43 - Build Your Own Dovetail Jig, страница 13

it's a tough, dense material. This makes UHMW plastic ideal for use as a runner in the miter slot of a table saw, see photo 'E.' UHMW plastic even comes in thin, self-adhesive strips that work great as a facing for an auxiliary fence, see photo 'F.'

stability. UHMW plastic is also very stable, and it won't absorb moisture. So once you cut the runner to fit the miter slot, it won't bind (or get sloppy) with changes in humidity.

availability. As with phenolic, you won't find UHMW at the local home center or hardware store. But it is available from the mail-order sources listed in the margin.

A UHMW is the choice for a stick surface. It's available from the following:

• Lee Valley 800-871-8158

• Rockier 800-279-4441

• Woodworker's Supply 800-645-9292

• UHMW

like to use a material called Ultra-High Molecular Weight (UHMW) plastic, see margin.

self-lubricating. The thing that makes UHMW plastic so slick is its self-lubricating property. Parts slide along like they're on ice. But UHMW plastic isn't as fragile as ice —

F. Fences. To make a workpiece slide easily along an auxiliary fence, add a strip of UHMW plastic.

For the parts on some projects, laminate and phenolic provide a nice, smooth surface for things to slide easily. But there are times when that's still not slick enough. So when I need an almost friction-free surface, I

E Runners. Jigs slide easily when they're guided by a runner made from a piece of UHMW plastic.

Acrylics & Polycarbonates

One final group of plastics that I use frequently is acrylics and polycarbonates, see margin.

clear. The main reason is they're clear (or lightly tinted). So it's easy to see exactly what's happening. I like to use them for safety guards, hairline indicators and router base plates, see photos below. Even though they look similar, there are a few key differences between the two plastics.

acrylic. Acrylic is clear, strong and quite rigid, so it's often

used as a substitute for glass. The only problem is it can shatter.

polycarbonate. So when I need something that's virtually unbreakable, I use polycarbonate. (It's even used in some safety glasses.) This makes polycarbonate best for a safety guard or cover where it might get hit by a chunk of wood or the edge of a blade or bit.

scratches. Regardless of which type you use, both acrylics and polycarbonates are similar in one way. They scratch easily. So after awhile, base plates and guards will be crisscrossed with fine scratch marks which makes

G. Guards. Because they don't shatter, polycarbonates work best for see-through guards.

H. Indicator. A hairline mark on a piece of acrylic makes it easy to precisely set a measurement.

them hard to see through.

availability. The nice thing-is acrylics and polycarbonates are fairly inexpensive. So you can make replacement parts whenever you need to.

You can usually find acrylics (like Plexiglas and Lucite) and polycarbonates (Lexan) at your local home center. But there are other sources.

For example, at a local company that manufactures plastics, I only paid seventy-five cents a pound for some scraps of clear plastic. For tinted versions, it's about twice as much.

I. Base Plate. An oversized piece of clear plastic makes it easy to see exactly where you're routing.

k Acrylic and polycarbonate plastics come in a wide variety of sizes and colors, making it a very versatile plastic for the shop.

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