# How to cut a glass scale



## tjb (Dec 9, 2019)

Not sure if this should be a new thread or if I should append it to my earlier thread, 'Need tips on drilling a long thin through hole'.  This question strikes me more as a companion issue, so here we are.

When I added DRO to my lathe, I ordered the glass scale for the z-axis to be slightly less than the full length of the cross slide.  I centered it on the back side with the reader centered between the ways.  Since the scale and reader stick out a little over 2", that orientation doesn't allow close-up use of the tail stock, and constrains access to the cross slide set screw.  I decided to move the set up to the rear of the cross slide - behind the ways - to eliminate those nuisances.  I'm making progress thanks to the sage advice proffered on the other thread - but I'm realizing I now have a second challenge.  I ordered the z-axis scale based on the overall length of the cross slide.  In retrospect, that obviously was unnecessary overkill (rookie error), and now that I want to re-position it, everything would go together better if it were a couple of inches shorter.

Is it possible to disassemble the glass scale, cut it down, and reassemble it and the thing actually work?  I can use it the way it is, but the tail end of the scale would still be over the ways if I don't shorten it - an improvement, but not optimal.

I think I've already managed to make an Alps-sized mountain out of a mole hill on this project and don't want to make it worse by wrecking the z-scale.

This detail strikes me as a little long-winded, but there's a reason.  I thought I was doing our resident experts a favor by significantly limiting the question on the accompanying thread to just the bare minimum: can I get a little counsel on how to drill a long thin hole.  Turns out, I would have gotten MUCH better advice if I had stated the objective along with the question.  Don't want to make that mistake twice, hence, all the detail.

Thanks for any advice.

Regards,
Terry


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## MrWhoopee (Dec 9, 2019)

Never had to do it myself, but I've read it can be done (carefully) on a wet tile saw. There are several videos on Youtube describing different methods.

This guy did it with a 4x6 bandsaw


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## RJSakowski (Dec 9, 2019)

As a matter of clarification, the cross slide on the lathe is the x axis. 

Glass scales have been cut down but it is tricky.  You have to cut the glass carefully so as not to introduce a crack which will enter the area that the pickup head travels.  Cutting glass is not something that I do particularly well.  I would expect that a diamond cutoff wheel with slow feed would work the best.  When drilling glass, a lubricant is used to prevent thermal stresses and I would expect the same is true here.  I'm not sure of the issue of contamination by a lubricant on the working part of the scale though.  As I recall, the last two cm on either end of the scale are not used.

The other issue is proper reassembly of the scale.  Done wrong and it won't function reliably.


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## Holescreek (Dec 9, 2019)

There is nothing to it if you pay attention to details.  The glass is nothing special, you don't even need a clean break. It's easier than window glass.









						New Import (cheap) Dro For The Traytop
					

Finally decided to get a cheap 2 axis DRO for the Traytop.  $220 shipped from Hong Kong with my choice of scale length.  Two things are surprising to me:  First the price included shipping, how the heck do they ship so cheap from China?  It costs $35 to ship a small USPS flat rate box to...




					www.hobby-machinist.com


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## tjb (Dec 9, 2019)

RJSakowski said:


> As a matter of clarification, the cross slide on the lathe is the x axis.


Oops.  Thanks for the correction.


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## tjb (Dec 9, 2019)

Holescreek said:


> There is nothing to it if you pay attention to details.  The glass is nothing special, you don't even need a clean break. It's easier than window glass.
> 
> 
> 
> ...


Thanks.

I'll need to study this.

Regards,
Terry


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## Tim9 (Dec 9, 2019)

I just did it the other day. Easy as hell. There are a couple of good videos on YouTube.  As mentioned in these and various other write ups, the hardest part is drilling and tapping the 4 screws on the end caps. You will need a 1.6-1.8 mm drill bit. And a 2mm tap to rethread the holes. If push came to shove, you could use JB Weld and just glue the cap in place. 
   Other than that... saw the three sides of the scale taking care to not hit the glass. Then lightly score the glass scale with hacksaw blade and bend. The glass will snap. Then go in and using a dremell stone score the glass about 1/4” inside the scale and snap that off. 
   YouTube’s Tinker-John just sawed through the whole damned scale using his bandsaw. I didn’t have big enough balls for that game plan.


