DRO scales

[DalboyParticipant @dalboy]

I am thinking of adding a DRO to my lathe, There are different types of scales which are the best type.

I don’t want to set this up with something that costs an arm and leg, but at the same time something that is not cheap and cheerful.

Also, which 2 axis control panel would people recommend

[Robert Atkinson 2Participant @robertatkinson2]

What size lathe?

 

[bernard towersParticipant @bernardtowers37738]

Ive set my S7 up with magnetic scales and control panel from M DRO and touch wood they have been faultless (should i have said that). The crosslide scale is buried inside. Has now been running for several years.

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

What size lathe?

 

I am sorry Robert but how does that help in recommendations for type of scales as I already know the sizes needed.

[Robert Atkinson 2Participant @robertatkinson2]

It makes a difference because small lathes don’t have so much space for scales and read heads. Different technogies can be different sizes. A larger machine is also more likely to accept over length scales without them getting in the way. You can’t cut some scales easily.

Robert.

[SillyOldDufferModerator @sillyoldduffer]

Pleased to see Roberts answer about size matches the thought process I went through selecting a DRO for my mill.

I prioritised inexpensive and easy to fit over features and best possible accuracy.  Capacitive tracks are easily cut and take up less space than other types, plus they are at the cheapo end.   I didn’t expect them to last, yet they’re still OK after 10 years.  Still available from Arc Euro, very basic, and they transformed my mill.

If money is no object, and you don’t mind a fitting challenge go magnetic.  Cheaper these days, but still pricey.

Glass was cheaper than magnetic, with several other advantages compared with capacitive scales, but harder to fit. For my purposes glass is more than ‘good enough’.

Rough rule of thumb, though much depends on your machine’s geometry, it’s easier to fit scales to bigger machines simply because they have more space.

Ten years ago there were a lot of incompatible proprietary scales and displays about.  So there was advantage in buying scales and display together as sets.  Probably less of an issue today because standardisation has had time to bite.  Nonetheless, if mixing and matching scales and display heads from different sources, I’d check their specifications to be sure they will talk to each other.  Just in case!

Dave

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

It makes a difference because small lathes don’t have so much space for scales and read heads. Different technogies can be different sizes. A larger machine is also more likely to accept over length scales without them getting in the way. You can’t cut some scales easily.

Robert.

OK understand now. The lathe is a WM280v and requires a 200mm and 600mm scale

[PeteParticipant @pete41194]

I can’t comment about the cheaper off shore dro’s and scale types simply because I don’t know how good they are. My Newall can use and allows two levels of the magnetic scales and reader heads. Spherosyn scales with a 10 micron accuracy, and Microsyn with a 5 micron accuracy level. Glass or the non magnetic scales and reader heads can usually allow higher accuracy levels than that. The trade off is there much more easily and permanently damaged by scratches in the glass or contamination affecting the readings. But for what most of us might be doing, you first have to ask if you and the machines you own are capable of using or machining to even that level of accuracy. If it were me, I’d first check what the stated level of accuracy is for the dro and scale type your thinking of purchasing.

There’s also a few terms you first need to properly understand about any metrology equipment. And there not interchangeable and certainly don’t mean the same thing.

Resolution, in simple terms and all that amounts to is how many digits there are to the right of the decimal point. And that is NOT nor should it ever be confused with just how accurate any piece of metrology equipment happens to be.

Repeatability, again in simple terms it means how well the system or tool repeats the same measurement each time. It’s roughly a factor of the care and quality of the individual components used and assembled to produce that expected level of repeatability.

Accuracy, it’s also a factor of that same assembly process and that component quality. The usual world wide standard most manufacturers adhere to is the system or measurement tool has to repeat and be accurate to + – one count. Or + – 1 division of the smallest number it’s capable of displaying in analog or digital form. However, at these levels of repeatability and accuracy, most of us would find it very difficult to actually check that what were buying is in fact as repeatable and accurate and does perform how any manufacturer claims it will. So there is some possibility for let’s call it cheating by less than reputable manufacturers should they decide to do so.

Maybe a bit outside what most of us require, but I think still worth understanding.With any dro including the very best, how those scales and reader heads are mounted and the environment there exposed to such as temperature variations can have a direct effect on the systems ultimate level of accuracy and repeatability. My Newall is set up to allow what’s called mapping of the scales travels against what the display unit shows as the measurement. Due to various factors, there may be slight differences that can affect it’s real world performance and accuracy. So that built in function allows using very high accuracy gauge blocks or even laser interferometry to then calibrate the dro to the actual slide movement verses what the display might be showing. But I suspect that option is mostly intended for surface grinding equipment. I’m fairly sure some of those newer off shore dro’s also have that available today. And from various posts I’ve read elsewhere, I’d certainly be willing to spend a bit more just to get a dro that has a proper and well explained user manual. Price isn’t the only criteria in my opinion.

