Cheap DRO

[Cogsy]

I've been dreaming about a DRO for my mill, even though there's no way I can afford one, and I was having a look at the Chinese stuff on ebay. I've found a remarkably cheap 2 axis unit - $272 AU shipped - and I'm wondering if anyone has any knowledge/feedback on it. There's very little info from the seller so I'm hoping someone knows about it just from the picture :hDe:. Here's the LINK. I still can't afford it but if they are good units available at this price I may have to look at selling some stuff and trying to get the cash together.

 

[Ghosty]

Al,
I have seen those as well, the size of the scales(width) will be the problem I think. The read out will be about as good as any other.

Cheers
Andrew

 

[Blogwitch]

Al,

I wouldn't worry too much about the quality or reliability, most of the ones in your local shops and distributors come from China now.

The only thing you have to look out for what features there are in the display head, the more expensive ones usually have a few more of them, but even the very basic ones will have more than enough for working with. Just make sure that the glass scales come with protective covers, it saves a lot of time when trying to make them swarf proof when fitted to your machine.
Measure carefully your machine when giving them the full sweep of your ways, the scales are somewhat longer as there is a safety area built into each end of the scales, so they will be somewhat longer than the strokes of your X&Y.

My Chinese ones have been going for years now without missing a beat. The more accurately you fit them, the longer they will last you and say goodbye to looking at the dials on your machine.

John

 

[bazmak]

I too am looking at digital scales.These look as good as others.Have checked the link
and site is on chinese new year.I have a vernier fitted to the Z axis but
would still go the whole hog and buy 3 axis.Will check it out later and repost

 

[Cogsy]

Al,
I have seen those as well, the size of the scales(width) will be the problem I think. The read out will be about as good as any other.

Cheers
Andrew

In the fine print it says you can choose between 100mm and 1000mm travel in 50 mm increments so you should be able to get the size you need.

 

[Cogsy]

First thing - the scales in the EBay DRO that you're looking at are "magnetic" scales - Not Glass scales as suggested by another forum member.

I'm confused here - the listing itself says the scales are glass and the correct length has to be specified when ordering. Is this incorrect and they're lying in their description?

The other thing is that I've previously had 2 or the 'self-contained' magnetic DRO strips, with the 'read head' operating on a length of cable with button batteries. Both of them were notoriously unreliable and would jump to random numbers or just keep scrolling along even when the axis wasn't moving. I know they were just cheap crud but they've left a bad taste in my mouth for magnetic scales.

 

[Cogsy]

Al,

I wouldn't worry too much about the quality or reliability, most of the ones in your local shops and distributors come from China now.

Thanks for the info John. I'll have to have a hunt around and see what I can find to sell. I've been counting dial turns far too long.

 

[stragenmitsuko]

As an acceptable alternative , how about one of these ?
Google for digimag readout , there are several suppliers .

Not as fancy as a real digital readout , but very affordable .
IIRC I've seen them for 25€ an axis .

Scales can be cut to length with a hacksaw .
And if you buy a long scale , you can use the cut off part in combination with a spare reading head for a quil depth .


Pat

 

[Blogwitch]

I'm confused here - the listing itself says the scales are glass and the correct length has to be specified when ordering. Is this incorrect and they're lying in their description?

Al,

As I stated above, if and when you order, make it VERY CLEAR in your message to them what the READ lengths need to be, NOT the actual physical length of the scale that is needed (they are a fair bit longer than the read length), but add 20 to 30mm or even more if you have the space to give yourself a bit of slack either way when it comes to fitting them.

Glass scales can be shortened fairly easily, but it is a bit fiddly and a bit of machining is required to reshape the outer case for the end caps. I had to shorten my topslide one for it to fit in the available space so that I could get to the handwheel, and it is still working perfectly many years later.

Mag scales are the thing of the future, but at this time are grossly overpriced just because they are easier to fit, if anything, from their method of construction, the prices should be the other way around. Give it a few years and suppliers will have come to their senses and not being so greedy. I haven't searched on the Chinese sites for magnetic as I have no need to, but I am sure that if you did find some, they should be cheaper than homeland suppliers.

John

 

[miglincit]

I recently bought a DRO for my mill from aliexpress.
It comes with 3 glass scales: 2 are used to add up for Z movement (tailstock-movement and tool-post movement) , and one for X; see e.g. here.

2 axis seem to be too less for a mill/lathe -IMHO

Thomas

 

[Cogsy]

As an acceptable alternative , how about one of these ?

These are exactly the type I've had before (I thought these were the magnetic type but evidently they're not). For me they worked OK for a little bit, then started jumping massively and doing all sorts of weird stuff. Maybe they're a different/better brand but mine came from a reputable bricks and mortar tooling supplier local to me (so not ebay) and they were very disappointing. I won't be wasting any more money on them, though they are very easy to mount I must say.

 

[BaronJ]

First thing - the scales in the EBay DRO that you're looking at are "magnetic" scales - Not Glass scales as suggested by another forum member. There is a big advantage to using Magnetic Scales, and that is that you can easily cut the magnetic scales to the length that you require. Glass Scales are unable to be cut, and as a result must be purchased at the specific lengths required.

RoyG

The Ebay advert specifically states that these are glass scales !
Indeed it goes on to tell you that you need to specify the specific lengths that you need and also explanes that the actual scale is 140 mm longer than the measuring length.

