Corner Miter Problems

[Greg Caputo]

Good Afternoon All:

I'm here today admitting a great deal of frustration, likely caused by operator error, getting my corner miters to line up correctly during glue-up. The piece I'm making requires edging on three sides. I've taken a great deal of care making the miters, lining them up, fitting them tightly, using biscuits to make sure the top of the edge lines up with the top of the case, and doing a dry clamp. So far, so good. But when the time comes to put the glue on, BANG....the miters don't line up. The corners either don't come together at all, or one piece slips past the other, or the glue sets too quickly to nudge the pieces into proper alignment.

I'm convinced this is something which I'm doing wrong or not doing at all. Any advice will be helpful.

Thanks to all.

Greg

[Chris Padilla]

Do you mark your biscuits and use the same ones you did from your dry run? In fact, do you mark EVERYTHING to make sure the dry run matches the glue run?

Assuming you answer "Yes" to the above questions, I would say that the biscuits fit too tightly in their dry state and when you glue them, they swell too much and cause you problems.

I love woodworking, making joints, dry fitting stuff together but hate, hate, hate glue up time!! I'm getting better at it but I'm always pouring sweat (nerves) while doing a complicated glue up no matter how many times I practice and think I'm prepared.

[Lee Schierer]

A trick for lining up mitered corners is to lay a piece of wide masking tape sticky side up on the table. Place one end of the mitered piece on the tape so half the tape is still showing. Then carefully place the mating piece so the sharp edge touches the sharp edge on the first piece and it is aligned top and bottom. Press the second piece down onto the tape keeping it aligned as you do it. Now you can pick up both piecs and fold them together using the tape as a hinge. The tape can be left in place for gluing.

Miter corners have considerable end grain and will soak up glue pretty fast. Either apply lots of glue so the joint isn't starved or "size the joint" with a diluted glue water mixture before final glue up.

[john bateman]

If your 3 sides are say, 2 short pieces with a long one running between them, as on a 12" x 36" shelf, you can try this:

Tape the 2 short pieces in place. Trim the long one to fit perfectly, then glue it to the shelf only...not to the other two pieces. Once the long piece has dried in place, you can glue the two short ones to it, without having it slide around.

[David DeCristoforo]

Assuming that all of the above suggestions have been tried and verified, I have found that the "best" way to glue up four sided mitered frames is to use four clamps. Lay two clamps on the bench and place your roughly assembled frame on top of them so that the clamp jaws "split" the miters. Lay the other two across the top so that the jaws "split" the miters in the other direction. Now, you can push the corners around by tightening one clamp while at the same time loosening another. It's hard to describe but you will see how it works as soon as you start messing around with it.