Most lathe specific dro’s today will usually allow displayed pre sets for each numbered, pre checked and calibrated tools zero point to the work piece. It’s more useful I think when producing multiple parts of the same dimension. And to get the most out of that option, the quick change tool post and tool holders need to be a trusted brand name and have an industrial level of quality and with extremely good built in repeatability. The much cheaper off shore QCTP and holders can’t nor were they ever intended to do that.

[Wink HackmanParticipant @winkhackman25989]

I second Bernard’s recommendation of the magnetic scales and readout from M-DRO.  They’re compact and come with a good fitting kit and instructions.  Telephone support too.

[Clive FosterParticipant @clivefoster55965]

Objectively there is little doubt that an internally mounted magnetic scale is the best approach for the cross slide on a smaller lathe. Such as this one. Unfortunately that is the hardest way to mount things because it commits you to engineering your own mounts and, possibly machining the slide or saddle castings

Externally mounted glass scales generally take up space of the order of 1″ – 25 mm square alongside the cross slide and magnetic ones maybe half that. The read head is a significant block but generally that can be gotten out of the ay to the real. Normal practice is to put an external scale on the tailstock side which limits how close the tailstock can get to the saddle. Effectively restricting the amount of useful travel in some situations.

You only have 2 3/4″ – 70 mm of tailstock travel which I would regard as barely sufficient. Particularly if you use a quick change toolpost and need to work right up to a centre.

Inadequate tailstock travel was the final thing that drove me to swop from a SouthBend Heavy 10 to my Smart and Brown 1024. Going from 2 1/2″ to 4″ travel was immensely liberating. If you decide to go for scale mounted on the tailstock side of the cross slide I suggest that you do a mock up with a square piece of wood for the seal with a block on the end to represent the read head and verify that neither interfere with the work you do. Just because I’d find the tailstock restrictions intolerable doesn’t mean that you will have issues. But best to check.

Chuck side mounting of a scale is generally frowned upon because of the obvious swarf issue as it’s on the working side. It also can get in the way with collet and faceplate work. But folk have made it work well enough for them.

Longitudinal scales are generally mounted behind the bed. There is rarely any issue with clearances or space although a little creativity may be needed if you have taper turning unit. Personally i’d go for glass at the back as generally being little cheaper than magnetic. Magnetic scales are allegedly a bit vulnerable to very fine swarf under some circumstances in long term use. But I doubt if  Model Engineering work would put enough hours on the scale for that to ever be problem.

Often the rear of a lathe bed doesn’t have any nice flat surfaces to make mounting easy. If there is nothing suitable an effective way of creating a pair of aligned, decently flat surfaces is to apply car body filler in the appropriate places then push a carefully aligned, greased L section bar against the filler and leave to set. The greased bar will come away leaving a nice flat surface on the filler. I used 2″ x 2″ x 1/4″ right angle alloy extrusion when I fitted scales to my Bridgeport approaching 20 years ago and it worked a treat. Establishing accurate alignment before applying the filler did require some patience and verbal encouragement.

Before final purchase of the display unit it’s prudent to download the manuals for candidate systems to verify that you will be happy using it. Although all are operated in generally the same way its quite possible that you like the way one make works whilst another has that one thing that will drive you nuts.

These days there seems to be little difference in performance and reliability between recognised brands. I’d be chary of the uber cheap variety. Whether direct from China or via a non technical middle man. It seems wise to have someone technically knowledgeable to go back to if there is problem. The price premium for industrial units such as Newall, Accurite et al can’t be justified in the home shop.

Clive

[JasonBModerator @jasonb]

I’ve glass scales and console from Machine DRO on my mill and no problems after 15yrs. Magnetic was not really an option then

If I decide I need a DRO on my 280 I would go with magnetic from the same supplier.

The main issue is the cross slide, fit it to the right hand side and you loose access to teh cariage lock and the tailstock can’t get as close so excessive overhangs. Put it on the left and it means more tool stick out when machining large diametes, right wher all the muck is etc This applies to glass and to a slightly lesser degree magnetic once the covers are on.

