Routers are versatile and necessary. However, they can be tricky. They are different from many other tools in that the bit spins into the cut horizontally (vs. vertically as with saw blades). This requires thinking about things a bit differently.
When the teeth of a saw blade grab the wood, they pull it down towards the tabletop (unless the wood goes in badly and the blade doesn’t catch it straight on. Then you have trouble, namely kickback).
When a piece of wood contacts a spinning bit, as in a router, the wood pushes toward you or pulls away from you. It is critical to know the difference.
If you approach the wood correctly, the spin of the bit will push the workpiece into the fence (if you are using a table), or it will push the bit into the work piece (if you are using a hand held machine). The cutter pulls itself into the wood by the force of its spin.
If you go in the wrong direction (called back climbing or climb cutting) the wood will pull away from you. If you try to take a large cut going in the wrong direction the board can launch across the room, or, if routing freehand the tool can decide to take a trip of it’s own across the board. Therefore, the trick is to rout in the right direction.
So how do you decide which way to go? Unfortunately, there is no one direction, since sometimes the workpiece is on a table, other times the router rides above the wood. It also makes a difference if you are cutting on the inside or outside a board.
The way to think about direction of cut is to visualize the bit spinning. If you look at the tool upside down (for example when it is installed in a table) the cutter spins counterclockwise. When the router is on top of the workpiece (as when following a template or routing around the edge of a frame) the cutter is spinning clockwise.
Find the leading edge of the bit and make sure it pushes the wood back towards you. For example, if you are trimming the inside edge of a frame with a handheld you want to move clockwise, the outside edge go counterclockwise.
This is the correct way to rout and it is the safest. Until you are comfortable with your own tool you should only cut in the correct direction.
Now, having said that, there are times when a climb cut is
appropriate. A climb cut is when you deliberately rout in the wrong direction.
Some cuts produce considerable chip out on the back edge (especially in end grain). One solution is to place a sacrificial board behind your piece. This board will then take the tear-out instead of your workpiece.
However, you can also take a light climb cut. This scores the fibers and any tear-out will be back from the edge of the final cut. Then go back and finish the cut in the correct direction. This will get rid of any tear-out from the previous pass and leave a neater final cut.
Regardless of how or what you are routing, it is important not to take too big a pass. Trying to take off too much material in one pass can cause chip out or burn marks on your work piece. It is also possible to pull the bit out of the collet. Then you end up taking off even more wood and the bit comes further out. Not pretty.
So, the final word is to pay attention to your router. If you hear the motor straining, or if the cut feels choppy, back off and make your cut in several passes. Your work and your router will thank you.