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You can make a custom baseplate that'll accommodate standard template guide bushings. To bore the rabbeted bit opening, use two Forstner bits.

To ensure that the opening is concentric to the bit axis, mount the blank on the router and use a V-groove bit to just mark the center of the opening. Remove the baseplate from the router. On the drill press, first bore through the plate at the centerpoint with a '/«-inch drill bit. Switch to a IMvinch Forstner bit, and with an in-and-out action, drill the counterborc. The bit's center spur should locate the hole using the '/fe-inch center hole. Be sure you don't bore all the way through the plate, but do bore deep enough that the bushing's flange will be flush with or below the surface. Complete the hole with a l'/V-inch Forstner bit. Again, to bore the hole, feed the bit hard for a second, then back it completely out of the work. Feed again briefly, then back out. Repeat this in-and-out action until the bit completely penetrates the plastic.

bits and even Forstner bits work just fine. Drill the hole with an in-and-out action, so things have a chance to keep cool—cool enough, anyway, to prevent the plastic from melting. A standard countersink similarly works just fine for countersinking mounting holes.

Be particularly careful when drilling large holes, since this operation can create enough heat to soften the plastic and make it stick to the bit. If possible, use a good sharp hole saw at slow speed to cut the center hole in you r c us torn bases. Or try drilling a small hole, then enlarging it with a router and bit. If you have a template with the proper-sized hole—the factory baseplate, for example—attach it to your plastic with double-sided carpet tape. Drill a starter hole, then use your router with a flush-trimming bit or a pattern bit to enlarge the hole. Either bit's bearing rides the template, while its cutting edge makes the cut.

Bending Acrylics

The acrylics—and thermoplastics in general—have the useful property of becoming pliable when heated. This means you can easily bend them into new shapes. The working temperatures range from 250° to 300° F. which is within the realm of your kitchen's range and your shop's heat gun. (While this bit of know-how may not be useful in making baseplates, it may be handy in making router-table accessories and other jigs and fixtures.)

The general procedure is to heat the plastic, then form it quickly, before it cools. Because it has "memory." the acrylic has to be bent a little beyond any angle you want—say, 5

degrees beyond it—and allowed to come back to the finished angle. There you hold or clamp it for a few minutes until the plastic has cooled and recaptured its rigidity. Make a mold for the plastic, by all means, even if it is merely a wood block over which you bend and clamp the warm and pliant plastic.

Bear in mind that your acrylic will have rounded edges where you bend it. Thus, if you do use a wood block as a form, bevel its edges to accommodate this characteristic of the plastic. If a sharp interior corner is essential, you can achieve it by routing a V-groove along the axis of the bend before the acrylic is heated; the groove's depth should be half the thickness of the plastic. When bent, the groove will form a sharp inside corner.

The procedure isn't totally trouble-free, of course. Both under-heating and overheating cause problems. If the plastic is bent before reaching the proper temperature, small cracks, called crazing, may

Here's how we bent one of our acrylic bit guards. The acrylic is clamped between two wood blocks and heated with a heat gun. Play the blast of hot air back and forth along the area you will bend; in this case, you need two bends, which are close enough together that you can do both at once. .4s the plastic becomes flexible, use a third wood block—don't burn your hands on the plastic—to bend the plastic down and into. Clamp the block until ¡the plastic cools.

Here's how we bent one of our acrylic bit guards. The acrylic is clamped between two wood blocks and heated with a heat gun. Play the blast of hot air back and forth along the area you will bend; in this case, you need two bends, which are close enough together that you can do both at once. .4s the plastic becomes flexible, use a third wood block—don't burn your hands on the plastic—to bend the plastic down and into. Clamp the block until ¡the plastic cools.

appear. On the other hand, if the plastic is left too long in the heat, it will bubble and scorch, yielding an uneven, rippled shape. In either case, the bends will be weakened.

To make a single bend, you can probably heat the plastic satisfactorily with a heat gun. Otherwise, heat it in an oven preheated to 300° F. Lay the plastic—with the masking paper removed, of coursc—on a clean, flat cookie sheet and put it in the oven, leaving the door slightly ajar. A '/-»-inch-thick piece of acrylic should "bake" about 10 minutes.

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Wood Working for Amateur Craftsman

Wood Working for Amateur Craftsman

THIS book is one of the series of Handbooks on industrial subjects being published by the Popular Mechanics Company. Like Popular Mechanics Magazine, and like the other books in this series, it is written so you can understand it. The purpose of Popular Mechanics Handbooks is to supply a growing demand for high-class, up-to-date and accurate text-books, suitable for home study as well as for class use, on all mechanical subjects. The textand illustrations, in each instance, have been prepared expressly for this series by well known experts, and revised by the editor of Popular Mechanics.

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