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How to Tame Router Table Tearout
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.
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 and that’s where you get tearout on the router. The other when the surface is planed.
Crosscutting wood 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.
The trick to avoid tearout is to support the wood fibers with sacrificial pieces of wood or zero-clearance plates.
Although routers don’t exactly crosscut wood, they cut across the fibers in a similar way.
On router tables, the force of the spinning bit is horizontal, so you will sometimes need a zero-clearance plate on the fence, but almost never in the table. There are a number of ways to do it: Make the whole fence sacrificial and replaceable, attach a thin blank plate to the fence, or design a fence with replaceable inserts.
|Bury the bit in a sacrificial fence. A clean cut is crucial for delicate joinery like these sliding dovetails. Attach an extra board to the fence, then pivot the assembly into the spinning bit.|
For routing end grain handheld, you can also avoid tearout by attaching a sacrificial piece of wood to the end of the cut—you can just nail it in place with a pin nail, making sure that the nail doesn’t come in contact with the spinning bit.
Or, if you’re routing 360 degrees around a board, rout the end grain sides first, then rout long grain edges. This long grain cut should clear up any tearout from routing the end grain.
Photos: Steve Scott
Excerpt from Christiana’s March/April 2010 (FWW #211) article “How woodworkers tame tearout”.