While the table saw and surface planer are the tools of choice when a piece of stock needs to be cut to a certain thickness, neither of these tools can properly do its job until one edge or face of the stock is flat. The best power tool for that job is the jointer. A jointer quickly smooths and flattens the edge of a board while cutting it square to an adjacent edge. Once this is done, the board is ready to lie flat against a table saw fence or table for a straight cut.
How a Jointer Works
A jointer is little more than a rotating cutter head with two or three finely tuned blades in between two small, flat tables. The stock is pushed across the first table, called an infeed, past the cutting head and onto the second table, the outfeed. The outfeed table is the same height as the top of the cutting head, whereas the infeed table's height is adjusted to determine the amount of material to be shaved off from the cutter.
The jointer is also equipped with a fence that allows you to square up or bevel the edge of a board. When the fence is set perpendicular to the tables and cutter, running the stock against the fence while making successive cuts eventually squares up the two adjacent planes of the board. The fence can also be tilted to cut a bevel on one edge of a board.
Using a Jointer Safely
Although all jointers should have a spring-loaded blade guard that covers the exposed cutting head, you must take care to keep your hands and clothing away from the blades. This is especially true when jointing thin pieces of stock. Using a push stick or wood paddles will help keep your hands clear of the cutter. When appropriate, using a featherboard to hold the stock firmly against the fence or the table is a good idea.
It is safer to make multiple shallow passes on the jointer, removing a very small amount of material each time, than to take a larger bite in one pass. This approach also causes less stress on the motor and cutting head and produces a smoother, more predictable edge.
As always, read and follow all of the safety rules in the instruction manual that come with the jointer. And be sure to wear hearing protection and safety glasses when operating the tool.
Operating a Jointer
Stand on the side of the jointer opposite the fence and place the edge of the board to be jointed facedown on the infeed table and up against the fence. Start up the jointer and wait for the motor to come to full speed. Never attempt to begin cutting when the cutting head is at less than full speed.
Apply light downward pressure onto the stock as you begin to feed the board over the cutting head, using enough pressure to comfortably control the stock. Once the front of the piece has safely passed the cutting head, shift your weight forward and place your left hand onto the stock near the leading end as you continue moving the board ahead. As the rear of the stock approaches the cutting head, remove your right hand and move it onto the stock over the outfeed table, safely away from the cutting head. Keep moving the board until it clears the cutter.
Safely lift the stock and return to the starting position for another pass. The jointer will remove the same amount of material with each pass.
Straightening a Bowed Board
Straightening a severely bowed piece of stock requires a slight adjustment in technique. First of all, it is much easier to joint an edge where the bow is facing upward in the center of the board. Attempting to joint a piece of stock when it is rocking on the table is extremely difficult.
If you're forced to try to joint the edge with the bow in the center facing downward, you'll want to focus your pressure on the infeed table for as long as possible. This will keep you from simply repeating the rocking action as the stock passes the cutter. After a few passes, the board should begin to straighten out.
Squaring up a Second Edge
If the finished piece of stock needs four square edges, the next step after jointing one edge is to square up a second edge perpendicular to the first. Verify that the fence is square to the infeed and outfeed tables. Since the fence on most jointers can be beveled, it is a good idea to verify that the fence is at 90-degrees with a layout square.
Once the fence is 90 degrees to the table, squaring an edge is very similar to the basic jointing procedure, but in this case, apply consistent pressure primarily to the fence. Place the previously jointed edge against the fence and move the stock over the cutter, keeping your hands safely away from the blades. Make multiple passes until the edge against the tables is perfectly flat and square to the edge against the fence.
Once you have two perpendicular flat edges, a table saw, or surface planer can trim the stock to the final dimensions.
Additional Jointer Functions
Once you have a handle on the basics of using a jointer, there are some other useful functions you can experiment with. The fence on most jointers can be beveled up to 45 degrees. This allows you to joint mitered butt joints along the length of a board. You can also mark the start and stop points on the angled fence and create stopped chamfers on an edge by easing the stock down onto the blades, cutting between the marks and then raising the stock away from the cutter.