Could I get a history lesson and guidance about dro's?

[shild]

Looking to get myself a DRO. I'm going through them on ebay and seems like older ones seem to keep their price compared to some of the new ones with more features like this one for $89 for example. https://www.ebay.com/itm/2-Axis-Grating ... 4902.l9144 Is this one not very accurate? Or does accuracy all depend on what scale you use?

[John Evans]

2 things do NOT buy a used DRO unless you can confirm it is fully functional. Second buy a complete package/system from a US based supplier. Unless you know what you are doing don't buy the display from one source and scales from another,as many systems are not compatible display-scales with each other.Not something you want to do on the cheap !

[shild]

Unless you know what you are doing don't buy the display from one source and scales from another,as many systems are not compatible display-scales with each other.Not something you want to do on the cheap !

Is this just because some older ones take unusual looking connectors? Because if voltages are the same I'm not afraid to chop and solder on a new connector. I found myself a vintage dro that's very good looking!

[WesHowe]

Here is a very specific discussion about DRO scales on Practical Machinist:
http://www.practicalmachinist.com/vb/ge ... nd-336490/

A lot of the newer Chinese-made DRO scales are more compatible with other readers, since they all seem to be copies of each other. Even there, you have choices to make between glass and magnetic scales, 5 micron or 2 micron resolution, and so on.

I am guessing price is a big issue here. Used DROs are a crap shoot, check the return policies carefully. I would not recommend the smaller 1 axis scales with the little LCD display if you want to do decent work. You can't depend on them to better than 1 thou accuracy, and a lot less if you are moving a few inches. The skip counting steps sometimes, such as a rapid traversal, and frequently when you get back to zero you find you aren't at the same place you started from.

You can get a brand new Chinese 2-axis DRO with shipping for under $250 (to the U.S. anyway). Glass scales and 0.005mm resolution (approximately 0.0002 inches). A year ago I paid almost twice that for a similar Chinese DRO; if it broke I'd buy a new scale or head rather than do without. But so far it's worked fine.

- Wes

[shild]

Here is a very specific discussion about DRO scales on Practical Machinist:
http://www.practicalmachinist.com/vb/ge ... nd-336490/

A lot of the newer Chinese-made DRO scales are more compatible with other readers, since they all seem to be copies of each other. Even there, you have choices to make between glass and magnetic scales, 5 micron or 2 micron resolution, and so on.

I am guessing price is a big issue here. Used DROs are a crap shoot, check the return policies carefully. I would not recommend the smaller 1 axis scales with the little LCD display if you want to do decent work. You can't depend on them to better than 1 thou accuracy, and a lot less if you are moving a few inches. The skip counting steps sometimes, such as a rapid traversal, and frequently when you get back to zero you find you aren't at the same place you started from.

You can get a brand new Chinese 2-axis DRO with shipping for under $250 (to the U.S. anyway). Glass scales and 0.005mm resolution (approximately 0.0002 inches). A year ago I paid almost twice that for a similar Chinese DRO; if it broke I'd buy a new scale or head rather than do without. But so far it's worked fine.

- Wes

Some of these used vintage dro's are so good looking I'm very tempted to do the crap shoot! I'd rather have one with switches and knobs than one with buttons that feel like a cheap flip phone! If you can think of certain models I'm very open to suggestions right now. Very open to what scales to buy too. Do the finer resolution ones trade off dependability for resolution?

[WesHowe]

All I tried to do was put the "old versus new" in perspective. If the old ones are working as they did originally, people made a lot of sophisticated parts with them. Personally, I would no longer enjoy spending the needed time with an oscilloscope or a signal analyzer to determine what works and doesn't. However, I'm not you and if you have a good adventure doing it, take pictures and tell us about it!

- Wes

P.S. Go to you profile and put in where you live. If it's a bitty town outside a major city, just put in the major city. So we have an idea what area you are in.

[pete]

I dunno, that Ebay add reads odd to me like it's a semi ok translation from the original Chinese or Indian but still not quite right? There using some terms that sure aren't in my newall user manual. "5 bearing system"? "grating"? I think I know what they mean but do they mean what I think they do? And those would be terms used for the scales / reader heads and they seem to be only selling the display. "accuracy class"? Wot's that? The +- 1 um I get, but is that it's actual real world capability, or is that just the displays resolution? Accuracy and resolution while somewhat and barely related aren't the same thing at all. And accuracy is a function of the scales and reader heads quality and accuracy, and the displays correct processing of the signals it receives. I certainly wouldn't call it an "electronic scale" in that Ebay add since it's only the display unit for the electronic scales and reader heads. And I've yet to see where good dependable accuracy wasn't directly reflected in the price. You don't say what you want to put the dro on and there were some very well made displays and scales made. Depends on the vintage, brand for what it will do for the used one your looking at. Some or most of the newer displays in the last 10-20 years have a lot of very handy features built in that may not seem that important now, but depending on what your doing may be very important later. Tool offsets, pcd for bolt holes, multiple zero points etc. I could easily be wrong of course, but for $89 I have real doubts there's going to be any back up support if there's even one problem. I'm old enough now to have finaly learned there's no such thing as good, accurate and cheap. It's simply impossible no matter where in the world the products being made.

