When using a router for applying profiles to the edges of a piece of stock, one thing that every woodworker must deal with is the potential for tear-out. Router tear-out can occur at nearly any point, but most often occurs on corners where the bit grabs end grain and splits it along the grain. Such tear-out will typically look like a chunk of wood torn out at the edge, an ugly problem to deal with.
Fortunately there are some steps that one can employ to help reduce such tear-out.
Use Sharp, Clean Bits:
Whenever using any woodworking cutting tool, having the cutting edges as sharp as possible is not only safer, but it produces better results. This is certainly the case when using router bits. Keeping the bits sharp and as free of pitch as possible will allow the bit to cut cleanly. If the bit is dull or laden with pitch, it will tend to grab and tear rather than making a precise cut.
Use Appropriate Bit Speeds:
When using a router, it's best to adjust the router bit speed appropriate to the size of the bit. The general rule of thumb is that the larger the diameter of the bit, the slower the speed that should be used. Adjusting the speed appropriately will keep the bit cutting cleanly and reduce heat build-up and burning.
Employ a Sacrificial Block:
As mentioned earlier, tear-out typically occurs on corners. One way to help reduce tear-out on corners is to position a piece of stock (the same thickness as the workpiece) at the end of the edge being routed. The bit will then keep cutting into this sacrificial block, not allowing the bit to grab the end grain. This method is most often employed when routing on a router table, but can be used when hand routing by clamping the sacrificial board in place next to the workpiece.
Route the End Grain First:
If your workpiece will require routing both along the end grain and with (parallel to) the grain, you'll see better results if you route the ends first. Because tear-out most commonly occurs on the ends, if you do have a bit of tear-out when cutting the ends, routing the sides (with the grain) afterwards will likely allow the cutting profile to cut the section that was torn out.