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## Tim9 (Dec 9, 2019)




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## JPigg55 (Dec 9, 2019)

If possible, submerge it in water when cutting.
A lot of the problem with cutting glass is the induced vibrations that can cause the glass to crack or shatter. Submerging in water help to dampen the vibrations since the density is much higher than air.


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## Tim9 (Dec 10, 2019)

Submerging in water sounds like it may help. But I try to remember a recent post that I just LOVED. Forget who said it, but...
  He said something like.... “ Paralyzed when I over analyze.”

  The only reason I say this is that after I stuffed the housing with foam as displayed in the one (or both) of the videos, I was amazed how easily the glass snapped cleanly. And furthermore, when I hit the glass scale with Dremel stone to get that glass recess @ 1/4”.... once again I was pleasantly surprised how easily and cleanly it snapped on the scored line put in by the grinding stone.
   I have to be honest here. When I saw Tinker Johns video of how he sawed it with the bandsaw.... I was shocked and thought to myself... maybe he was just plain lucky. After cutting my scale taking much more care, I’m guessing that if I did it like he showed...it probably would have worked just fine.
   If I have to do it again....cut my glass scale for my Z-axis.... I’ll probably just do it the same as I did my last because it really didn’t take that much longer to do than John’s method. FWIW... I’ve watched a few of his videos over the years. He’s no Bozo. He’s a sharp guy who does some gunsmithing and is on YouTube just to help other people. He’s not earning money by posting 3 videos a week....if you know what I mean. 
   But I’d be more worried about submerging the glass housing in water...plus it complicates the vision aspect of grabbing the scale with a rag between the duckbill pliers and the glass..and snapping the scale. Just too complicated in my opinion.
    And...Water, electronics and aluminum just don’t mix in my book.  But what the hell do I know. I personally think that the foam stuffed to stabilize the glass is sufficient. The glass really had a pretty clean break. Scored glass just breaks cleanly. You May have a somewhat ragged edge but the pickup doesn’t come close to the end part of the glass scale. That’s why they add those extra mm’s . That’s why everyone gets the wrong size.  
   Anyway, to each their own. Bottom line is...tapping the holes is hardest part. Cutting glass was much easier than I thought it would be.


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## JPigg55 (Dec 10, 2019)

Yep, kind of like "Measure twice, cut once".
It usually boils down to the "Risk/Reward" option. I'd definitely take more time an consider more options if the end result failing meant trashing a couple $Grand$ vs  a "$Couple hundred$".


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## Winegrower (Dec 10, 2019)

I have had good success cutting 6mm glass rods (not scales, particularly) by making two brass bushings an inch or so long, and just the right bore size to slip over the rod.  Score the rod with a triangular file between the bushings, separate the bushings by a mm or two, and then bend by holding onto the bushings.  Snap.   It's a pretty clean break, and I've never had a failure with this method.


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## Winegrower (Dec 10, 2019)

Using a bandsaw on the whole assembly is just crazy lucky, seems to me.


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## FOMOGO (Dec 10, 2019)

I don't know. Two out of two successful cuts, by several different people seem like pretty good odds to me. Having cut hundreds of feet of tile, and glass with a diamond blade on both a 10" wet saw, and with a 4 1/2" diamond blade on an angle grinder and a wet sponge, I would be more inclined to go that direction. I don't see the water being an issue. Your not really dealing with any electronics when making the cut, just blow it out with air after making the cut. Mike


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## Holescreek (Dec 10, 2019)

A couple things to keep in mind:  You're going to cut the glass scale just far enough inside the end of the extrusion so the end cap will fit back on.  The point on the scale where the reader head sits (when it is at the end of the scale) is going to be an inch or so further in from the end cap.  The cut need not be perfect or even straight.  I've never seen a glass scale shatter because they aren't tempered.  Don't over think it.


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## MrWhoopee (Dec 10, 2019)

Holescreek said:


> Don't over think it.



You're kidding, right? It's what we do.


