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    Miter Joint Basics

    The miter joint, seen at the corners of a picture frame, is a beautiful way to join wood pieces. It can be used to join the corners of a flat frame or a deep box, but in many cases it needs some reinforcement if it is going to stand the test of time.

    The miter joint will hold up just fine on its own if there isn’t much stress on it, as is the case with a picture frame or small box, but it won’t stand up well in a door, for example, without biscuits or splines of some kind in the joints, or a plywood panel glued into the door to add strength (see Frame-and-Panel Basics).

    A great thing about miter joints is that when you cut a bead or other molding on the inside of the frame, the molding will meet perfectly at the corners for a very clean look. Miters seem simple but they are actually pretty tricky to cut perfectly, and any tiny inaccuracies will show up. Little gaps are probably okay for window trim, which only gets a passing glance, but mistakes stand out in furniture.

    To cut accurate miters, you’ll need a very accurate miter gauge or a miter sled on your tablesaw. You can also cut them pretty well on a miter saw (chop saw), especially a good one with a good blade.

    The simplest way to cut good miters is with an accurate miter gauge on the tablesaw. Woodworkers also build special tablesaw sleds for miters.

    Miters are also hard to glue and clamp. They love to slip and slide during the process. Probably the best way to clamp a mitered frame is with a band clamp, which pulls all four corners together at once. As for a mitered box, there is a really cool trick: You can lay the pieces flat, put masking tape over the joints, and then fold the whole thing into a box, putting more tape over the last open joint.

    Mitered Boxes are Super-Simple

    Mitered boxes are usually made on the tablesaw, by angling the blade. You can also cut these joints on a router table, using a 45-degree bit.
    Here’s a great trick for clamping mitered boxes. First, flip over the pieces, line them up end to end, and tape three of the joints.
    Then flip the whole thing over, put glue in all the joints, and just fold it into a box. Don’t forget to insert the bottom if the box has one. Then you just put tape across the fourth joint and let the whole thing dry. Perfect joints every time.



























    For Stronger Joints, Size the Miters

    Here’s a tip for gluing miters: The end-grain likes to drink up glue, so put on a layer, let it soak in and dry for about 5 minutes, and then reapply glue before clamping the joint.
    For mitered frames, use a band clamp to get even pressure on all four joints at one time.