No matter how precisely you cut table legs to length, nor how carefully you glue up the legs, aprons, and top, your four-legged table may still rock or wobble a bit.
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No matter how precisely you cut table legs to length, nor how carefully you glue up the legs, aprons, and top, your four-legged table may still rock or wobble a bit. Just the act of attaching the top can pull one or more of the legs out of alignment. If it happens to your table, don't panic: Here's a simple way to wipe out wobble the first time.

The trick in solving this rocky problem: Remember that three points describe a plane. That's why a three-legged stool or tripod won't rock, but a four-legged table might. To determine whether your table will rock, first stand it on a dead-flat surface, such as your tablesaw top. If it wobbles, look for the two long legs that are diagonally opposite from each other. To remove the wobble, you need to trim the longer of these two legs. Position the table on the saw and then score lines on the "long" leg, as shown [Photos below].

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After determining which are the long legs, hang one over the edge of a reliably flat surface. (In most shops, a cast-iron tablesaw top or large shaper table fills the bill better than a wooden benchtop.)
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With the other three legs down tight against the top of the tablesaw, set a straightedge on top of the saw. Then score a line on the leg along the bottom of the straightedge. Repeat on the opposite face.

If the score lines are less than about 116 " from the bottom end of the leg, it may be easiest to just sand off the excess, as shown in the opening photo. Stick a piece of 80-grit adhesive-backed sandpaper to the top of your tablesaw, then work the long leg back and forth on the sandpaper to remove the excess.

If you have to remove more than 116 ", make a leg-trimming jig, shown below, that clamps onto the leg right at the score lines. We made this one from scraps of melamine because it has a smooth, slick surface, but you could use any hardwood.

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With the cutting guide in place, use a sharp, low-angle block plane or a flush-cut saw [Photo below] to trim the leg on the score lines. (Note: If you're using a block plane on a thin leg, clamp the leg securely in a vise or get a third hand for added support.)

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For removing 1⁄16" or more, clamp the cutting guide around the leg so its top aligns with the score lines on the leg. Hold a flush-cut saw flat against the top of the cutting guide and trim the leg along the score lines.

Finally, check the table once again on the top of your saw for wobble. If it's close, finish it off using the sandpaper method described previously.