Thanks for all the useful information from different perspectives. I'm
starting to assemble some ideas about the kind of machine I might build
and the parts I'll need.

I think I have a suitable motor which I picked up from a skip when a
laboratory was being cleared last autumn. It's a shaded pole induction
motor rated at 30 W and it's really nicely built (they don't make them
like this anymore). It took me a while to work out the motor speed as I
sold my tachometer when I needed some cash. So I put a sticky label on
the shaft and held a pencil against it so it made a clicking noise. Then
I recorded the sound on the computer and looked at the waveform, and it
turns out the motor runs at 1425 rpm. I took a picture of the motor and
put it online:

http://www.mythic-beasts.com/~cdt22/...pole_motor.jpg

The most important question is how big a barrel I can turn with this
motor? I found one page showing a Thumler tumbler which had a 22 watt
motor, but it didn't list the barrel capacity. I was thinking of two 1.5
lb plastic barrels, which are 11.5 cm diameter, but they're actually
pretty small. The rubber 2.25 kg barrels (17 cm diameter) look nice but
they're expensive. I also have a 50 W at 950 rpm shaded pole induction
motor. It suffered a bit when the shed roof leaked, but it could
probably be restored. The 30 W motor has the advantage of being totally
enclosed so that no gunge can get inside, whereas the 50 W motor is
open. What do people think about power requirements?

I've found a 2.5 mm pitch toothed belt and aluminium pulleys for about
£12, which will provide the right reduction, and I can buy 15 mm round
stainless bar to make the rollers (about £4 for each roller). But the
bearings seem to be a problem. I really wanted to use those nice
self-aligning ball races in cast iron pillow blocks (probably with a 10
mm bore), but they cost a fortune - about £20 each! I could perhaps
afford £20 for all four. Any ideas where I might find surplus bearings
in the UK? I want the quality of my machine to be decent but I can't
afford to spend £80 on bearings. What do people think?

Once again, thanks for all the ideas.

Best wishes,

Chris