There is not too much modification needed to fit a magnetic strip under the cross slide and a small rear extension can take a mini read head. There is a thread on the subject here somewhere and that is the way I would go to avoid all the problems mentioned above.

May also put a third one on the topslide and have a consol that does summing so whether you move the carriage or the topslide when set parallel the single line on teh consol gives tool position.

I would also fit longer than 600mm, there have been times when I have been turning long work supported by a fixed steady with the carriage right to the end of the bed with the tailstock removed which would not be possible with a 600mm scale fitted.

[Pete]

On Pete Said:

… But for what most of us might be doing, you first have to ask if you and the machines you own are capable of using or machining to even that level of accuracy…

This is an important point!  The capacitive scales I fitted to my mill 10 years ago use the same technology as a digital caliper, and are accurate to about ±0.02mm (about a thou).    Never tried to measure how accurate my mill is, because that’s hard work, but it’s a shade better than ±0.02mm.   It’s a WM18 not a Jig Borer!  On a good day, with the screws clean, gibs spot on, sharp cutter at the correct speed and feed, work bolted down properly, and me driving carefully, not trusting the DRO, I can get ±0.01mm out of it at least over short distances.

My mill’s limitations suggest fitting a 1 micron scale (0.001mm / 0.000039″) is a waste of money because the machine can’t match the scale’s accuracy.   A sooper-dooper scale cannot improve the accuracy of my work.   On my mill a 5 micron scale (0.005 / 0.0002″) is more sensible, because 0.005mm is good enough to detect what the machine is doing within it’s capacity – approx ±0.01mm.   When the ArcEuro scales do the decent thing and die, I will upgrade to 5 micron and a single display head.

Same applies to lathes.  Mine is a WM280V, for those not familiar, it’s a Chinese Hobby machine somewhat larger than a Myford 7, but not massive.  A big example of a small lathe!  Like my mill, it comfortably works to ±0.02mm, suggesting a 5 micron scale is appropriate.  It is not a tool-room lathe.

Unless his machines are worn, Pete’s workshop equipment is a notch better than mine.  That clearly nudges him away from cheap capacitive scales, and although 5 micron would probably be ‘good enough’, he might well get value out of 1 micron scales.

Is a DRO necessary for accuracy at all?  Or is extreme accuracy itself necessary? Rarely in my workshop.

Whilst DROs and Digital Calipers are a huge convenience and time-saver, I mostly work by fitting.  I do not bore a hole ⌀20mm ±0.02  and then turn a shaft ⌀19.90mm ±0.01 so the two will go together without further ado!  More likely I will bore the hole to about ⌀20mm, and then turn the shaft to a little over that.   Then, using the hole as a gauge, I shave down the shaft step-by-step until it achieves the required fit.    There is no need to measure anything accurately.  Usually shave down with a single point tool and then finish with emery paper.  Emery paper removes tiny amounts of metal, allowing even crude machine tools to achieve high-accuracy / close fits when needed.

Experimenting with old-school techniques is interesting if there’s nothing urgent on hand.  Although it takes longer, and the resulting parts aren’t interchangeable, fitting with nothing more than a plain spring caliper works surprisingly well without measuring. Better made versions available:

I’ve found answers to Dalboy’s topic most useful.  Things have moved on since I fitted a DRO 10 years ago, in particular magnetic scales are now an affordable option.   As we have the same lathe, if Dalboy reports what he installs, I might well copy him!

Dave

 

[Michael GilliganParticipant @michaelgilligan61133]

Further to Dave’s helpful analysis

… I have just dug-out an important name from my bookmarks

Hans Ulrich Meyer

‘Who He ?’ you might ask … Well, he basically invented the “Chinese” capacitative scale

https://worldwide.espacenet.com/patent/search?q=%22meyer%20hans%20ulrich%22

 

MichaelG.

 

[DiogenesParticipant @diogenes]

If you want ‘full functionality’/all the features, then it’s ‘what Jason said’.. ..3-axis..

If you just want to know where the toolpoint is in X & Z, a two axis will be okay, you might get some ‘extra’ features( i.e. taper/radius), but certainly on the cheaper units they might be clunky and hard to figure/use.

I have a glass scale on the ‘chuck-side’ – you can’t get too close to the faceplate, but ‘reach’ issues aren’t as bad as you might think – not bad enough to compromise use of the tailstock, for my preference. Pic below with normal tool, second pic with boring bar.

Machine is a 280-swing GH600.

The three-jaw passes over the scale with he jaws hanging (right) out.

I don’t have problem reaching the ‘backplate collet chuck’ I use.

