A frame clamp is a device that is used to hold a picture frame or similar item square while gluing. The frame clamp has adjustments on all four sides that are used to create a clamping force for any size project. By clamping a frame in an adjustable frame clamp, perfectly square corners can be achieved while ensuring the frame remains flat and true.
There are many styles of frame clamps and all have distinct advantages. Metal or aluminum type clamps are typically less prone to glue sticking to them as the frame dries. The frame clamp can be made strong yet remain light-weight. The adjustable frames are also less vulnerable to stripping due to the steel threaded components and they can be adjusted to clamp differing angles on each of the frame corners.
Wooden frame clamps can be made very sturdy by using heavy hardwood as the clamp material. The wood gives the feel of old-world craftsmanship and can be made non-stick by the application of wax or by placing waxed paper between the frame and the clamp. The wooden frame clamp is best suited for frames utilizing 90-degree corners on all four sides.
For frames using compound angles in construction, a strap type of frame clamp is best suited. This type of clamp uses a leather or nylon strap to encompass the frame and is tightened to achieve a joint at each corner. The disadvantage of the strap frame clamp is its tendency to flex while the frame is drying. As the glue dries, the frame tends to twist in the strap resulting in a warped frame.
Some of the high-end metal frame clamps use a locking device on both the inside as well as the outside of each corner. By placing clamping surfaces on both sides of the frame, the frame is kept true and square as the glue dries. This is especially helpful when working with fragile frames. This type of frame is easily crushed and broken by clamping pressures that are too high. For odd shaped and even round frames, a steel banded clamp with plastic or aluminum holding jaws may be the clamp of choice.
While some low-end clamps are essentially nothing more than threaded rod with corner clamps connected to each other, they do an adequate job when dealing with the basic frame. Most professional framers will use a variety of frame clamp types, choosing each one based on its unique ability for a particular frame application.