Minimizing Tearout

Each tooth on a saw blade slices through the wood with the action of a miniature chisel. The edges of the wood where the blade enters are usually smooth, because when the cut begins, the blade is like a chisel diving into the lumber. But the exit wound -- where the blade leaves the wood -- is often messy. That's because the wood fibers split away under the pressure of the advancing blade.

It's easy to understand the entry and exit sides of wood cut with a conventional handsaw because the blade cuts on the push stroke. The teeth enter the wood at the top and exit at the bottom.

But things get a bit confusing when the teeth spin around in the form of a circular saw blade. When mounted in a handheld circular saw, the blade enters the bottom of the wood and exits at the top. But when the blade is in a table saw, the teeth enter the top surface of the lumber. Thus your best board surface should be up when cutting at a table saw, the best surface down when cutting with a handheld circular saw.

When you need a clean edge on a piece of plywood, improve your odds by scoring the cut line with a sharp utility knife. The blade severs the face veneer that could chip. Crosscuts are more likely to produce chipping than rip cuts. The X mark on the board indicates the waste side of the cut.

Tape along a cut line will help prevent tearout. The upper surface of a jigsawn board is generally rougher than the bottom, but you can tape top and bottom if you want. If your saw has an adjustment for orbital action, turn it to minimum for smoothest results.

When you use the miter saw like a chop saw, the blade arcs downward and backward. This motion produces a smooth cut on the face and top edge of the stock. You can get tearout on the back surface and lower edge of the wood, but both areas are usually hidden when you install the molding.

With a push cut, the blade of the sliding miter saw enters the face of the board that's against the saw's platform. The fuzzy upper face of the board indicates that it is the exit surface. The upward spin also explains the blade's tendency to lift the stock.

Stack-cutting several flat boards at once keeps tearout to a minimum. The cut line has maximum support along its edges, so the only board with an exit surface on its face is at the bottom of the stack. Placing a sacrificial scrap board at the bottom of the stack ensures that all of the ones on top of it won't have an exit face.