Motor shaft sizes - do standard sizes exist?

Just starting out using a few DC motors, and some servos, stepper motors etc., and I was wondering if there is any standard sizes for the motor shafts so that standard size gears/pulleys etc can be purchased off the shelf to fit.

For example, I have 3 very nice 12VDC Pittman motors from an old computer data storage device. Their shafts measure about 4.1 or 4.2mm. Am I going to be able to find any pulleys/gears, etc to fit them?

Related question, how do you couple mechanics to your motors usually - a flexible coupling, belt/pulley drive, direct? Do you make them yourself? I had a suggestion from a guy who sells Lego gears and stuff, that people often use a piece of tubing, such as used for air hose in the aquarium trade.

Those Pitman motors are probably 1/8inch.

There are standard motor shaft sizes, There problem is, there are many standards... Metric sizes will probably be either a whole or half millimeter and under 1/8 inch they will probably be in 1/32 inch increments (or 1/64) over 1/8 they will generally go by 1/8ths with a couple 1/6ths thrown in (we seem to like 7/16 and 9/16)

kf2qd: Those Pitman motors are probably 1/8inch.

There are standard motor shaft sizes, There problem is, there are many standards... Metric sizes will probably be either a whole or half millimeter and under 1/8 inch they will probably be in 1/32 inch increments (or 1/64) over 1/8 they will generally go by 1/8ths with a couple 1/6ths thrown in (we seem to like 7/16 and 9/16)

Ah, sounds messy :) . Sounds like you just have to adapt where you can't get the exact right size. Thanks for the help.

You can get gears/pulleys for a smaller shaft and drill/ream them out. 4.1mm sounds unlikely - micrometer or calliper guage is the way to measure.

MarkT: You can get gears/pulleys for a smaller shaft and drill/ream them out. 4.1mm sounds unlikely - micrometer or calliper guage is the way to measure.

They measure 4.18 to 4.2 with a digital calliper (depending on where on the shaft I put it). Must be a weird size.

Good idea on drilling/reaming smaller sizes - thanks.

Are there shaft adapters for DC motors usually used in toys so that I can use rods that are larger than motor shafts?

jeffmorris: Are there shaft adapters for DC motors usually used in toys so that I can use rods that are larger than motor shafts?

Whether you are looking for adaptors or couplers, when it comes to small sized parts in this area, you are likely to find that you will be spending a lot of money for one basic part. For instance, I just did some googling around for you for "miniature shaft couplers" and found more than a few suppliers, but all were either "call for a quote" (ie - meaning you can't afford what they want - or they want to sell you 1000 pieces), or for single units were around $25-35.00 USD.

A couple of things to look into would be shaft couplers for toys like Erector Set, Meccano, and VEX robotics - there is probably something in those you could use. You could also try to fabricate your own; you just need a small drill press, some thick-walled aluminium tubing, and a small tap/die set (plus small enough set screws). It isn't as hard as you think (but it does take patience and time).

You could also look and see what the R/C hobby world has to offer - plenty of parts and such there; maybe there are some shaft couplers or such you could use?

Another way you could adapt a motor shaft would be to take the motor shaft, measure it, and use a die to thread it; then take your larger shaft, drill it out, and take a tap to fit the threading you created on your shaft, then tap out the threads on the end of the larger shaft. Once you have that done, apply a bit of thread lock, and thread the motor shaft and the larger shaft together.