Graham

 

Unless I have completely misunderstood your requirement what you are requesting/suggesting would be almost as complicated/expensive as a DRO with scales but have none of the advantages.

 

It would be fairly simple to fit a rotary encoder connected to a digital up/down counter to the leadscrews but it would need an encoder disk with at least twice as many increments as the standard dial just to get the same resolution. By the time backlash has been taken into account what you would end up with would not be very accurate.

 

I doubt you have zero electronic skills! but none would be needed anyway to fit a ready made DRO system. There are some simple ones these days and if you are happy with totally separate displays for each axis why not consider fitting the ‘igaging’ scales (Arc Euro have them). From the description they would need some extra encasing to stop swarf getting in, but for their accuracy they are very cheap, its similar to the very common Chinese calipers so not what you would call traceable standards but they are reasonably repeatable so fine for ME use rather than commercial production.

 

Ian P

 

 

Graham, coincidentally I saw, yesterday, on You Tube something which might be suitable. It was a video of a dividing head in use but with a rod extension on the rotating handle positioned such that it struck a mechanical counter actuator lever once on each revolution. Looked to be ultra-simple in concept and operation. Problem? … can’t remember the location. Will have a search if it sounds as if it might be useful.

Rgds

Bill

 

PS Found it!! 

www.youtube.com/watch?v=Y2QBZQM0d_8

B

You could try here:

 

 

I believe they are intended for angular measurement and they plug directly into their display units, so it might (just) be possible to configure them to display as linear movement.

 

I have the digital dials that John S mentions fitted to my Clarke CL300 lathe and they work OK, but they each get through a battery about every 2-3 months.

 

If all you really need is whole mm’s, then why not get some crisply graduated rules (rulers ) and fit them to each axis and make some adjustable reference pointers to help you keep track of position?

 

Would a conventional DRO work for you, if it were possible to disable some of the digits after the decimal place, because I think that might be possible with some units?

Maybe have a word with the people at the above link if that’s an option.

 

 

 

Martin.

Hi Gray,

For your Emco you would only need an encoder with three (Or a multiple of three.) pulses per revolution. One possibility is the encoders used in mechanical computer mouse. (One that has a ball.) These are very small so they would be easier to fit in the space available. Most mice have optical encoders but one I have just looked at is just contacts on a disk with the encoder pattern as a PCB. I think this type encoder can be bought. They look just like a potentiometer but can rotate continuously. An example of these is This item on Ebay. I should be able to design a display unit to work with these encoders. Would you prefer an LCD or LED display ?

For the unit to display metric or imperial the encoder would need to give more pulses per rev so the truncation of the result of division calculations did not give a significant error.

The normal method to switch between units is to multiply by 125 and divide by 256 for inches and multiply by 127 and divide by 1024 for metric. having the divide part of the calculation as a power of 2 makes the division very easy in binary. (Other similar divisors could be used.)

For the Emco a variation of Cornish Jack’s suggestion but using a tape position counter from an old cassette or open reel tape recorder might work as these counters normally have a zero button. All that would be needed would be gearing up 3:1 from the leadscrew.

 

Les.

Graham.

 

If it is just an excess of numbers on the display that’s the problem, then I can’t help thinking that a conventional 2 axis DRO system with a couple of blobs of BluTack/tape over the offending digits might serve you best in the long run.

 

As a minimum with the modern DRO’s, you get PCD bolt hole and points along a line (at any angle) functions, which should save you some time compared to setting up a rotary table or working out the coordinates for yourself.

 

You probably wouldn’t be able to fix it yourself, should the need ever arise, but I think they’re quite reliable anyway. Good luck with however you do it.

 

 

 

Martin.

 

 

 

Hello Graham,

 

There is a design for a
tachometer using simple, cheap components and an inexpensive Chinese 4
digit LED display in issue MEW 147. Although it is a tachometer, I intend to build for
exactly the same purpose as yourself. The original article uses an
optical sensor (from an old mouse or drive etc) to read a slotted disc. This just needs one slot for recording one rotation of a handwheel or a Hall effect method could be substituted. Here is the
circuit as it appears in MEW 147 in the archive if you have access. If
not I have a copy I could scan and send for your perusal. The power
supply could be based on an old phone etc charger or even a modified computer
PSU. A typical 4 digit frequency meter/counter display with 14mm digits
is here on eBay at £8.70 with free delivery.but there are others at varying prices as is normal.

 

Click on the picture for a larger view.

 

Hi Gray,

The mechanical counter from the video recorder does not have any part number on it. I think it was made for this recorder.

I have tried one of the switch type quadrature encoders from the old computer mouse with the counter that I used with the quadrature encoder on my mill many years ago. To get it to work reliably I had to first clean the contacts and then filter the inputs to the counter with 100 nf capacitors. I found this encoder gave 36 pulses per rev.

Les.

Hi Michael,

This is the only mouse I have seen using this type of encoder. It is probably one of the original serial mice which came before the PS2 mice. (I have cut the cable off so I can’t be sure.)

 

Hi Gray,

I think these modern optical mice work by recognising patterns on the surface of the mouse mat and working out how far it has moved in its field of view as the mouse is moved. These mice would be no good for your purpose. Let me know if you would like either the tape counter or the encoders from the mouse. Although the counter could probably be made to work I think it would be better to use an item that could be obtained again. Farnell have a range of these switch type encoders but I think an optical unit would be better. As you only need three quadrature cycles per rev it should be possible to make one yourself. It could probably even be made using reflective type sensors such as the SY-CR102 from Maplin. I also have a program that will print out the pattern to make encoder disks. Let me know if you would like a copy of that. One way to try to make a simple sensor would be to use some hex bar and paint three faces black and three faces white and use this with the reflective sensors.The sensors would need to be spaced 30 degrees apart. (Or 90, 150, 210 etc)

One other thing you need to consider is when the original scale on the leadscrew is at its zero position you will not be quite sure if the digital display hasjust incremented or is just about to increment. Having the least significant digit displaying zero or 0.5 would solve that problem.

 

Les

 

 

Electronic , electromechanical and pure mechanical counters off the shelf .

 

Very long established business – made the original Veeder counting devices for odometers and early calculators – and they still do .

 

MW