Made from an inexpensive digital tyre depth gauge available on eBay this portable DRO shown in position to measure the travel of the cross slide on a mini lathe.
The Mk lll mini DRO is an evolution of a brilliant idea from Rob in Australia. Up to now setting up a digital read out system has been an expensive and labour intensive undertaking with questionable reliability. This little gizmo can be put together in around one hour at a cost of less than £10. It snaps into position thanks to the powerful rare earth magnets (neodymium) when required and can be removed just as easily.
I regard this DRO as ideal for use on the lathe to accurately measure travel of the cross slide and carriage. We can all get within a few millimetres when turning or boring but its that last few mm or thousands of an inch that gives us either the ‘spot on’ size we are looking for or relegates the workpiece to the scrap bin. No doubt with imagination this unit can be used equally effectively on the mill.
In Mk l and Mk ll versions a spring was an important element in the operation of this little unit. However in an Eureka moment my friend, also from down under, Aussie Jim, suggested scrapping the spring and using a small magnet on the tip of the probe.
Brilliant ! The following is a step by step guide to making your own DRO unit.
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- For around £5 buy yourself a digital tread depth tyre gauge, there are loads of them on eBay.
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- Remove the sticky label off the back and clean up residue with a solvent like brake cleaner.
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- Remove the CP2032 button cell and remember to buy a couple of spares at the next autojumble.
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- Take apart and relieve the pressure of the strip metal tension spring by straightening.
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- Turn up a 3mm dia steel sleeve (not stainless) to slip over probe and take two 3 x 1.5mm rare earth magnets.
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- The sleeve and the magnets are held in position with a dab of Araldite. Note the magnet protrudes slightly from the sleeve.
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- A 2mm thick 1″ square steel plate is recessed to take four 9 x 1.5mm rare earth magnets.
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- The DRO in position to measure the travel of the cross slide.
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- Mk l with external spring, Mk ll with internal spring and Mk lll with no spring at all !!!
Thanks. Have got a proper hand-wheel/dial from Myford. goimg to use nail varnish for colour coding.
Re the DRO; my idea,that I am going to try out on my little Emco Unimat-4, is to position it opposite the tool-tip; slide it in to touch the work, zero it; slid it in to give the actual, full oversize figure, and then simply cut away till zero readout. Hence my name for it = ZeRO or 0RO.
Just going to bend up a bit of steel bar from B&Q in Z-shape and fix to rear T-slot on Myford cross slide, to set to centre height.
Any ideas/comments please?
Good news on your handwheel and I like your idea of using nail varnish for colour coding.
Your planned use of the DRO sounds good to me. There are clearly a variety of ways in which the DRO can be used which will vary according to circumstance. Whichever method you employ it does make machining to fine tolerances so much easier than having to constantly stop the lathe, measure, take another cut, etc.etc.
John
Thanks for yor welcome. Remember, at that time a sslary of £75/month was far beyond most folks hopes!
Like the look of your DRO and will try to make one. Can’t quite see where yours is mounted in the photo? I assume it is in line with the tool-tip? If so one would have to measure the over-size dia, halve it,and then note the answer and work to that; is this so?
My first thought (please remember I am the new ‘kid’on the block) is that if you set it on the far side of the work-piece, afew microns down streem from the cut,and then position it so that the required dia reduction is reading, you then only have to work DOWN to zero.
May call mine a 0RO or ZeRO instead of DRO?
Apologies if all that is a load of …..
Oh, please do you know where I can get some decent hand wheels, with readable, clear scales, for nmy bross,top and vertcal slides? Now have to colour code them, black=0, red= 50, yellow=25 and blue=75, as my one remaining eye is not too clever at details.
Photos to follow.
JMcK.
Sorry for the delay in replying. Your assumptions on calculating the distances are correct. I usually measure the width of the workpiece, deduct the required finished diameter and divide by two. I then use the resulting figure for the amount of travel. Depending on your lathe setup mount your DRO in a convenient position on the cross slide so the travel can be monitored.
Replacement handles are available from the main tooling suppliers (see my Resourcses page) but I think you would have to devise your own method of marking which admittedly requires a dividing head. It’s not something I have done so am unable to advise you further.
John
What a find !
A most super-useful site.
Have added to my “Direct Entry” file system
Am sure will visit many times.
Getting down to some serious machining on my old ML7, that I bought, complete with chucks (3 % 4 jaw + 1/2″ drill) plus odds & sods for about £75! about 60+ years ago.
Regrds, John.
Glad you found us and that the site is useful to you.
ML7 with all the bits for £75 ? we spend more than that on groceries each week. have fun John and remember I love to receive pictures and workshop tips.
John
Hi John on the dro i see you recessed the 2mm base plate how deep was this? and why did you think it necessary. A great site and a good help. Many thanks Colin.
Hi Colin
I recessed the magnets to prevent the magnets leaping towards each other whilst the retaining rapid araldite cured.
Depth of recess not critical 0.5 to 1 mm at a guess !
John
Hi John,
Thank you for your comments and is certainly a solution
Maybe another way is to use the digital for the rough stuff and the dial for final cut.
Regards
frank
Hi
What a great idea, I think that there is a bit of a problem with the linearity of the digital gauge.Checking against the dial on my Colchester Bantam. Here is a sample of the readings
0-0, 10-0.5, 20-0.97, 30-1.44, 50-2.4, 60-2.9,70-3.4,80-3.92, 90-4.44,100-4.98
Mid way there is a difference of 0.1. I suspect that the error is in the digital gauge rather than the screw. Does anyone have any ideas or where I can get a digital gauge that has proven reliable. It is very difficult to independanlly measure accuratly the movement of the cross slide.
Thank You.
Hi Frank
An interesting observation. Reminds me of the time a few years back when (almost by accident) I discovered to my alarm slight differences in read outs on my assortment of digital scales. Clearly this is not a desirable state of affairs but to achieve a higher level of accuracy could be both costly and too demanding for the home workshop operator.
My way round this problem is normally to use the same digital scale, where critical, throughout a build project which will provide an acceptable degree of accuracy and fit between components. This in my view provides a sufficient level of accuracy for most of the work undertaken by individuals making a start in model engineering.
There are digital scales available for fitment to lathes and milling machines but the cost of such refinement is probably more than the cost of the machines to which they are to be fitted.
John