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## tjb (Dec 10, 2019)

Well, it turned out okay.  I used a Dremel to cut as much of the aluminum as I could, then stuffed it full of wadded up shop paper towels pushed in with a small screwdriver (being careful to not dislodge the glass).  Took it over to my vertical bandsaw and finished the cut - no issues at all.  Then I took a small cone shaped grinding tip on Dremel and very carefully and slowly ground a spot on the glass about 3/8" inside the end.  I used needle nose pliers to break it off and clean it up.

Totally uneventful - just the way I like it.

Thanks for all the tips and links to videos.

Regards,
Terry


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## tjb (Dec 10, 2019)

Oh, yeah.  Forgot the final step:  I intentionally overcut the length by about a 16th of an inch.  Took it over to the mill and cleaned up the edge.


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## MrWhoopee (Dec 10, 2019)

tjb said:


> Oh, yeah.  Forgot the final step:  I intentionally overcut the length by about a 16th of an inch.  Took it over to the mill and cleaned up the edge.


I'm assuming you mean the aluminum housing.


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## Tim9 (Dec 10, 2019)

Like I said.... it’s not the water so much. It’s the fact that I think it might be hard to manage snapping the glass while under water... in a tub long enough for a 16” scale. And then yeah...one would have to get all the water out afterwards. And probably make sure that their water isn’t loaded with minerals which could possibly interfere with the glass scale.  Dried calcium spots could be an issue. And of course, as long as you clean it real good, it’ll be fine. All I’m saying is, if you need to cut your scale, just watch the videos and don’t be scared to do it. It’s really easy. But you’re going to need a 2mm tap. I got my tap off of eBay. Nothing high end. Used a 1.8mm drill bit. They were crap. Ended getting 3 holes drilled and blew off the forth. All and all, it’s really pretty easy. Watch the videos and do what ever method you’re comfortable with. I know I was really apprehensive at first but all that worry was for naught. 
I used decent quality duckbill pliers. I really would rather not submerge my Knipex pliers under water. Let’s face it...the Chinese scale cost @ 50.00. 
   Paralyze because of over-analyzing. I can do that too often. 

  It really did snap clean when I held one side with pliers and snapped other side with pliers. All jaws of pliers had shop cloths insulated where contacted to glass.
  I only have 2 hands. Trying to do this under water just seems overwhelmingly complicated in my mind. If I had an extra set of hands....yeah, I can see that maybe working.  But is it really that necessary ?


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## tjb (Dec 10, 2019)

MrWhoopee said:


> I'm assuming you mean the aluminum housing.


Yep.


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## Latinrascalrg1 (Dec 10, 2019)

FWIW......One of those single diamond in the tip grinding wheel dressing tools work Great at cutting glass.  Plus they are very inexpensive and one will last you a very very very long time if you use it strictly to cut glass.  I find they cut tile as well which makes it a handy tool to keep in the old handymen tool box.


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## DanLins (Dec 11, 2019)

I used one of those 1" diamond cutoff wheels in my Dremel a couple of years ago to shorten mine, worked great. A little water judiciously squirted during the cut and it went through like butter. As mentioned above, drilling and tapping the newly exposed extruded aluminum took more pains. I had no metric taps, so I simply ran with some #4-40 screws I had laying around.

Seems weird how many Youtube video makers have  gotten away with using a band saw blade.


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## Tim9 (Dec 11, 2019)

Glad it worked out Terry. Just like you said...really uneventful. More worry about it not working but in the end, it’s pretty easy.

*added edit note:  *the original scales have some sort of silicone sealer on each end and little green beads about 1/16 thick @1/4” long to hold the scale into the track. I was going to add a dab of silicone to the end of the new length on my scale, however I did not have any of that special silicone sealer which doesn’t attack electronics. And I was worried about normal silicone attacking the pickup while said silicone cured.
  So I just put it together without any silicone. In all honesty, I had planned on getting/ investigating proper sealant for this. Maybe a polyurethane type sealant. Not really sure. Anyone have any ideas. I caution regular silicone because I remember that the regular stuff would attack O2 sensors on automobiles. But I’m going back 20 years here.... and honestly forget all of the specific details.


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