[DalboyParticipant @dalboy]

Thank you all a lot to think about. The wife is the guilty party, as she asked what I would like for Christmas. It was this or a power feed for the mill.

[Harry WilkesParticipant @harrywilkes58467]

Choose the DRO and then for your birthday a  power feed for the mill …..

H

[bernard towersParticipant @bernardtowers37738]

Its got to. be the DRO then!

[Dalboy]

On Dalboy Said:

Thank you all a lot to think about. The wife is the guilty party, as she asked what I would like for Christmas. It was this or a power feed for the mill.

Oeer! I’m conflicted about that choice.  I’m not convinced that DRO on a lathe is high value.  It’s because most of the cuts I take whilst turning are short distance, and it’s not difficult to compensate for lathe backlash.   In contrast, mill cutting is often long distance, backlash hazardous, and counting dial turns is error prone.   DRO on a mill is wonderful,  DRO on a lathe not so much.  Not got DRO on my lathe, and don’t miss it, but what do DRO owners think?  I could be missing something.

Long distance on a mill is tedious because of all the handle cranking needed.  And manual handle cranking is liable to produce a poor finish due to a jerky operator.  As power feed helps both problems it would be my x-mas pressy of choice.   Easier to fit as well!

Dave

[Harry Wilkes]

On Harry Wilkes Said:

Choose the DRO and then for your birthday a  power feed for the mill …..

H

Birthday present already brought a little early as not till next month. A nice little roll along draw unit for storage.

The WM18 mill has a long bed, so choice is hard

[PeteParticipant @pete41194]

As far as a dro on a lathe and it’s usefulness.

It depends on what the usual project type might be for any of us. M.E. or even having machine tools of any type isn’t always or only about building engines, locos etc. There’s also ways and maybe an individuals own requirements to get more use out of a lathe dro. That very good QCTP and pre zeroed tools I mentioned as one example. Having a lathe that’s fairly rigid, large enough to even mount a dro, the lathe installed, leveled and properly tested that it can produce parallel parts over longer distances. Plus the rest of the lathes 3 dimensional geometry or amount of wear already present is also important to what a dro would add to any lathe.

For a mill, it’s one of the best accessories I’ve bought, and it took far more time, thought and effort to install, align and get fully operational than any lathe would. I’d like to have the same on my own lathe at some point, but for myself, it’s a bit less important right now. A simple and even fairly cheap dial indicator and maybe a few micrometer checking rods that most of us already have can still duplicate a lot of what a dro can do, it’s just not as convenient and of course much slower. Multiple millions of parts used to help win WW II were produced without a single dro even being available. But if a lathe dro is what anyone wants and can afford to do so, then that I think should be a good enough reason.

 

[JasonBModerator @jasonb]

I wa sinterested in Dave’s comment that a DRO has little value to him as he “mostly turns short distances”

If I were to fit a DRO to my lathe that is one of teh reasons I would want it to keep track of short distances. Things like cutting a series of fins in a cylinder or using co-ordinates to rough out a curved shape. Lots of small lengths that add up and if you are not careful errors can creap in or you can simply loose count of teh handwheel.

This sort of work

[Stuart Smith 5Participant @stuartsmith5]

My Warco WM290 came with a DRO fitted. The screen has 3 inputs but only 2 scales were fitted. I fitted a 3rd scale to the top slide. As Jason said earlier, if you do this you can get the display to sum the 2 readings together. I find it useful. Some photos attached.

[duncan webster 1Participant @duncanwebster1]

If I could only have one I’d fit DRO to milling machine, but having got one on the lathe I wouldn’t be without it. Hardly ever look at the dials.

[JasonB]

On JasonB Said:

I wa sinterested in Dave’s comment that a DRO has little value to him as he “mostly turns short distances”

If I were to fit a DRO to my lathe that is one of teh reasons I would want it to keep track of short distances. Things like cutting a series of fins in a cylinder or using co-ordinates to rough out a curved shape. Lots of small lengths that add up and if you are not careful errors can creap in or you can simply loose count of teh handwheel.

This sort of work

 

Good point!  I rarely cut fins or curves.   I would have to take extreme care making something like Jason’s cylinder head especially if the part had to look good when finished.   No doubt a DRO is helpful for complicated objects,  but my requirements are straightforward.   For example, I don’t think a DRO would speed up the machining needed to make a PottyMill?

Dave

[duncan webster 1Participant @duncanwebster1]

You’d be surprised. Saves an awful lot of mental arithmetic, and unless you’re working to small limits, saves a lot of measuring.

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