How to Set Up a Drill Press for Square Holes in Wood
What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
A drill press can cut a square hole in wood, but not with an ordinary twist bit. The usual setup uses a hollow mortising chisel around a square auger bit: the auger removes most of the waste, and the chisel pares the corners. A mortising attachment can turn a compatible drill press into a useful mortiser, though it takes careful setup and slower feeding than drilling round holes.
Before buying anything, check that the attachment fits your press. A mortising kit needs a suitable quill or chuck arrangement, enough clearance between the spindle and column, and enough quill travel for the chisel. It also needs a stable table and a way to hold the work securely. If your press cannot accept a compatible attachment or has too little clearance, a dedicated mortiser—or cutting the joint by hand—may be the better choice.
Contents
Choose the right setup
A bench mortiser is built for this job. A drill-press mortising attachment costs less and saves space, but it can be fiddly to align and may flex more under load. Hand-cutting is inexpensive and avoids buying a machine, though repeatable, narrow mortises take practice. For occasional furniture repairs or a few simple joints, the attachment is often adequate; for frequent production, the dedicated machine is easier to use consistently.
| Method | Best for | Main trade-off |
|---|---|---|
| Drill-press mortising attachment | Occasional mortises using a compatible press | Setup and alignment take time; press rigidity matters |
| Dedicated mortiser | Repeated joinery and longer work sessions | Higher cost and another machine to store |
| Chisel and mallet | A few holes, repairs, or shops without suitable machinery | Slower and more dependent on hand skill |
For an attachment, look for a complete drill-press mortising attachment kit with the correct mounting parts and hold-down. Check the manufacturer’s fit instructions against your drill press rather than assuming a universal fit. You will also need a sharp chisel-and-auger set sized for the mortise. A basic set can be sufficient for occasional softwood work; better-ground chisels are worth considering if the cheap ones arrive dull or need frequent sharpening.
Check fit and safety
Unplug the drill press before installing the attachment, changing bits, or adjusting the chisel. Follow the attachment maker’s instructions: mounting arrangements differ. Confirm the chisel is firmly held, the auger is centered inside it, and the chisel’s cutting edges face the correct direction. The auger should project slightly below the chisel point—commonly about 1/16 inch, though the kit instructions take priority. Too little projection can make the chisel rub and bind; too much can leave a ragged hole or overload the bit.
Rotate the spindle by hand through a full turn with the machine unplugged. Check that the auger clears the chisel on all sides and that nothing strikes the table, fence, or hold-down. Set the chisel’s distance from the work to suit the material: many setups leave roughly 1/16 to 1/8 inch between the chisel and wood, but verify the attachment’s instructions. This gap allows chips to escape. Too little clearance packs chips inside the chisel; too much can cause a torn, poorly defined cut.
Clamp the work to the table. A fence helps keep a long mortise straight, but it does not replace a clamp: the chisel can catch and spin the stock. Keep hands out of the cutting area, wear eye protection, and tie back loose clothing and hair. Do not wear gloves near rotating machinery.
Set speed and depth
Use the slowest practical speed recommended for the bit and press. Mortising creates more resistance than ordinary drilling. A 1/4-inch mortise often runs comfortably in the neighborhood of 1,000 to 1,500 RPM; larger chisels generally need slower speeds. These are starting points, not universal settings—follow the bit maker’s guidance and reduce speed if the press struggles, the cut burns, or chips stop clearing.
Set the depth stop before cutting. For a 1-inch-deep mortise, for example, limit the chisel to that depth rather than relying on feel. If the press has less than 1 inch of quill travel, plan on repositioning the work or adjusting the setup without losing alignment. Do not force the quill to reach a depth the machine cannot safely provide.
Cut the mortise
Mark the mortise clearly, then align the chisel point at one end. Make a short test cut in scrap of the same species and thickness. Check the corners, depth, and fit of the mating tenon before committing to the workpiece. A mortise that is too tight can split the board when assembled; one that is too loose weakens the joint.
Start at an end of the layout and work along its length in small, overlapping plunges. A spacing of about 1/8 inch is a practical starting point for a narrow mortise; leave less material between cuts in dense hardwood or with a small, less rigid press. Do not push the chisel straight through a long stretch of uncut wood. That forces the corners to shear too much material at once and can cause binding or a chipped edge. Withdraw the chisel often enough to clear chips, especially in deep cuts, and let the motor reach speed before feeding.
Feed steadily, not forcefully. If the handle takes much more pressure than it did on the test cut, stop and check for packed chips, a dull chisel, excessive speed, or too much auger projection. A squealing or burning cut is a warning, not a cue to lean harder. Unplug the press before clearing a jam. When the mortise is complete, inspect the bottom and walls; pare isolated high spots with a sharp chisel rather than forcing the attachment to correct a poor setup.
Common problems and fixes
Rounded or torn corners usually point to a dull chisel, misalignment, or aggressive spacing between plunges. A ragged bottom can result from chip packing or a blunt auger. If the work shifts, improve clamping before continuing; tightening the fence alone is not enough. Repeated slipping, excessive vibration, or a chisel that will not stay aligned suggests the press or attachment is not rigid enough for the job. In that case, stop and use a dedicated mortiser or hand tools rather than risking a broken bit or damaged work.
A well-set drill-press attachment can make clean square mortises without buying a separate machine, especially in softer woods and modest quantities. Its limits are rigidity, chip clearance, and setup time. Take a test cut, clamp the stock, and let the chisel do the work; those steps matter more than buying an elaborate kit for an occasional joint.
