The jointer is one of those “heaven or headache” tools. When it’s working properly, it makes quick, sweet work of straightening and flattening boards. However, a poorly-tuned jointer can cause no end of frustration, yielding crooked edges, weirdly tapered pieces, and washboard surfaces.
Though a relatively simple tool, the jointer requires an exacting setup. Fortunately, it’s not that difficult to tweak the tool into proper working order. All you need is a good straightedge, a simple shop-made jig, a few common workshop tools, an automotive feeler gauge, and a bit of patience. The set-up sequence involves checking the tables for flatness and parallelism, correcting them if necessary, and then adjusting a set of sharp knives to the proper height. The entire procedure should only take an hour or so, paying big dividends in accuracy and time saved down the line.
Check the tables
Make sure your outfeed table is set to its proper height in relation to the cutter head and knives. As shown in the drawing on the facing page, it should be level with the knives when they are at the top dead center. Check this with a straight piece of wood (about 1/2× 11/4× 18). With the machine unplugged, rest the piece on the outfeed table with about 2 extending over the cutter head. Rock the cutter head while adjusting the outfeed table until a knife just barely grabs the piece. Lock the table.
Check each table for flatness as shown. Humps or dips can compromise operational accuracy. If a tune-up doesn’t correct problems, it may just be time to invest in a better machine.
Next, check to see if the tables are parallel, as shown. If the tables are out of parallel, you’ll need to adjust one of them, as discussed below. If they are parallel, skip to the next page, and focus on the knives.
The tables on most jointers ride on dovetail ways. A flat metal bar called a gib ride between the mating dovetails on one side of the machine. The gib and its adjusting screws remove the slop from between the table and the base while still allowing the table to move for adjustment.
It’s best to shim the outfeed table to correct non-parallelism, but if your jointer doesn’t allow that, shim the infeed table instead. Loosen the gib screws enough to allow a bit of table lift, and insert matched metal shims between the ways to elevate the appropriate end. (Aluminum shims cut from a soda can work fine.) If the table needs raising near the cutter head, insert the shims at the upper end of the ways. If the table sags at its outer end, place the shims at the lower end, as shown. When the tables are parallel, snug up the gib screws just enough to stabilize the table while still allowing it to move.
Feeling for flat. Check each table for flatness using a precision straightedge, gauging any gaps underneath using an automotive feeler gauge. You may be able to file or sand out a high spot, but it isn't much you can do for a dip.
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