DRO Scale Recommendations (for TouchDRO, and other DROs)

[ycroosh]

Good day, folks.
I get a lot of questions about scale recommendations for TouchDRO, so for the last couple of weeks I've been testing a bunch of different scales. I intend to keep an updated list on my website: Recommended DRO Scales, but I think there is value to having a thread here.
This is applicable to any DRO, not just TouchDRO (modern scales are all compatible, except the pinout. If you can solder, you can often mix and match scale brands with traditional DRO as well).

So, here are my findings:

Optical scales (AKA Glass Scales)
I have not come across an inaccurate optical scale. If they work, they are accurate. The reason (I think) is that the important bits are made by big companies, so discount suppliers can't cut corners there. Low-end stuff usually has cheaper electronics (I've seen PCBs that must have been made by kindergartners). They usually skip any sort of QA, so you are more likely to get a completely dead scale. Worst case scenario are cold solder joints, where the scale looses connection intermittently. I have run into one of those myself.

As far as brands go, I have a lot of experience with Ditron over the years. They were one of the first to offer inexpensive glass scales (along with Easson, which is now out of business). My experience with the company is very positive. The build quality is very good.
People who use Aikron tend to like them. I can't comment about Sino, but the one scale that I have is very well made.
As far as I can tell, Ditron, Sino, and Aikron use the same components, and the pinouts are identical. Ditron and Sino are OEMs (they make their own stuff; Aikron might be a reseller, but I'm not sure). In general, I would call those three to be "premium" Chinese DRO brands for optical scales. (I will discuss magnetic scales later; they are different story)

There are two more common component sets that are used by lower tier sellers. It's very likely that there are two companies who make cheaper DROs and white-label them for various companies. In the USA, Vevor scales seem to be pretty decent discount scales (for the price). The specimen I got is well put together, but I have heard of people getting dead scales. Vevor's customer service appears to be VERY bad, though. There are identical scales sold on Amazon.

"ToAuto" branded Scales on Amazon are very decent. I have two. Electronics are very well made, and the cables were assembled surprisingly well.

Magnetic Scales
The story with magnetic scales is complicated. I personally avoid them, unless I don't have any other options. There is a lot of very aggressive marketing that portrays them as magical, and a lot of people report that they "work very well". In practice, these scales were not intended for general DRO usage. if you read the literature from Magnescale (now owned by Sony), the problem they were solving was "scales for extremely high vibration environments, or for environment where high pressure flood cooling or immersion cooling is used". Magnetic scales have to do a lot of "magic" that is very expensive. Whereas the resolution is baked into optical scales (5um optical scale has encoder trip etched with 20um moire pattern, and it's not going anywhere) a 5um magnetic scale has to split sine/cosine signal pair with 5mm period into 5000 discrete steps. If the tape is not magnetizer perfectly, or the distance varies, or a metal chip gets between the tape and the Hall effect sensor array, accurate goes out of the window.

All this said:

Electronica/EMS scales are "OK". In my testing 1um and 5um scales have pretty much identical effective resolution. I would call them "reliably +/- 10um". This is in-line with what EMS states in their documentation for bot versions. Out of the scales I tested, Electronica (I have 4 specimens) scales were very consistent and had very small amount of cyclic error.

I tested 7 Chinese magnetic scales, and the best one had 0.0045" worth of cyclic error (see the first graph at the end of the post). This one is 5um "slim" made by Ditron. Full size Ditron 5um were about the same (see second graph). I tried Aikron and the scales that Little Machine Shop sells. Aikron was on par with Ditron. LMS had 0.0072" of cyclic error. I have a 1um Ditron scale that I haven't tested yet, so to be determined if it is any better.

The last graph shows Chines 5um scale (amber line), EMS 5um "MagnaSlim" scale with ride height set to 0.1mm (blue line) and 0.5mm (green line).
(Sorry for different graphs. I wasn't planning to attach them, so the screenshots are not using the same units)

In short, I would use EMS scales in a pinch (I am, in fact, installing a 1um scale on my cross slide, since I don't have any other viable options). For my purposes 1um EMS scales to be the bare minimum entry level magnetic scales (the price difference with 5um is not worth it, and 1um models have better repeatability). I would not use 5um Chinese magnetic scales of the current generation, unless you have a very large lathe and use it to machine locomotive wheels, where +/- a few thousandths is not an issue.

