Synopsis: A clamp won’t solve problems of bad geometry, but if the math adds up, a good clamp should accurately position stock and firmly close the joint, writes Anatole Burkin of Fine Woodworking. Nothing is more maddening than trying to get by with a clamp that won’t bring a joint home or won’t hold it securely while the glue sets. Here, he analyzes 20 miter-clamping devices and describes 16 of the winners and why they succeed. He assesses ease and precision of alignment, ergonomics, and pressure exerted (measured by using a feeler gauge in a joint and tightening the clamp). He rates the clamps as light, medium, or heavy duty, depending on their grip strength, and he gauges their overall performance.

A good miter joint begins with an accurate cut and ends with a precision clamp. Errors made along the way—a cut that’s off a degree or a clamp that won’t pull the joint tight—can get compounded. It’s like using a checkbook: mess up one entry and the entire running balance turns to slop.

A clamp won’t solve problems of bad geometry, but if the math adds up, a good clamp should accurately position stock and firmly close the joint. Nothing is more maddening than trying to get by with a clamp that won’t bring a joint home or won’t hold it securely while the glue sets.

There are a lot of ways to clamp miters, and readers of Fine Woodworking have come up with many ingenious solutions. Manufacturers have been prolific, too. I looked at more than 20 clamping devices currently on the market and included the best 16 in this survey. I evaluated the clamps on several criteria: ease and precision of alignment, ergonomics and pressure exerted on a joint. To measure the amount of pressure a clamp exerted, I slipped a 0.0015-in. feeler gauge into a joint and tightened the clamp.

If the feeler gauge slipped out with a gentle tug, I labeled the clamp light-duty. If a tight grip was required to remove the feeler gauge, I labeled the clamp moderate-duty. If I had trouble pulling out the gauge—or in some cases couldn’t pull out the gauge without mangling it—I described the clamp as heavy-duty. Overall performance ratings are as follows: adequate, good and excellent. I didn’t include any of our 20 test clamps whose performance was poor.

Miter clamps come in many varieties. Some wrap around the entire workpiece. Others grip one corner at a time. There are clamps more suited for trim carpentry or paint-grade work because they leave small teeth marks, which can be filled. Other clamps are geared for large jobs, and won’t perform well on small projects.

From Fine Woodworking #130

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