Popular Woodworking 2000-11 № 118, страница 4

Popular Woodworking 2000-11 № 118, страница 4

If you're an electrical engineer, you can stop reading this article right now. This story isn't for the gear heads — it's for the rest of you woodworkers who use power tools every day but are occasionally stupefied by amps, volts, watts and horsepower. I'll warn you, there's just the tiniest bit of math to learn here. But if you can multiply and divide two numbers, you will open up a whole new world of understanding when it comes to the subject of motors.

The first thing to understand is that there are two kinds of motors that power almost all of the machinery in a home workshop: induction motors and universal motors. Each type has its strengths and weaknesses. The reason that you need to know the difference between the two is that some tools (table saws, planers and jointers, for example) can be powered by either type of motor. So you need to educate yourself so you'll choose the right motor for the kind of work you do.

In general, induction motors power stationary machinery that must run for hours on end, such as big table saws, planers, band saws and jointers. Universal motors power mostly hand-held stuff: routers, jigsaws and sanders. However, this is changing. These days you'll find more and more universal motors in bench-top table saws, small jointers, spindle sanders and portable planers.

I like to think of the two motors as the tortoise and the hare. Induction motors are the tortoise of the pair. They're rugged, quiet, large, heavy, turn more slowly and can be stalled under heavy use. They are great for the long haul. Universal motors, on the other hand, have a shorter life span, they're smaller, they make more noise, they operate at very high speeds, they offer the most horsepower per pound of any alternating current motor, and they are very difficult to stall. Universal motors provide large amounts of power in quick bursts with constant torque and at variable speeds.

It might help to think about how you use tools with universal motors. If you've got a chop saw, you need a burst of power for three or four seconds to make your cut. You need torque and you need it fast. Same goes for biscuit joiners and routers. Unless you are running parts for 100 doors on your router table, chances are that these tools are on for five minutes and then off for a while. Now think about how you use a jointer or a planer with a hefty induction motor. You might have 100 board feet of lumber to surface. Each board might have to go through that machine five times. Your machine might be running for hours on end.

So each type of motor has a type of job that it's really good at. And it all has to do with the

what you must know about

Learn to shop smart

so you get the right motor for the way you work.

by Christopher Schwarz