Cheap DRO for Mill

Hi Guys,

I own a CX600 Mill (**LINK**  and i am considering putting a DRO on it.

Now you can spend alot of money on a DRO and you can also get cheap ones from China such as the one i have linked below. Firstly what is the difference? Accuracy and resolution looks good, so what are you getting with a more expensive one.

Also, i am a hobby machinist so whilst i want something of quality for the home use, i am not doing this day in and day out for a living so trying to strike a balance.... anyway, i value your opinions and options. Here is the link to a Chinese version..

**LINK**

Do a search for DRO. Lots of posts already on MEW.

I use similar (Warco versions) in 3 axis form on my WM16 mill and 2 axis on the 250V lathe, both work fine.

An industrial DRO should withstand coolant and swarf without loss of function and be reliable over a long period. You also get guaranteed accuracy with an industrial DRO. I got calibration certificates for the sensors with my DRO. Personally I wouldn't believe the accuracy specifications in the link. For a start accuracy and resolution are the same, which is not generally the case when taking measurements.

A cheap DRO may well be adequate, it depends upon the real accuracy that the user actually needs.

Andrew

What makes a difference to a DRO is the how well built and protected the scales and electronics are, and to a lesser extent the features offered. For high-precision work, different types of scale technology are available. A high-end DRO will be mains-powered, with well-sealed scales, smooth action, and bullet proof electronics.

In comparison, I bought a pair of Warco's cheapest and fitted them to my mill, an easy job. The scales are battery powered lasting 9-18 months and each scale has it's own readout unit, a simple plastic box with a magnet on the back, with a a small unlit LCD display. The display is inferior to the nice combined XYZ and keypad units that have to be bolted to the head. The scales are unshielded and must be vulnerable to coolant. Reset accuracy OK - within ±0.02mm. Perhaps because I don't often flood cool, the scales work fine: after 5 years an occasional wipe with a tissue has kept them in good order. The only fault was mounting the displays on the motor control box caused one of them mismeasure when the motor was turned off. This turned out to be due to contactor thump shaking a slightly loose USB connector: moving the displays fixed that, but note USB connectors aren't supposed to wobble! Otherwise the DROs turned out to be a bargain: they make a huge difference to milling.

However, despite satisfaction, when they fail, I'll go up market. Although they've been reliable, the vulnerability of the scales is a worry and I don't entirely trust them. (Causing time-wasting double checking). The batteries are a pain, and the display hard to read and inconvenient compared with a combined unit. Although the scales provide 'good-enough' accuracy for most of what I do, improved accuracy would save time when being spot on matters. I rarely work outside a 200x150mm footprint, and the DRO is accurate within that range. I'm not so sure it's good to ±0.02mm across the entire travel of the table, about 550mm.

As a hobbyist my experience with this DRO has given me confidence in the very basic breed. But they wouldn't do in a more demanding workshop. Chaps who need to crack on would be frustrated by the hard to read displays and tiny buttons. Keeping an eye out for misread measurements caused by mucky scales or dying batteries slows everything down. Having confidence about the accuracy of large movements might be vital. Most of this can be fixed by doubling or tripling the budget.

If you really need the very best, buy from a professional supplier. Not many do, the very best is very expensive.

Dave

I would most certainly advise against buying cheap chinese from bang good. If there were to be a problem you might very likely be able to kiss goodbye to your money.

What they are selling is likely to be iffy on quality, if not rejects from more choosy wholesale buyers. And their customer service reeks (past experience).

Cheapest is usually (but not always) not the best deal.

I once bought a bullet camera from china on which the voltage dropper slowly got warmer and warmer, then it got hotter and hotter until I junked it on safety grounds (before it melted, or worse). Got my money back through epay or paypal (all one, now) but the supplier was not prepared to budge before I made the claim for a refund. I think they just hope the buyers who get the dodgy items won’t make waves. Epay are probably quite aware of the numbers of claims on some of these items or suppliers, but still carry on collecting their sales commissions, all the same.

I still buy from China, but am as selective as I can be. It can be better than buying the same item from a “UK location” (at increased cost) sometimes. I recently wanted an item at short notice, but it took about 10 days to arrive from Portsmouth (I think). It would have arrived just as soon, and at reduced cost, if ordered direct from China. I suspect that they were not stocking the item at all.

My Chinese DRO has error compensation facility. I never had cause to use it since the DRO is more accurate than the machine's rigidity allows for, but if you were so inclined you could map the scales with jo blocks or indicators and apply the compensation in the DRO.

I Have similar from Arc Euro bought & fitted some time ago; can't complain about performance, battery life length &, as SOD's comment I rarely work out of similar footprint so can concur with all of his findings, should finances vastly improve then I would go up market with something from DRO but as things are I'll continue with what is fitted. For fitting pics see my album 'DRO'. Usual disclaimer applies.

**LINK**

George.

Well thankyou for everyones comments, i appreciate your time to respond.

So some of you are showing you have the most basic of DRO's like the Warco version and they essentially 'do the job' for us model engineers...yet would like to upgrade given the chance. So i guess this leads me to the thought of 'If you would buy again, what would you get'?

I don't mind putting a bit of extra cash where it makes sense, but i equally dont want to go overboard and don't have the means to anyway! (The wife may apply restrictions!). For reference i am located in Canada so i am not necessarily looking for a British supplier, althought thats ok if it makes sense.