Al, glass scales very soon start to give problems if they get any contaminent at all on the glass surface. They need to be well protected from coolant, oil, swarf, including fingerprints.

 

[BaronJ]

I'm confused here - the listing itself says the scales are glass and the correct length has to be specified when ordering. Is this incorrect and they're lying in their description?

The other thing is that I've previously had 2 or the 'self-contained' magnetic DRO strips, with the 'read head' operating on a length of cable with button batteries. Both of them were notoriously unreliable and would jump to random numbers or just keep scrolling along even when the axis wasn't moving. I know they were just cheap crud but they've left a bad taste in my mouth for magnetic scales.

Hi Al,

The magnetic scales are very sensitive to stray electromagnetic interference. Usually from the mill motor and control unit.

I have some of those and cured the issues that you have by screening the cables running to the read head.

This should work for you:-
I got a suitable length of RG8, 1/2" diameter co-axial cable. Carefully slit and remove the outer jacket without damaging the woven tinned copper braid inside. Start at one end and compress the braid so that it bunches up. You will find that it now comes off the inner insulation quite easily. Thread the cables to the readouts through the braid and smooth down. Use a metal clip, I used some copper "P" clips and bent them round the braid, to fasten it to the metal body of the mill near the sensor. Use another to join and clamp the second length of braid for the other sensor. Use tape to hold the two now screened cables together.

This completely cured all the issues with the display that I had.

 

[kadora]

My China DRO jumps even the mill is disconnected from the wall socket.

 

[grapegro]

Hello Cogsy, I bought a 3 axis dro for my small mill from Delos Electrical Science in China through Alibaba. I selected their mini scales, glass, had no trouble fitting them, made up my own covers for them and can only highly recommend them.Full instructions come with the machine, and their offer of help was well to the fore. I considered magnetic tapes but decided on the time proven glass scales. The digital screen is accurate and fully loaded with all the good From memory, it worked out at around Au $350-400. The firm I bought my mill from wanted $1300 odd dollars to supply a magnetic scale. Certain I made the right choice. Norm

 

[Blogwitch]

Kadora,

Are you sure you haven't got the wrong resolution set up on the display head?

Even a fly farting as it goes past will cause jumping of the end digits.

I set mine up to give four figures after the decimal point, and it is rock solid, if I set it to max, 5 figures, then it jumps about. This is on 5um scales, I don't know if it would be any better if you used 1um ones, as that is for use with the higher res scales but you wouldn't be able to use it on most machines because of the vibration.

On my surface grinder, that has a special display head specifically for grinders, that irons out any fluctuations.


John

 

[BaronJ]

Hi Kadora,

A guy that I know had a similar problem, the display would randomly change readings even with the lathe disconnected from the mains supply. It turned out to be radiated interference from the un-grounded flourecent light above the machine. It took a while to find the source because his workshop had no windows and had to have the lighting on to see anything.

 

[ozzie46]

Look at this .$247.50 with free shipping. This is tthe one I got.
https://www.aliexpress.com/item/New-3-Axis-digital-readout-with-linear-scale-100-1020mm-5micron-linear-encoder-complete-dro-kits/32706451568.html?uttaskid=37001&utcontentid=976&utalgorithmid=2&tracelog=rowan&rowan_id1=eclc_en_1_1_en_US_2017-01-23&rowan_msg_id=rcflUTT_37001_%2457c942e9f6b54d3588da27b6c6917e07&ck=in_edm_other

Told them I had a Grizzly G0704 mill/drill and they sent me what I needed.

Ron

 

[Cogsy]

I have some of those and cured the issues that you have by screening the cables running to the read head.

Thanks for the tips, I did some testing and thought you'd solved the issues for me.

I started by removing the read-out from where I had it on the mill head and moved the cable as far as possible from the mill head and the mill light which I thought may also be causing the interference. I then zeroed it at one end of the mill travel and ran end to end 5 times with absolutely zero issues, plus repeatability looked pretty good as well. So I thought the issue must have been interference which would be solved by your shielding suggestions.

However, I replaced the read-out in it's original position, with it's cable close to the light cord and mill head, and again ran the table through it's entire travel several times. To my surprise and consternation I had zero issues . I have been experimenting with using it under actual milling conditions and again it hasn't had any problems. Although this sounds good, I know it had/still has a problem which could reoccur at any time so I just can't trust the damn thing. I might try the shielding and just keep an eye on it for some time and see if it can regain my trust. If it worked it would be a lot nicer than counting turns.

 

[BaronJ]

Hi Cogsy,

I can understand your frustration. It took a lot of playing about to discover what the problems were. Once I had twigged that it was radiated interference, shielding the cables was a no brainer. I also put a 0.1uf 1Kv capacitor directly across the mill motor to knock out interference from the brushes sparking. I don't know about your mill, but I found that there was absolutely no interference suppression at all on the whole machine.

I didn't mention the capacitor across the motor because I had forgotten about it. But if you do this make sure that you turn off the power or otherwise isolate the machine from the mains before opening and removing the motor. My capacitor is inside the motor top cover directly across the brush holders, since it is a permag motor there is no field windings to worry about. Make sure that you insulate not just the wires from the capacitor, but the whole capacitor as well. These ceramic capacitors only have a thin layer of insulation on them and it is easily damaged.

HTH.