9 Tips for Beating Router Tear-Out
Stop router disasters before they start.
by Eric Smith
Snap, crackle, crunch!
No, it’s not your breakfast cereal. That’s the sound of router tear-out.
Aaargh!
And that’s the sound of a woodworker facing a do-over or repair.
Tear-out can happen cutting across or against the grain, cutting too deeply, using a dull bit or just running into a hidden flaw. One thing’s for sure: It’ll always happen at the worst possible time. Although it can’t completely be avoided, you can definitely minimize the chances of tear-out by following some simple techniques and precautions—without adding a lot of time or expense to your projects.
Pay Attention to Grain Direction
Visualize a feather cut by a router. It would be a mess, of course, but the point is that when you rout against the grain (see photo, left), the wood reacts just like a feather. The grain is running right into the bit rotation. The wood’s fibers are likely to catch and break apart ahead of the cut, producing tear-out. But when you run the router with the grain (see photo, right), you get a smooth cut.
Feeding your stock so the grain direction crashes head on into the bit rotation is like running your finger the wrong way on a feather. Nasty tear-out is almost a sure thing.
Flip a board end for end to change the direction from which the grain meets the cutter. Now the grain flows in the same direction as the bit rotation. The result will be a smooth cut with little or no tear-out worries.
Make a Very Light Final Pass
Trying to hog out a clean edge in one pass is asking for tear-out trouble. Instead of gambling with an expensive piece of wood, take the time to make at least two passes: one heavy pass and a very light final pass.
Because the final pass is just a shaving cut, the bit is a lot less likely to catch and tear the wood fibers. You’ll get a smooth surface, even if the grain is going the wrong way.
Use a Down-Cutting Spiral Bit for Flush Trimming
Down-cutting spiral bits push down on the wood’s surface. The result is a clean, tear-out-free shearing cut. Down-cutting spiral bits work especially well for trimming or cutting through delicate veneers, melamine, laminates and highly figured woods.
Use a Zero-Clearance Fence
A zero-clearance fence backs up the wood as it’s fed into the router bit, making it difficult for the wood to chip.
To make a zero-clearance fence, set the router bit at the height and depth you want. If you have removable subfences, turn the router on and slowly slide the infeed side of the fence into the bit. If your fence has a fixed face, clamp temporary subfences on both sides. With the router running, loosen the clamps on the infeed fence enough to slowly slide the subfences into the spinning bit.
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