Cross Slide Rotary Encoder

[John HaineParticipant @johnhaine32865]

The encoders that Joe referenced look nice, but would one need to calibrate them? For example, the LS pitch might be a bit off, or the screw somewhat worn.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by YouraT on 17/10/2022 17:10:21:

Not me, although that names are similar

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Oops ! … I thought it was an a.k.a.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 17/10/2022 17:12:30:

The encoders that Joe referenced look nice, but would one need to calibrate them? For example, the LS pitch might be a bit off, or the screw somewhat worn.

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Ultimately, direct reading of linear movement must be the preferred option, but if Speedy just wants a convenient display of Metric values this seems very expedient, and almost certainly better than the visual resolution of a Boxford dial.

MichaelG.

[duncan webster 1Participant @duncanwebster1]

Way back in the mists of time (2013?) I described in ME how I'd mounted an encoder onto the leadscrew of a Cowells lathe. Readout by Arduino. It had a 90 slot wheel which gives better than half a thou resolution with a 0.1" pitch screw. You'd need to find a way of mounting the optoswitches onto the handwheel bracket. By this time, I'd be seriously looking at just buying the gubbins and using a magnetic tape. You'll want DRO on the saddle soon enough having got used to it on the cross slide. If you want a copy of the article send me a pm

[Mike PooleParticipant @mikepoole82104]

Chronos list these displays for the C3 type lathes. You may be stuck with the feedscrew pitch of the C3 lathe though.**LINK**

Mike

[Speedy Builder5Participant @speedybuilder5]

I guess I was looking for something like this with a hole through the middle?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Speedy Builder5 on 17/10/2022 19:31:53:

I guess I was looking for something like this with a hole through the middle?

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That was certainly my assumption

… and what Mike links 

MichaelG.

Edited By Michael Gilligan on 17/10/2022 19:50:40

[JasonBModerator @jasonb]

They do have a hole through the middle see here

However as I said in my first post I think they come set up for metric screws so one turn will read 2.00mm or 0.079" on the display

[AJAXParticipant @ajax]

Why not just fix a dial indicator to the cross slide to show movement across the bed? Cheap, no battery, easy to read and zero.

[Speedy Builder5Participant @speedybuilder5]

Fair point Ajax! The CHRONOS readout is the sort of thing I was looking for, like Jason said, if I could change the pitch of the feed screw on the device.

Bob

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Speedy Builder5 on 18/10/2022 06:48:07:

[…] like Jason said, if I could change the pitch of the feed screw on the device.

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That’s why I said this style of read-out had disappeared by ‘natural selection’ [Darwinism]

I have never looked inside the SIEG device, but I suspect it is very similar to the WolfCraft one.

That simply didn’t have enough ‘native resolution’ to cope as a data-source for Imperial/Metric conversion.

Sorry, I no longer have the device, so I can’t take photos … but it was mechanically quite crude.

MichaelG.

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Edit: __ See here for the use of Gray Code on shafts:

 https://en.wikipedia.org/wiki/Gray_code#Position_encoders

If I recall correctly the WolfCraft device only used four tracks

[as per the monochrome illustration on that page]

Edited By Michael Gilligan on 18/10/2022 07:54:48

[Michael GilliganParticipant @michaelgilligan61133]

This [being a more sophisticated SIEG unit] is interesting: **LINK**

http://www.mini-lathe.com/mini_lathe/reviews/Sieg_DRO/dro2.htm

MichaelG.

Edited By Michael Gilligan on 18/10/2022 08:10:25

[JasonBModerator @jasonb]

Thanks for the last link Michael, I knew they were thread specific but thought it was the metric thread.

What's really needed is something like a bike computer where you set distance according to tyre diameter but in this case it would be thread pitch. Switching between radius and diameter reading would be an added bonus.

[Michael GilliganParticipant @michaelgilligan61133]

Just spotted this offering by ARC : **LINK**

https://www.arceurotrade.co.uk/Catalogue/Machine-Spares/SC3-Mini-Lathe-Spares/SIEG-Mini-Lathe-DRCD-to-Manual-Conversion-Kit

It would be interesting to know what has driven this

MichaelG.

