Hollow Chisel Mortiser: Complete Buying and Usage Guide

A hollow chisel mortiser cuts square holes in wood. It’s a specialized machine that does one thing well: making mortises for mortise-and-tenon joinery.

How It Works

The machine combines two cutting actions. An auger bit spins inside a square, hollow chisel. The auger removes most of the waste while the chisel squares up the corners. Push the workpiece against the fence, pull the handle, and you get a clean, square mortise.

Setup matters more than the machine itself. The auger needs to extend past the chisel by about 1/16 inch. Too little extension and the chisel clogs with chips. Too much and the auger breaks. Getting this right takes some trial cuts in scrap.

Who Needs One

If you make chairs, tables, or doors, a mortiser earns its keep quickly. Cutting mortises by hand takes practice and time. A drill press with a chisel attachment works but tends to chatter. A dedicated mortiser handles the job faster and cleaner.

For occasional joinery, hand tools or a router with a jig might make more sense. Mortisers take up shop space and represent a single-purpose investment.

Benchtop vs Floor Models

Benchtop mortisers cost less and store easier. They handle most furniture-scale work adequately. The Delta and Jet benchtop models have been around for years with decent reputations.

Floor models offer more power and rigidity. They handle larger stock and deeper mortises without bogging down. Powermatic makes well-regarded floor mortisers, though they cost significantly more.

Chisel Sizes

Common chisel sizes run from 1/4 inch to 3/4 inch. Most furniture work uses 3/8 inch or 1/2 inch chisels. Smaller chisels heat up faster and need more frequent clearing. Larger chisels require more motor power.

Quality chisels matter. The cheap chisels that come with benchtop machines often disappoint. Replacement chisels from reputable brands cut cleaner and last longer.

Tips for Better Mortises

Take shallow bites. Trying to hog out a full-depth mortise in one pass strains the machine and burns the wood. Multiple passes of 1/4 inch depth work better.

Clear chips frequently. Wood chips pack into the corners and cause the chisel to bind. Backing out periodically keeps things running smoothly.

Keep chisels sharp. A dull chisel tears rather than cuts, leaving rough mortise walls that weaken the joint.

The Bottom Line

A hollow chisel mortiser speeds up traditional joinery significantly. It’s not essential—people made furniture for centuries without them—but it removes a bottleneck from the workflow. If mortise-and-tenon joints appear regularly in your projects, the tool pays for itself in time saved.