Simple RPM meter?

What would be the simplest way to build an RPM meter to measure the rotational speed of another device?

I have a drill press and I'm thinking of changing out the step pulleys used to transmit the power from the motor to the chuck. (I need it to run slower and with more torque)

The current step pulleys have a nice little chart with the approximate RPMs. If I find pulleys to work the way I want, I'll have to figure out the new rotational speeds of the new pulley ratios. I can think of a couple of possible ways to go about it, but was wondering if folks might have suggestions I didn't think of. (I have a lot of shields and parts already and this doesn't need to be a dedicated meter - I just need to read it once, right it down and be done. I don't care if I read it on the larger diameters of the largest step-pull or using something connected into the chuck of the drill press itself, but I do need to measure the chuck speed and not the motor speed)

SW

One way to go is with a magnet and hall sensor.

To mount the magnet in the chuck, I would use a right angle bracket with two holes in it. One hole will take a threaded rod or bolt held in place with nuts on either side and this rod will mount in the chuck. Using the other hole, I would mount an outward facing counter sunk disc magnet (http://www.kjmagnetics.com/products.asp?cat=173).

For the hall effect sensor you could use something like the Hamlin flange mount 55140 or 55100 series. These sensors are activated by the south pole of the magnet, so you want to select the magnetic disc so that the south pole will be facing out towards the sensor.

You can make a wood disk with a bolt through it. Put a small magnet on the edge, make sure it won't come loose. put the bolt in the chuck. Then use a hall effect sensor or a reed switch to read the magnet pulses. Write a sketch to read the time each pulse takes or number of pulses in a given time. That is two ways to do it. There are a lot more ways. Another way paint a white stripe on the chuck and use a photo resistor to read the pulses.

treii28: The current step pulleys have a nice little chart with the approximate RPMs. If I find pulleys to work the way I want, I'll have to figure out the new rotational speeds of the new pulley ratios.

If you just want a new chart to match your new pulleys why not just measure the pulleys and get out your calculator?

...R