Been there, done that. Still there, actually.
Firstly, I wouldn't spend money on a stepper motor to use for this, because the chances of it working out are fairly slim and then you've wasted the money unless you can send it back and pay the shipping all over again. I get the impression that you're in the UK and I don't know what things are called there. Here in the US we have "dumps" or "transfer stations" where people bring trash to get rid of it. Electronics are supposed to be in separate categories (to be recycled), but they often get mixed into the regular trash because sometimes electronics collections only happen at certain times of the year and sometimes it costs money to throw out electronics. Sometimes you can find things out on the street on certain days. My point is, I guess, that you're probably almost as likely to find a suitable stepping motor in the trash as you are by paying money for one. It just takes patience and being willing to be seen rummaging.
If you think the steppers in your printer might be useful you're one up on the rest of us. Assuming you want to use your printer as a printer, maybe try looking on eBay for one of the same model cheap. I've read good things about pulling steppers out of used inkjet printers and flatbed scanners, but I haven't seen either in the trash here since I read about it. I don't know about steppers in laser printers, but I've got a few here at work I'm probably going to have to toss soon, so I plan to look in them.
I've tried stepper (and/or servo) motors from big 5 1/4 inch full height hard drives and some looked promising, but only at high speeds. I've got some hydro potential and spinning one at 3000 RPM isn't out of the question if I use a small 2 inch rotor. I've got some that put out 3 volts RMS 3-phase, with a 3 amp short-circuit current. I'm fiddling with voltage triplers, but got stalled by starting a RACA for wind use.
I used to have a job where I used lathes and milling machines, but I left there 16 years ago. I still miss a machine shop, but I'm limiting myself to what I can do without.
A while ago I thought of a way to do motor conversions without being able to turn down rotors, and I've seen at least 1 mention of it being done by someone else. What you do is scrounge. You can't turn down a rotor, so you use bits from different motors (auto alternators also useful). Find one with a small rotor that will fit inside of another motor with enough room left for magnets around the outside. Take the bearing mountings from the rotor and rig them to fit on the other motor however you can, like by using pieces of flat steel stock to mount them on and mounting the pieces to the bigger motor. How much air gap you have between the rotor and stator matters, and you want to keep it to a minimum, so you might want to order magnets to fit the gap after you've got the other pieces. Remember to figure in the diagonal measurement of the magnets, or maybe better yet make some mockups from wood to make sure they'll fit before you order. You'll probably need to collect a few motors before this will work.
I decided to start from scratch. I was impressed by the simplicity of the single magnet design at http://www.fieldlines.com/story/2006/10/15/23529/947 but if you read carefully you'll notice that he's only getting 1.8 watts out of it after the tripler.
So I decided to try a RACA (Radial Air Core Alternator) for my first attempt. I'm using a piece of 2-inch square steel tubing for the rotor part, to put my magents on. I cut two pieces of 1/4 inch steel to fit inside the ends of this, with holes drilled and tapped in the ends of them for screws that come through the square tubing. I drilled 3/8 inch holes centered as well as I could in these end pieces for the shaft, then drilled and tapped set screw holes for screws to keep it from turning on the shaft. Like many beginners, I'm using a 20 inch fan blade for a prop, which fits on the 3/8 shaft. I found new ball bearings at http://www.sciplus.com/category.cfm?category=177 for $2.50 a pair, and bought a 7/8 inch hole saw to make bearing mounting holes. That's the fanciest tool I've got. My base and the end pieces where the bearings mount are made of 1 inch x 2 inch oak. To make a mounting for the coils I bought a coupling for 3 inch PVC drain pipe, because it was about the right diameter and plastic. I cut a couple of cradle pieces from spruce to mount on the base and fit the pipe coupling into. Now I've got the whole thing spinning inside the pipe coupling, magnets and all. I'm at the point where I'm winding test coils and seeing what I get out of them at different speeds. So far the results aren't all that encouraging, so I'm going to bigger magnets and smaller
wire for winding the coils so they don't take so much room. With a 150-turn coil I'm getting about 2 volts peak-to-peak on a scope, spinning by hand at around 500 RPM, with a nice sine wave finally after adjusting the shape of the coil. Outdoors on a windy day with the blade on it was hitting peaks of 1.5 volts RMS on a DMM. That's with 1 test coil, and I plan on using 12 total, 4 per phase. I'm going to try a 300 turn coil next, along with bigger magnets when I get some flat head screws that don't stick up in the way of mounting them. It's fun, but it takes a lot of patience doing almost everything by hand. I've got an electric drill and the hole saw, but other than that it's a hacksaw and files doing most of the work. I'm measuring as carefully as I can to keep things centered and so far the balance isn't too bad. Most of the steel came from the dump and I already had the wood. The first magnets I was using were from 5 1/4 hard drives, but now I'm fitting a set of 4 of the typical size used in axial flux gennys, 2 x 1 x 1/2 inch. I hope to put up pictures eventually, but this is a long way from finished.
I guess the main thing you should strive for is to keep the cost down, learn something, and have fun. With a windmill in the stepper motor class it would take years to pay for itself in the electricity you save. In my case I've got a piece of land where I don't have grid/mains power and I just want to charge batteries to run LEDs, at least for now.
Alan