[JasonBModerator @jasonb]

That will be the same one I linked to about this time yesterday

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 18/10/2022 10:05:05:

That will be the same one I linked to about this time yesterday

.

Apologies, Jason … I don’t recollect following your link [because I wrongly assumed it would be for a ‘digital upgrade’ not for an upgrade from digital to mechanical]

mea culpa

MichaelG.

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P.S. __ I now also note that the SIEG digital unit, that it is shown as replacing, is already the more sophisticated version [!]

Edited By Michael Gilligan on 18/10/2022 10:32:26

[JasonBModerator @jasonb]

A little birdie tells me they use a disc that is encoded for a specific thread pitch.

Prone to problems with cold temperatures as well as ingress of swarf and coolant that caused unacceptable number of failures, new version thought to be equally as prone to problems.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks

[Speedy Builder5Participant @speedybuilder5]

Finally got there. Using an Arduino and Encoder, a couple of in line flexible joints and now can read out to 0.0001". A bit of a tight squeeze into the aluminium box and at first noise between the encoder cable and general electrical noise. We seem to have a stable and repeatable system by Screening the Encoder cable attached to the metal box and encoder "grounded" to the lathe.

The switches are On/Off  Reset  and choose of Radius or Diameter setting (Not sure if I would ever need Diameter !!)

Edited By Speedy Builder5 on 25/11/2022 16:46:06

[Ian PParticipant @ianp]

Posted by Speedy Builder5 on 25/11/2022 16:44:09:

Finally got there. Using an Arduino and Encoder, a couple of in line flexible joints and now can read out to 0.0001". A bit of a tight squeeze into the aluminium box and at first noise between the encoder cable and general electrical noise. We seem to have a stable and repeatable system by Screening the Encoder cable attached to the metal box and encoder "grounded" to the lathe.

The switches are On/Off Reset and choose of Radius or Diameter setting (Not sure if I would ever need Diameter !!)

Edited By Speedy Builder5 on 25/11/2022 16:46:06

Look like a couple of 'out of line' inline couplings!

Ian P

[bernard towersParticipant @bernardtowers37738]

So if your couplings are out of line how can your measurements be ok to .0001 at all points of rotation?. Wouldn't it be better if the encoder was directly in line with the feed screw ?.

[SillyOldDufferModerator @sillyoldduffer]

I like it except the measurement is of screw turns rather than tool movement and is thus vulnerable to backlash error.

The Arduino could be programmed to compensate but would need to be recalibrated periodically as the nut and screw wear. Which reminds me, the amount of backlash on my lathe has crept up enough to annoy me again. There is no rest for the wicked…

Dave

[Les RileyParticipant @lesriley75593]

I had been meaning to fit some sort of reader to my Myford for many years. However, as above, I didn't want a bulky slide in the way.

At the Midland Exhibition in 2019, I saw the DRO stand with the magnetic strip fitted under the cross slide. Perfect.

Completely hidden and no backlash problem. All the old lash-ups devised over the years are history.

[Speedy Builder5Participant @speedybuilder5]

I don't know where my reply went to Bernard, but the reason for the offset is that the cross slide would foul the encoder as it reaches full travel. I had a quick scout around to see what the angular error might be, but didn't find anything on the net.

Dave, I could live with that probably no worse than the divisions on the cross slide handle Its been an interesting exercise in rattling the grey cells.

Bob

[Ian PParticipant @ianp]

Without dimensions or knowing what lathe this is it is hard to offer an opinion or make judgement on the arrangement, however from the picture it looks as if the cross slide will be well out of its dovetail engagement by the time it gets anywhere near the encoder body diameter.

At full travel does the cross slide pass over the encoder?

To minimise angular accereration errors in (pairs of) Hooke (and I presume beam type) couplings, the input and output shafts need to be parallel but also the 'phasing' of the two couplings has to be correct. On a Hooke joint the pivot points are obvious but on the helical coupling it would be a bit more difficult to define just where the beam starts.

Ian P

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