For fairness, I talked to Ditron engineers about the error, and they assured me that it was my technique. Ditron provided test results for similar scales that look much better than mine (still not even close to the nominal resolution, though). The last two graphs are from Ditron (I have their permission to share the graphs). Curiously, I get better repeatability than their testing.

I hope this information will be useful for some of you.

Regards
Yuriy

 

[WobblyHand]

Thanks for publishing this. Very helpful for the HM community.

 

[buffdan]

Thanks for sharing Yuri. Very interesting. Any similar error/accuracy data for glass scales?

 

[rabler]

Interesting to see some actual numbers around the accuracy of these magnetic scales. No where near as good as you would think with resolution claims of 1 and 5um. Lathe cross slides would seem to be a common case for using magnetic scales, where space is the most limited and cut to length is beneficial. And also a case where accuracy and resolution are more critical as far as home/hobby machining.

My TouchDRO unit should arrive today or tomorrow depending on the whims of USPS. Haven't yet ordered scales so this is timely.

 

[ChazzC]

Thanks for the updated (and detailed) information, Yuriy. I also checked the updated page on your website.

That said, I have recently purchased additional iGaging Absolute DRO Plus capacitive scales for my attempt at adding them to my 7 x 16 Mini-Lathe: none of the other scales I have found look like they would work well with the limited space available on the 7 x lathes, and I have been very pleased with the iGaging scales work with TouchDRO on my Mini-Mill. I'll keep you (and the Forums) updated as this project progresses.


Charlie

 

[Nesse1]

Another thanks, Yuriy.

I've read in some of your previous posts, or maybe it was on your website?, that you like Glass scales. Unfortunately, those are just too large to fit on my 12x36 lathe cross-slide, so magnetic is the only option.

It seems that the trend is towards magnetic, but then again, I'm not sure. Has development of glass scales stopped? Any idea what the future holds?

 

[DavidR8]

And here I was all set to order mag scales for my mill.

 

[RaisedByWolves]

And here I was all set to order mag scales for my mill.

Yeah, now Im lost all over again.

 

[DavidR8]

Yeah, now Im lost all over again.

Now this may seem like a silly reason to go magnetic but having installed two DROs already, the last being on my Clausing lathe the appeal of adhesive scales is pretty big.
I do have some kick@ss 3M double sided tape that I used to stick on the cover on my Z lathe scale.

 

[ycroosh]

Another thanks, Yuriy.

I've read in some of your previous posts, or maybe it was on your website?, that you like Glass scales. Unfortunately, those are just too large to fit on my 12x36 lathe cross-slide, so magnetic is the only option.

It seems that the trend is towards magnetic, but then again, I'm not sure. Has development of glass scales stopped? Any idea what the future holds?

I don't think glass scales are going anywhere any time soon. In the 5um and 1um space, the technology hasn't changed since it doesn't have too. In the past, the encoders were made via photolithography process (which was pretty expensive). New scales are laser-etched, which these days appears to be dirt chip. The reader head is an over-the-counter part these days.
Heidenhain is doing some cool research with hybrid technology that uses glass scales with built-in laser interferometer to get sub-micron resolution.

Magnetic scales have their uses. I think we are seeing more of them for a few reasons:
1. DRO Pros used to sell EMS magnetic scales and glass Easson scales. Once Easson went out of business, DRO Pros started pushing EMS scales very aggressively (and actively bashing glass scales for being too sensitive to contamination)
2. SIEG figured out how to use very cheap magnentic scales with TouchDRO (LMS still sells those) about 4-5 years ago, so other Chinese manufacturers followed suit. 5 years ago it was next to impossible to find these scales; now it feels like my local 7-Eleven will soon carry them.

I think the main reason is that they are much cheaper to produce and store than glass scales. Good magnetic scales use proprietary (still under patent) interpolation electronics and consistent and stable tape is pretty expensive. The electronics that Chinese magnetic scales use were [probably] intended for motor control with much coarser resolution. For example, EMS scales use 2mm pole-to-pole tape for 5um and 1um heads, so 5um heard is in fact de-rated 1um head. This is the reason that both of their models have the same stated "accuracy".
Chinese scales use 5mm tape for 5um heads, and 2mm tape for 1um heads, so 5um head has worse error than 1um version.