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Home Improvement : Ordinary-Looking Sander Boasts Many Uses : Woodworking: Random orbit sanders have been used by auto body shops, operated on air pressure. Now a model is available that runs on electricity.

Over the years, a lot of friends have asked me what’s the most useful type of sander for do-it-yourself woodworking. And my answer has always been something of a hedge.

“Nothing can match the speed and power of a good belt sander,” I usually say. But then I’d turn around and warn that a belt sander can also work too fast, and in the hands of a rookie, it can create some pretty deep gouges and depressions in a matter of seconds.

So for all-around versatility and user-friendliness, I’d recommend a good orbital sander . . . specifically one of the smaller types called “palm sanders” made by Makita, Ryobi, Porter-Cable, Black & Decker and others. But then I’d have to point out that orbitals are painfully slow if you have a lot of heavy sanding to do.

And finally--because they are too difficult to control and because they create horrendous swirl marks--I would dismiss disk sanders as totally out of the question.

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Just recently however, a new sander made by Porter-Cable has appeared on the market, and it may be the most useful type available (shown in the sketch).

“But that looks like an ordinary disk sander!” you say. Well it may look like one, but it isn’t. It’s a new type called a random orbit sander. Actually, random orbit sanders aren’t new.

They’ve long been used in auto body shops and in factories. But they’ve always been pneumatically powered by air pressure, and that has kept them out of the home market.

That changed when Porter-Cable introduced an electric version a few months back. If my guess is right, other makers will probably follow suit. The random orbit design is just too good to ignore.

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How It Works. Conventional orbital sanders all work on the same principle. An eccentric drives the sanding pad in a circular orbit, much the same path your hand would take when wiping a window with a circular scrubbing motion. To reduce the likelihood that the sander will create visible circular scratch marks, these sanders keep the diameter of the orbit small, about one-thirty-second inch or so. Trouble is, the smaller the orbit, the slower the sanding.

The random orbit sander takes a different approach. Its eccentric drives the circular pad in a large orbit with a diameter of about half an inch. This increases sanding speed greatly.

Normally, an orbit this large would create visible swirl marks, but the sanding pad doesn’t just orbit. It’s mounted in a ball bearing so it’s free to spin on its axis, totally at random, which is exactly what it does once you press it to your work and the friction of sanding comes to bear. The combination of orbital and spinning action breaks up any swirl marks before they can form.

What does all this mean in practice? You can sand at close to belt sander speeds with coarse 8O-grit paper, then switch to 100 and then 150 grit paper to get a super-fine finish. And the sander doesn’t really care about grain direction.

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This makes it perfect for those tricky situations when you are sanding two pieces of wood joined at right angles as shown in the sketch. If you attacked this joint with a belt sander, you’d always be sanding one piece across the grain, creating unsightly cross-grain scratches in the process. With an orbital, grain direction is immaterial.

Porter-Cable’s random orbit sander takes self-adhesive 5-inch disks, a system I have grown to like. Disks press on and peel off in a second, and if you keep the sticky side free of dust, you can remount it several times. Swapping disks is so easy you don’t give it a second thought.

There are a few tricks to using this sander. First, you press its pad flat on your work, you don’t tip it slightly on edge as you would a disk sander.

Second, be sure the pad is down flat on your work surface before you turn on the sander. If you start it in the air and then lower it to your work, it will behave something like a disk sander until sanding friction sets the pad into random motion.

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Third (related to the second), don’t expect to feather your work by using the sander with a light touch. If you fail to keep downward pressure on the pad, it will break out of its random orbits and start acting like a disk sander.

Fourth, you’ll probably have to use both hands to keep this tool under control.

And fifth, be careful if you try to use the random orbit sander on moldings, sharp corners, edges and the like. It may sand faster than you expect.

This new sander lists for around $205, but I ‘ve seen it in catalogues for well under that. Trend-lines, (800) 343-3248, sells it for $140.

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