DRO Scale Recommendations (for TouchDRO, and other DROs)

buffdan said:
Thanks for sharing Yuri. Very interesting. Any similar error/accuracy data for glass scales?
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Glass optical encoders don't have non-linear error. Modern scales use moire effect. In simple terms, the encoder strip has marks etched at 20um or 4um on one side. The reader head has a matching set of marks 5-10mm long. It uses IR emitter on one side, and IR-sensitive photo transistors on the other side. When the marks match perfectly, the scale reads "1"; otherwise it reads "0". Any measurable non-linear error would result in a dead spot on the scale (since the patterns would not align).

The thing that can add inaccuracy is slop in the mechanical coupling between the machine and the reader. I encountered one scale where the manufacturer skipped half of the ball bearings, so the encoder was not tracking straight. Machine vibration caused wild jumping in readings.

One day (when I get a bit of time), I will either make a video about glass scales, or at least post some photos here.

Regards
Yuriy
 
FWIW, I have cheap mag scales on my small machine and I did a test with touch conductivity and always came out with @ .001 accuracy in repeatability. For what I do, that's plenty accurate. I got past my desire to be perfect after I got married.
 
Inferno said:
FWIW, I have cheap mag scales on my small machine and I did a test with touch conductivity and always came out with @ .001 accuracy in repeatability. For what I do, that's plenty accurate. I got past my desire to be perfect after I got married.
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Repeatability is pretty good with all magnetic scales I tests. it's the cyclic and "random" error that is bad. To test for it, you can take interval readings with a good analog dial indicator, and compare them to what the DRO shows.
 
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@ycroosh
I bet there's a lot of people who would buy scales that you recommend. An affiliate link to Amazon scales would earn you some cash, and give some folks a sense of comfort in buying something you've tested.

It's possible you have a reason to not do that; please forgive me for the unsolicited advice.

Also, thanks for mentioniong brand names; it makes the decision much easier.
 
PNW_Guy said:
@ycroosh
I bet there's a lot of people who would buy scales that you recommend. An affiliate link to Amazon scales would earn you some cash, and give some folks a sense of comfort in buying something you've tested.

It's possible you have a reason to not do that; please forgive me for the unsolicited advice.

Also, thanks for mentioniong brand names; it makes the decision much easier.
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This, all day.
 
Really appreciate this discussion. My mill has space for glass scales, but I was going to go for magnetic scales like I used and installed before. After reading this, I've got some Ditron scales on order at 1/3 the price, and hopefully better accuracy.
 
I made a typo in the original post (1um vs. 5um slim Ditron scale). I tested 5um slim and full size scales, but in the text I typed "1um slim". The original message is now fixed.
 
Just ordered Ditron 5um glass scales and the option B box for my mini mill.

I have enough space and the magnetic/glass issue was more expensive this way, but its only money.

I wanted the Aikron scales, but the $70 shipping charge made me cringe.
 
I am having all kinds of problems with my Ditron 1um cross slide scale. I am measuring it against a DTI and 123 blocks. It repeats to zero well and measures perfectly at some distances but intermediate distances are sometimes way off. By that I mean .0015". That is well out of spec and too much for a cross slide. I think this is what Yuri is describing.
Right now I have no idea where to go. Is there a small/slim glass scale I should be looking at?
 
rwm said:
I am having all kinds of problems with my Ditron 1um cross slide scale. I am measuring it against a DTI and 123 blocks. It repeats to zero well and measures perfectly at some distances but intermediate distances are sometimes way off. By that I mean .0015". That is well out of spec and too much for a cross slide. I think this is what Yuri is describing.
Right now I have no idea where to go. Is there a small/slim glass scale I should be looking at?
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Is this 1um magnetic scale?
 
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