electronic or optical revolution counter

Winding a coil? If you're not going too high RPM, there are mechanical counters that you can just flip every time something goes by.. my local Chinese guy charges $6 a piece for them. McMaster et al ought to have something similar, probably at >5x the price. Took a lot of b*ggering around to get it to work when we did it.

You could use a magnet and a reed-switch activated electronic counter- some of them are battery powered (throw it away when the battery runs out!) and about $60 a shot. Or use a reflective opto pickup, but you'll have to get it quite close to the reflective tape on the chuck to get it to work reliably.

Best regards, Spehro Pefhany

Omron, probably via Digi-Key. They have reflective optical sensors with built in signal conditioning for the detection end and simple counter display modules that should be able to accept the input from the optical sensor. The lathe chuck is probably pretty reflective, so a wrap of black friction tape first followed by a piece of reflective tape ought to do. Not sure why you need counts, spring or coil winding perhaps?

YUP - Coil winding (and UN-winding) I guess I could crazy-glue a leather strap on the chuck and then just count the welts on my forehead ! Thanks. Ken

Spehro, Don't think a mechanical would be good enough. I'd be afraid that it wouldn't catch *every* revolution. The reed switch and magnet would probably work (reaction time quick enough) but I'm not sure *which* electronic counter I need. Thanks Ken

Pete, Black tape sounds like a good idea. What do I need to look for concerning resolution, etc? I'm assuming (I know, not a good idea) that these would transmit some sort of a light source themselves and then pick up the reflection on a sensor?? Thanks. Ken

All kinds of them advertized on E-Bay. Work pretty good from 10 inches or so. No good for checking prop speed.

When you said not speed I took it as not "linear" speed. You mean not RPM.

A magnet and a reed switch wired to the + button on a cheap calculator works for low speeds. Just enter 0+1 and let the switch hit the = every time it turns.

Used that for an odometer entering the circumference of the wheel as decimal portion of a mile instead of 1.

The battery powered Red Lion Cubs are pretty tough and reliable:

Depending on speed and what you can conveniently mount for a target, an inductive prox, photosensor, reed switch, or variable reluctance sensor would work to trigger the counter. The variable reluctance sensor doesn't need a power source and could pick up a projection on the spindle or chuck. Downside is the target needs to be moving above some minimum speed to trigger the sensor.

Here's one that Digikey carries:

It's $37 ea. plus shipping from them. Part # RLC03-ND

You just need a contact closure to make it count (internal battery), and it will count at 100Hz, which is pretty fast (thousands of RPM-

6,000 with a 50% duty cycle). You can find them a bit cheaper elsewhere, but Digikey is a fast reliable supplier.

And maybe this guy for the reed pickup:

The capsules are around $1 and molded capsules a bit more, but the above is nice and sealed.

Best regards, Spehro Pefhany

Love it. Dollar store solution if you have a reed capsule and magnet kicking around.

Best regards, Spehro Pefhany

Depending on how high you want to count engage the threading nut and set the pitch to 10 tpi and measure how far the carriage moves.

John

For a one off get a reed switch (an alarm reed would do) and wire it across the "=" button contacts on an old calculator.

Enter +1 to set it up and then subsequent closures will increment the display by 1.

Check it works first because there is the odd calculator around that does not repeat the ast calculation when the "=" is pressed again & again

Woops you beat me too it - just posted the same further up the thread!

I first saw it used in a telescope tracking arrangemnet.

You want a totalizer. Look for Red Lion or Durant. Most of these can be set up with a reed switch as the sensor.

Jon

digital pedometers are cheap. Not sure how fast they can count. Use a magnet/reed switch to replace the swinging weight. Depending on how fast you want to run it, you might be able to stick it on the chuck. Or put something on the chuck or workpiece to slap the pedometer every revolution. Obviously can't go fast that way.

I would guess a bike computer would work too.

Dan

Resolution shouldn't be an issue if you are just counting revolutions, all of the sensors should be plenty fast for counting one reflective spot per rev.

I used an Omron reflective sensor, something like the Digi-Key OR536 (a part I got as a sample some time ago) as a spindle tach sensor on a mini mill. I made a bracket to aim it at the top locknut on the spindle which has a black oxide finish, and put a square of aluminum tape on it which worked well.

There is quite a variety of Omron reflective logic output sensors available over a wide price range. Something like the OR525 would probably be fine if you can mount it, otherwise something like OR580 might be easier to mount. Just match up the output type with the counter module you select. For a counter, something like the RLC2000 from Digi-Key would probably do the job.

Okay ALL and THANKS SO MUCH for all the suggestion and ideas and links. I've decided that probably the best unit for my application will be the Red Lion Cub 3 model counter and I can "drive" it with a simple magnet and reed switch (which I already have). I have ordered one from Digi-Key tonight (although there was a Cub2 on Ebay which looked a little beat up, but probably would have been fine - I would rather have a new unit). Thanks again to ALL who responded with some fantastic ideas (cheap calculator - never would have thought of that one). Ken Sterling

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How many RPM? Electro-mechanical (solenoid driving counter readout from contact closures on a cam-operated switch) is probably fast enough for any speed you are safe using. :-)

If the counter is electronic, and you are using a reed switch actuated by a passing magnet, look for a mercury-wetted reed switch. Otherwise, you will get contact bounce, and the electronic counter can count *every* bounce. :-)

If a mechanical switch (something like a cam-actuated MicroSwitch, take two Dual input NAND gates (7400 TTL at whatever speed and power level you can find. Cross-link the output of one NAND to one input of the other, and vise versa, and use the switch to connect one remaining NAND input to ground in the rest position, and the other to ground in the actuated position. This circuit will latch, so the switch contacts can bounce all they want -- it won't show up on the output (which can be taken from either of the two NAND gate outputs.

If the counter is a solenoid operated Veeder-Root style counter, it won't react quickly enough for the contact bounce to be a problem, so don't worry. :-)

Enjoy, DoN.