A discarded oven can still serve for projects other than welders or Jacobs ladders, in fact we will not be using the power transformer at all for this Instructable. The type of unit to look for is the over range style that has a built in squirrel cage exhaust fan. We'll harvest that and some other parts to make ourselves a versatile high volume "shop" fan, suitable for fume exhaustion as well as keeping things cool. It will be selectable in speed thanks to internal winding taps, be thermally protected, and very portable, so lets go!
Step 1: Hazardous Material Warning
Microwave ovens can harbor a lethal electrical charge in the capacitor, and may have other health issues as well. Before you begin it is strongly encouraged you do a search engine protocol for safety tips when dismantling this type of appliance. Much has been published both textually and visually- such as YouTube videos- so take your time and make sure you understand the risks as well as the protection procedures.
Step 2: Gather Components
Having employed all safety procedures, carefully dismount the motor, along with it's small 10 mfd. capacitor, snap switches, and wiring harness including the line cord if still attached. As the build progresses, you may substitute material you have on hand for what is presented, and that's o.k., nothing else is vital for the project. You may find the fan and parts greasy; simply wipe everything with a cleaner to restore them and make sure the blades are dirt free for smooth operation. The motors I've gathered in the past have all been thermally protected, and since that is a very desirable thing, make sure the declaration is present. I'm not an expert on this aspect, but I think it has to be so built in order to pass Underwriters Labs or C.S.A. approval, other countries may have different requirements though. This particular fan model is a continuous duty type which utilizes a run capacitor making it very efficient, and therefore perfect for this project
Step 3: Build a Control Switch
I wanted a center- off single pole double throw action. Of course such a switch is readily available from suppliers, but that is not the point of this Instructable, here it is learn by doing and also embraced is a waste not- want not attitude, thus the carcass will provide for most of the project needs. Study the images and take note that the actuator arm has an end notch that serves two purposes: it easily depresses the snap switches when rotated over the button, and it allows clearance for a center off function. Filing a slight bevel on each side of the notch eases the action without jamming. The button's return force is sufficient to maintain arm position during operation. For the base of the switch assembly I used a piece of old polyethylene cutting board, but any thick plastic or wood will serve as well. I used the contacts labeled N.O. (normally open) and C (the common), as I only want conduction when the button is depressed.
Step 4: Fabricate a Trim Shroud
I have a supply of ABS plastic on hand that I harvest from old C.R.T. television carcasses, sawing out the flats and shapes that I think may have some future use. It is easily machined and worked with ordinary tools and of course, free. I simply determined the desired width, and cut my workpiece long enough to take a 90 degree bend and cover two adjacent openings. A simple setup in the vise, a heat gun, and a wood block for pressing the work flat resulted in a decent looking trim piece, awaiting the drilling of mounting holes
Step 5: Make Ready for Wiring
A piece of scrap plywood holds the electrical system's components securely, with ample room for interconnections. This chassis will also provide a means for applying a protective trim cap.
Step 6: Fabricate a Trim Cap
This will protect the electrical system as well as provide operator safety. I simply cut a scrap wood form and again used the heat gun to soften the ABS and wrap it around the form for a 3 sided enclosure. It will be screwed to the chassis edges during final assembly
Step 7: Assembly Tips
This fan model has molded fastening points called "screw bosses", which are material buildups that are cored for threaded fasteners, I used them all for the build as they were conveniently located for my purposes. I wanted to be able to tilt the fan outlet from horizontal to vertical, a pair of salvage angle brackets made a gimbal mount for just such a need.
Step 8: Suggested Uses
It will excel at fume removal, since that was the original design use, so it's a very good soldering station companion. It also wall hangs quite nicely thanks to the gimbal base and carrying hole of the handle, needing nothing more than a nail or screw for support. Placed on a cement garage floor, it will direct upward the cooler air that inhabits that region, giving a refreshing breeze during hot weather.
Step 9: Parting Thoughts
Microwave ovens can of course provide a bonanza of parts, like the previously mentioned transformer and the useful timer board. The steel case can be recycled and the magnets around the tube are very powerful, even the perforated shield screen inside the door makes a serviceable sifter for sand and other particulates and also found useful are thermal protectors located in several critical areas. All in all this is a fun and practical old school build that is micro controller free, easy to do, and serves a very useful purpose in the home or shop. Do be advised that if used in the presence of small children, guards installed over the openings would be required; typical hardware cloth would do nicely for that.