range which I though were great deals at the time as the local rebuilder wanted 4K to scrape all 3 axis on my machine. I took a total chance figuring I was wasting my time to go see it. Its a 1968 machine with step pulley head but who cares at this price. The paint is all checked from being stored in an unheated space and the table needs a molasses bath for the next month or so to bring it back but otherwise its practically new.

I think im going to try to resize the scale


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## JimDawson (Nov 29, 2018)

mikemm said:


> The servo limit switch is in front leaving the back of table as only option for scale.



I always just removed the limit switch, never could see a good use for it.  I have seen scales spaced out a bit so they clear the switch and stops.


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## Dynahoe Dave (Nov 30, 2018)

The DRO I got is a Heidenhain.  The scales are made from an aluminum extrusion, with end caps sealed to the ends with RTV and screws.  There is a stainless strip for rollers to roll on with less wear, the lip seals, the glass scale, and the slider.

This may not be the fastest way to do it, but being careful not to break the thing was #1 priority.  I did look on ebay for used scales like this one, and I could find them for around $800.00.

First, figure out how much you need to cut.  Check and re check!  This isn't a thing you want to cut 3 times and find it's still too short.

Step 1 - remove one end cap, and slide the slider out, noting and or marking the orientation.
2  -  remove set screws, and slide the lip seals out the end.
3 -   slide the stainless strip out.
4  -  use something to close the open side where the seals were.  I found a strip of metal that slid into the grooves for the lip seals, but even tape would do.

5 - fold up a tissue or the like to keep chips from getting into the housing on the side you want to save, and put it around the glass to fill the space like a loose plug.

6 -  Clamp the extrusion to the mill table.  I chose the orientation that put the glass scale closest to the top, flat way up.  I squared it up to the table so the cuts would be accurate.

7-  use an end mill to cut away the aluminum on that face - one side of the cut should be close to your finished cut length, the other wide enough to leave access to get a Dremel with a diamond cutoff wheel in to the glass.  Make a few cuts, to avoid hitting the glass by going too deep on the first pass.

8 -  Use a slower speed on the Dremel, cut the glass, maybe an 1/8 inch longer than you want.

9  -  Re clamp the extrusion to cut the next side, and repeat for the 3rd.
10 -   you can either make the cuts accurate on the first go, or go back around and do precision after.  The 3 sides you want as clean and square and smooth as you can get.

11-  do the final trim to the glass, leaving it just short of the plane of the end of the extrusion.

12 - I used the end cap, and found a spacer that I could use in the existing holes as a drill guide to drill new holes into the extrusion to tap for holding the end cap on.

13-  drill and tap new holes for the lip seal clamps.

14 - clean out the chips and glass dust.
15 - In my scale there is a spring steel thing that makes a "zero" signal at center, so I slid it to the new center.

16 - trim the stainless strip to length and install.
17 - trim the lip seals to length and re install.
18 - slide the slider back in.

19 - Use non acidic RTV to seal the end cap, and re attach it.

Step 8 was the most nervous part to me, but it was no problem.  I had left 2 of the 3 sides intact to support the glass while I made the rough cut.

I mounted the scale on the front of the table, as mounting it on the back would take away Y travel distance.  I'll figure out how to make a braket to work around the scale for my X power feed stops next.

The process went so well, I could take the 9" piece that I cut off and put it together to use as a short scale if there ever is a reason to collect an extra slider and readout.


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## warrjon (Dec 2, 2018)

I cut the glass scales for my mill on a horizontal bandsaw. I stuffed foam between the glass and aluminium where I made the cut, popped it in the band saw and cut away. You will need to break some of the glass back so the end fits on. Milled the end of the aluminium for endcap and done.

One thing to be wary of, some scales have an index mark, you do not want to cut this. Mine were Easson and had no index.


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