What Is a Jamb Saw?

A jamb saw uses a round blade similar to a circular saw.

When installing flooring, one issue consistently comes up. The issue is what to do when you reach the bottom of a door jamb. There are several options. You can add trim to cover the inevitable gap that will exist between jamb and flooring. You can try to "cope" or cut the flooring to fit around the jamb, which can leave ragged edges. Or you can cut the jamb so that the flooring runs smoothly under with a tight joint. The best tool for the job is an undercut saw, commonly called a jamb saw.

Cutting the Jamb

Traditionally, the jamb and surrounding trim would be cut to set on top of the flooring. Today, retrofitting as a result of remodeling is a common practice. To cut the jamb to fit, many carpenters use a handsaw. The jamb is marked, using a piece of flooring as a template, and the jamb is cut on the mark to shorten it sufficiently to allow the flooring to slide beneath the edge of the cut jamb.

The Saw

The undercut saw is a close cousin to the common circular saw. It uses a similar motor and blade, with one exception. Instead of protruding from the belly of the saw, the blade of the undercut saw sticks out the front and is driven horizontally, to make cuts parallel with the floor. Jamb saws adjust in height and can be locked in place anywhere from less than ¼ of an inch to a little more than 2 inches above the floor to cut the jamb at the precise height needed.

The Blade

The standard size of the undercut saw blade is 6 1/2 inches in diameter. Construction is similar to a circular saw blade, with a row of teeth around the circumference of a round blade with a round spindle hole in the center for mounting. Blades can be purchased with tungsten steel, carbide and diamond tips. Specialty blades for concrete and masonry are also available. The blade is installed, similar to a circular saw, with a single arbor nut and washer from underneath the saw, using a standard wrench.

Adjusting the Saw

There are two adjustments on an undercut saw. The first governs how far the blade protrudes and controls the depth of your cut. This is typically set to just a little more than the thickness of the jamb or other trim being cut, to ensure a clean cut. The height of the blade from the floor is set using a scrap of flooring on top of any underlayment that will be used. Once the height adjustment has been released, typically with a screw-down toggle, the blade is raised or lowered to meet the top of the flooring.

Saw Operation

The cut is made with the saw firmly on the floor and the blade near the surface to be cut. Once the blade is up to speed the operator guides the saw forward to cut into and through the jamb. The cut is made from left to right to prevent splintering. Any remaining bits that the saw cannot reach can be cut with a hammer and chisel.

References

• Hardwood Installer: Jamb Saws