Accuracy and repeatabilty are the two most important terms when it comes to metrology equipment. Resolution is simply how many zeros there are after the decimal point. You could have a display resolution showing to 1/millionth of an inch and scales that are only good to + - .001" So your actual accuracy is only somewhere within .002" no matter what the display says. And if it can only repeat a measurement to + - .005" every time it's going to be somewhere within .010" of being correct. Industry standard for accuracy with good equipment is usualy + - one count. Example, a .0001" reading micrometer should be accurate to + -.0001". Afaik there's no change in durabilty with better ACCURACY scales and reader heads. The glass scales are a bit less durable than some types of magnetic scales such as what Newall uses. So the guarding and seals for the glass scales needs to be in good shape. If the glass scales get scratched you can do permanent damage to them. Even dust and dirt can affect the readings. The glass scales work just fine if there kept clean and well protected. Personaly for something like a new dro I'd want to be buying one that has some type of proven track record. Sino, DRO Pros would be my minimum I'd settle for. Used? A whole lot of the older models are no longer supported by the big names in industrial quality dro's. But if your good with electronics and can fix what I sure can't, Acurite, Sony, Mitutoyo, Newall, Heidenhain etc all made very good quality and accurate systems. I think but don't know for sure that Newall scales and reader heads will work with any Newall display they made. Mitutoyo made, still make? plug adapters so Newall magnetic scales could be used on some of there displays. I'd double check all that tho. And Heidenhain have a reputation for being tough to find repair parts for the older models. Since I've never owned one I can't verify that's true or not. I'm 100% in agreement with what John said about only buying a used one if you know for sure the whole system is working as it should be. And with my limited electronics understanding I believe there's at least 3 or more different signal systems in common use for dros and the reader heads and they all aren't compatable with each other.

[shild]

Thanks Wes, thanks Pete! I just got myself a fascinating looking specimen from Valeron Digital Techniques. Can't find a build date but looks mid 70's. It's only a single axis readout yet it has a "Probe A" input and a "Probe B input. Is this so that a scale can be put on the head and one on the quill? https://www.ebay.com/itm/Valeron-Digita ... 2749.l2649 Oh yeah, Pete, you wanted to know what I'm going to put the dro on, I'll probably start by putting it on my mill drill table then move it to the lathe when I get a better dro for the mill then maybe move it to a height gauge if I get a better dro for the lathe. But at the moment I don't even know what scale to buy for it. Do you?

[pete]

Probe A, probe B input it's for sure not a display for a dro. It's some type of display for a gage. They used items like that for measureing coatings, paint thickness or a hundred other things. See if you can track it's use using Google.

[pete]

Double post.

[pete]

Fwiw I spent a bit of time checking prices on an entry level but proper dro. Precision Matthews offer a 2 axis system with 8" x 22" scale travels. Depends on how they measure there scales, but you have to add half or sometimes more of the reader head length at each end of the machines travels what ever they are to have the scales cover the machines full travel. $350.00 Yes to some that sounds like a lot. One way or another this hobby is and always will be expensive. I paid $3800 for my 4 axis Newall system and micro syn scales. Even if you value your time at almost nothing your going to be into a real but used system for that or more unless you get very very lucky. And there's no way to tell how long it will work or if you can find the repair parts if it does fail. I don't see where anyone is going to sell a properly working used dro and scales for less than $350 today. If it was priced less than that? You can bet somethings wrong that there not willing to admit to.

[shild]

Probe A, probe B input it's for sure not a display for a dro. It's some type of display for a gage. They used items like that for measureing coatings, paint thickness or a hundred other things. See if you can track it's use using Google.

It's not the fact the decimal is so far to the left that makes you think it's only good for measuring coatings is it? Because there is a decimal between all the other digits too, but I haven't lit all those up yet. By the way, I took the top cover off to see inside, looks like of the 8 holes for each probe only 4 of them actually have contacts. It has 5 circuit boards, one for the LED display, one for the preset limits, one for the back panels switches and plugs, one parallel to that one and a motherboard flat on the bottom. The motherboard has 2 dipswitches on it, don't know what they do yet. I'll see if I can get pics or a video up of me playing with it later.