Rev counter for a woodworking lathe

I've bought an inexpensive frequency module off Ebay (search on "digital frequency meter" if you're interested - 7). Irritatingly it
comes without any guidance for use but I rigged up an LM555 to give suitable pulses and have got it reading Hz or rpm by changing a jumper.
The lathe is an elderly Wadkins - sturdy CI structure with a low mounted motor and a four block V belt pulley - very similar to many wood turning lathes of 30+ years ago. It has a 3ph motor driven by an inverter.
I'm looking for suggestions on how to get a suitable signal off the pulley block or spindle.
Thanks for any help
Rob
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You could use a magnetic proximity sensor against a bolt head or grub screw in one of the pulleys, presumably you haven't got any gear teeth to detect?
Peter -- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk http://www.oldengine.org/members/diesel http://www.stationary-engine.co.uk http://www.oldengine.co.uk
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Yes - no gear teeth. I did think about the magnet approach but have no idea of the size of magnet required and whether such an object would upset the balance of the shaft. Does anyone have any experience of using a magnetic sensor - am I right in thinking there are direct sensing ICs now?
Rob
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stationary-engine.co.ukhttp://www.oldengine.co.uk
Yes - no gear teeth. I did think about the magnet approach but have no idea of the size of magnet required and whether such an object would upset the balance of the shaft. Does anyone have any experience of using a magnetic sensor - am I right in thinking there are direct sensing ICs now?
Rob
Attach disk with hole (or holes) and a photosensor, or shine light off a bit of reflective tape if balance is a concern. More prone to dust so I'd personally prefer the proximity sensor approach. There are sensors that will give you an open collector directly so you can derive your signal with no further electronics.
AWEM
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wrote:

Out of interest Andrew, do you know if infra red would be better than 'white' light - ie using an IR led and appropriate detector ? And is reflective tape IR capable?
At the moment my feeling is to go the optical way as it does appear that the magnetic sensor route does require some rather close spacing between the magnet and sensor which would be less easy to achieve. I have made the mistake of 'selling' the idea to several other turners and whatever way I use will need to be adaptable.
Many thanks everyone for your comments and ideas.
Rob
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off
Out of interest Andrew, do you know if infra red would be better than 'white' light - ie using an IR led and appropriate detector ? And is reflective tape IR capable?
At the moment my feeling is to go the optical way as it does appear that the magnetic sensor route does require some rather close spacing between the magnet and sensor which would be less easy to achieve. I have made the mistake of 'selling' the idea to several other turners and whatever way I use will need to be adaptable.
Many thanks everyone for your comments and ideas.
Rob
Most of the 'optical' sensors are most sensitive in the i/r anyway. Shiny aluminium foil is what is used for hand held rev counters. Just avoid high ambiant light levels so inside the cabinet.
AWEM
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Rob, I tend to agree with the magnetic senso rroute for robustness against contamination,especially on a wood lathe, but a slotted opto switch like RS Stock No. 304-560A is cheap and easily mounted and pretty resilient. I've used them with either a slotted disc or one with a ring of holes. Because the source and sensor are in one item, alignment is easy and it's not much bigger than a sugar cube so it would be easy to tuck away somewhere.
More slots/holes gives more resolution which you may not need, but you can easily 'read' say 100 holes at 3000RPM, it's only 500Hz which is trivial for electronics.
Richard
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Richard Shute wrote:

If you have any old ball mice lying around they have suitable optical sensor pairs in them, though you will have to make a disc.
-- Peter Fairbrother
I've used them with either a slotted disc or one with a

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On Thu, 8 Apr 2010 01:11:04 -0700 (PDT), Robg

Rob -
I used a Hall effect switch and a small magnet as the sensor for my Myford lathe CNC conversion (written up in MEW) - an A1101 part. You connect pin 1 to +5V, pin 2 to 0V, connect a 10K ohm pull-up resistor between pin 3 and +5, and take the signal from pin 3.
The magnet can be quite small - the "rare earth" magnets are ideal. If you drill a hole in the side of the pulley & insert the magnet with a bit of Epoxy it shouldn't un-balance the shaft significantly. You have to make sure that the North pole of the magnet faces the sensor - it won't respond to the South pole.
Regards, Tony
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See for example:
http://www.hemingwaykits.com/acatalog/Ignition.html
for a suitable kit of parts.
David
--
David Littlewood

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Yes - no gear teeth. I did think about the magnet approach but have no idea of the size of magnet required and whether such an object would upset the balance of the shaft. Does anyone have any experience of using a magnetic sensor - am I right in thinking there are direct sensing ICs now?
Rob
Mag sensors have very short ranges, typically 2 to 0.5 mm, and will pick up any metal "target". its often possible to find an existing "bump" like a bolt head over which you can mount a sensor.
Jonathan
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If you use one of the Sick range, they have one that is M8 body thread and about 2.5" long. 3 connections via a plug with push or threaded fitting.
It has its own magnet built in, and just needs a ferrous object to pass close to trigger.
https://www.mysick.com/eCat.aspx?go=FinderSearch&Cat=Row&At &Cult=English&FamilyID$8&List=1&Category=Produktfinder&SelectionsI69
We use those, might have a spare cable for one, even a secondhand sensor. Peter -- Peter A Forbes Prepair Ltd, Rushden, UK snipped-for-privacy@prepair.co.uk http://www.prepair.co.uk http://www.prepair.eu
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In article

Although not exactly what you want but it may be of interest to others wanting a cheap tachometer for a mill or lathe - what about modifying a cheap cyclometer for a bicycle? eg : http://www.machinistblog.com/?p &18
Alan
--
snipped-for-privacy@argonet.co.uk
snipped-for-privacy@riscos.org
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