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    How to Tame Tearout on the Miter Saw





    Wood is an amazing material, widely available in all sorts of colors, with beautiful grain patterns. It cuts easily with small machines and tools—products that are accessible to the home craftsman—and its strength-to-weight ratio rivals high-tech materials. But it is organic, and therefore comes with some strings attached.

    Tearout

    Support the wood fibers. The secret to taming tearout is to support the fibers with zero-clearance plates or sacrificial fences

    One is movement, and there is no stopping it. The other is tearout. A budding hobbyist soon encounters splintered edges and pockmarked surfaces, damage that grows more obvious when finish is applied. It happens with almost every tool in the shop. The good news is that it can be stopped, in most cases easily.

    Tearout: Caused by unsupported wood fibers
    Tearout happens when wood is cut and its plant fibers aren’t held firmly in place. There are two main types: One happens when wood is cut across its grain—this is what happens when using a miter saw. The other when the surface is planed.

    The problem with crosscutting is that it applies pressure across every fiber in a board. That’s fine through most of the cut, but near the bottom or back edge, the last few fibers have nothing behind them and would much rather splinter away than be sliced through. On most tools, there is nothing there to stop them.

    Manufacturers build those tools to make both square and angled cuts, so the opening in the table or fence needs to be extra large to allow the blade to be tilted. Carpenters don’t mind, because tearout doesn’t matter on framing, and they usually can hide the bottom side of a trim- or deck board. But furniture makers can’t always hide a splintered edge, and they quickly learn to close up that big gap with a “zero-clearance” plate or fence, usually just a piece of plywood tacked or clamped onto the tool. (See photo at top of page).

    For clean miter cuts, the best option is to add sacrificial fences. This L-shaped auxiliary table supports the bottom and rear of the stock when cutting small parts.

    Sacrificial fences

    Images: Steve Scott. Drawings: Bob La Point

    Excerpt from Christiana’s March/April 2010 (FWW #211) article “How woodworkers tame tearout”.
     


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