Thanks again

Cheap scales don't give you the basics for a DRO on a Mill, if you don't have multiple zeros then you don't have a DRO and you might think it's great because you will simply not understand the advantages to having multiple zero points in 3 axes.

We fitted the same units to my son's mill but use them with Touch DRO (I replicated the design of the Arduino based unit on stripboard) so that an Amazon Kindle Fire acts as a touch screen display.

Brian

Multiple zero's can be (and usually are) done in the DRO independently of the scales.

Years ago, before the plethora of relatively cheap systems available from the far east, we were building our own based on the Shumatech design. Cheap scales (often cheap cut-down calipers) were all that were practically available for many people. Yet we certainly used multiple zeros.

I'm still using my Shumatech DROs - albeit with optical scales in one case.

Many of the cheap DROs come without any instructions for mounting the scales and read heads. If you have not set up a DRO previously I suggest watching some of the videos from DRO Pros.

**LINK**

I wouldnt worry about having no instructions a 5 year old child can work it out.

This is one difference in cheap scales 0.145mm error on initial take up. Means carriage moves 0.145mm without the cheapy registering!

There are some much better instructions for the "Sino" type DRO units.

I can't paste PDF here, but if any one wants them, message me your email.

Jim

If you look on Ebay for a seller 3977colin CBR Electronics Ltd he is from Nottingham and sells loads of DROs he goes all over fitting them he is a loverly chap and has done 2 mills and 2 lathes for me over the years at a very good price.

Bob

I started with the less expensive X and Y scales from ARC. I'm not knocking ARC in any way, these are sold by numerous outlets.

Out of the box one of the scales would not work with one display but swapping over the scales and displays fixed that. These were also unreliable - trying to creep up on a number e.g. 2.00mm was often frustrating because I'd get to 1.99 and the display would jump to 2.01. Also the wiring I believe is not shielded and is affected by close proximity to mains cables and sends the display haywire, meaning loss of a datum and having to edge-find all over again.

I've now splashed out on a 3 axis DRO and two scales for X and Y (Z axis will possibly come later) from Machine-DRO. I got a lot of brackets I didn't need and have made custom ones to fit my WM-16 mill. These are magnetic scales and I love the setup, especially the SDM function for pre-setting positions of multiple holes or operations.

My understanding is if I'd gone for more expensive glass scales I could have had an extra feature for setting a machine datum which allows for position(al?) recovery after switching the DRO off and back on. e.g. overnight . I don't think this feature is possible with magnetic scales due to a lack of an in-built reference point.

Regards,
Ed.

Criticism of the display jumping as described is a little unfair in that it seems bad rather than being a real problem. The accuracy of most basic scales is typically 25 micron, or 0.025mm. So the display jumping 0.02mm as you creep up to a measure isn't surprising and despite appearances the result still isn't so dusty. 0.02mm is rather less than a thou. The easiest thing is to ignore display jumps unless you're doing something requiring special accuracy - a difference of 0.02mm is often small enough not to matter. If high-accuracy matters, double check that whatever scales and display you buy are actually better than 25 micron, many aren't. Also, unless you own a hot machine in good condition, it may not live up to the promise of a high end DRO display and expensive scales.

When my cheap scales die I'm going to open the wires up to see if they're shielded or not. I had suspicions about shielding when mine misbehaved but I couldn't recreate the fault by putting the wires near mains cabling. In my case the problem was a loose USB plug vibrating mechanically. However, a loose plug might not be properly shielded, explaining Ed's symptoms. Certainly we agree the USB side of these units isn't covered in glory!

Despite shortcomings, even a simple DRO is far better than driving a mill on the mechanical dials. The inexpensive Warco scales may not do PCD calculations or be highly accurate, but they eliminate operator mistakes caused by misreading the dials or forgetting to allow for backlash, and even the cheapest DRO can do Imperial and Metric.

Dave

Edited By SillyOldDuffer on 23/04/2019 17:30:54

I've had the cheap oriental stuff on my mill for some years now. In the beginning I found that the XY readout positions were very, very unreliable and kept jumping erratically. One minute I'd be at 2.250" and the next, and without moving the axis, I'd be at 6.090" say. After much probing and experimenting I could not discover the cause but I DID suspect that the DRO strips were being affected by stray lectric stuff.

I uninstalled the steel DRO scales and reinstalled them on blocks of PVC completely isolating them from the mill castings.

Did it work? I’ve not had a problem since! So I think that for the average hobbyist these cheapo scales are OK given the aforementioned problem and solution.

While we are here, I find that the XY display eats its lithium cells if I forget to turn the display of (which is more often than not).

Rik

I agree with both Ed and Dave.

I have examples of all three types. The Arc ones are not quite as stable as the Warco offering (which are bomb-proof in that the readout remains rock steady), but were cheaper. The Arc ones run on mains leccy, while the Warco ones are battery only. Swings and roundabouts - they are both good enough for the applications and likely better than my machining! They are certainly good aids, but one needs to understand their limitations (accuracy and precision) if needed for very precise measurements.

The comprehensive dro is in another league altogether. It has a further significant figure readout, which means that if the last digit changes by a couple of points it is naff-all for my work! There are things it will do that I will never ever use, does calculations on board and will store umpteen point settings, etc, etc.

They are all better than the mechanical indicators and can instantly work in the choice of metric or imperial units at the press of a button. The only downside is fitting them where they are protected without reducing access for some workpieces, or without reducing table travel (particularly cross travel) on mills. For lathes, they can complicate adding things like taper turning attachments and take up some tailstock travel if fitted to the carriage.