What is an Undercut Saw?

An undercut saw is a specialized tool designed to trim the bottom of door jambs and other obstacles, allowing flooring to slide underneath for a seamless fit. Its precise, flush-cutting blade ensures a clean, professional finish. Intrigued by how an undercut saw can elevate your DIY flooring project? Discover its uses and benefits in our comprehensive guide.
Alexis W.
Alexis W.

An undercut saw is a tool used in woodworking and construction. An undercut saw is very similar to a standard circular saw. In fact, it essentially is an upside down circular saw. Although it is used to cut materials, an undercut saw has a slightly different function and purpose than a standard circular saw.

When installing flooring materials such as wood in an existing home or building, it might be necessary to trim door jambs or trim so that the flooring will fit under the door. This is especially necessary when carpet is being replaced by a solid floor. When carpet is used, the jamb and trim is installed all the way down to the sub flooring, which creates problems when installing solid flooring. When a solid floor replaces carpet, it usually is necessary to cut the jamb and trim off just above the sub flooring. If this is not done, the result after butting the flooring up against the trim is an unattractive gap that extends down to the sub flooring.

Man with a drill
Man with a drill

The process of cutting the trim and jamb was done by hand before the invention of the undercut saw, since no tools existed that were able to cut parallel to the sub flooring and as close to the sub floor as was needed. The clearance between trim and floor typically is about 1.75 inches (about 4.45 cm), so the motors on common saws were too large to use in this space. The only options were to either cut them by hand or remove the trim and jambs and then cut them. Both options were time consuming and required a great deal of precision cutting.

Undercut saws consist of a rotary electric motor that drives a flat, circular saw blade in a horizontal fashion. The cutting assembly is guided by a base that provides not only a stable surface for cutting, but also a non-skid sliding action. The blade is attached to a flange that extends away from the plane, and this blade is then attached to a drive shaft and configured in a way that allows it to be used parallel to the floor.

The blade can be adjusted vertically, but the method of doing this has its shortcomings. It usually is a slow process, and the fasteners need manual adjustment. Because of the need for peripheral adjustments, it is often difficult to ensure that the blade remains level.

Undercut saws also typically provide a vacuum attachment for safety reasons. This attachment ensures that all cuttings are captured. Unfortunately, the peripheral height adjustments often interfere with the vacuum attachment, making the use of the undercut saw complex and difficult at times.

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      Man with a drill