Jim Chestnut's Clam Clamps

If you're a trim carpenter these might be just what you never knew you were always looking for. No really, if you've ever had your miters on your trim open with seasonal wood movement Jim's Clam Clamps can help. There's no getting around it, miters move during the seasonal changes in humidity. Your interior and exterior miters need to be reinforced or glued and clamped with pressure, ideally both, to prevent or greatly reduce movement. Biscuited, splined, Dominoed or just plain mitered joints need pressure for the glue to reach its full strength. Most common practices to put pressure on mitered joints are inadequate. You know, the old cross nailing through the edge of the joint, even spring clamps don't apply enough pressure. Check out Gary Katz's article on Miter Joint Movement.

Jim Chestnut makes these clamps for clamping mitered trim joints (like door and window trim). Their cam action applies a great deal of pressure to the joint allowing the glue to reach its full strength. The clamp has two brass jaws, when you turn the lever (half turn in either direction) a cam action moves one of the jaws in towards the point of the miter making a perfect joint. The points on the jaws bite into the trim hold tight.

You can see the jaw extended in the clamped position in the photo above.

There are four pins in each jaw, they're removable and there are tapped holes in the body of the clamp to store unused pins.

Here's a shot of the Clam Clamps on mitered scraps. The joint is perfect. The clamps can be used to preassemble trim or used in place on the wall. They've got adequate clamping for almost any size trim. Made from stainless steel and brass so they aren't going to rust (and get rust on your trim) when you get water on them from wiping your glue joints.

The clamps do leave holes in the trim from the pins. Like I said the pins can be removed so you could remove the middle two from each jaw for stain grade work.

The clamps can be removed when the glue sets, usually in about 20-30 minutes with PVA wood glue (yellow glue). In the picture above I'm able to put a lot pressure on this joint with 20 minutes of clamping time. The glue won't fully cure until 24 hours or so but the joint is plenty strong enough to move and install preassembled trim. I remember reading someone's advice from the JLC forum when installing preassembled trim on walls that are badly out from the jambs it's better to nail into the jambs only, wait 24 hours them nail into the wall. This is so you don't put too much torque on uncured glue joints. I don't often get into production trim work so I can get by with two sets of the clamps (four clamps), you'd want 3-4 sets for production work. These things aren't inexpensive, at the time of this writing the Clam Clamps are $75 (USD) for each individual clamp. But considering that they speed up your work, improve the joints and help your work withstand seasonal wood movement they are a good investment. Discounts are available when you purchase them in sets, the more you buy the cheaper they get. These clamps are built well enough to last more than a lifetime and are made completely in the USA. You can get more info on Jim's site, Miterclamp.com