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 !!!
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