Looking for links for a fairly good, reliable and accurate revolution
(not speed) counter to attach or use on my metal lathe chuck.
Reflective tape on the chuck or (less desirable) a magnet on the
chuck. I've been looking, but I'm not finding what I think will work.
Anybody using something on their lathe that works good? Any good
ideas? Help greatly appreciated.
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.
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
Not sure why you need counts, spring or coil winding perhaps?
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.
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??
When you said not speed I took it as not "linear" speed. You mean
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.
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.
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
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.
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
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).
[ ... ]
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. :-)