Mortising with a Drill Press: What to Measure Before You Buy

All Posts benchtop drill presses Noah Carter Last updated on February 11, 2026

You can cut a mortise with a drill press. Woodworkers have been doing it for over a century. The attachment that makes it work - a hollow mortising chisel with a drill bit running through its center - is still available, still inexpensive, and still functional when set up correctly.

What nobody tells beginners is that your drill press needs to meet a short list of conditions before an attachment is worth buying. Buy the kit for the wrong machine and you’ll spend the weekend fighting the tool instead of cutting wood. Here’s exactly what to check, which attachments are worth ordering, and which drill presses handle mortising best.

How Hollow Chisel Mortising Works

The mortising chisel is a four-sided hollow square steel tube, sharpened at the bottom edge. A drill bit runs inside it. When you plunge, the bit clears out the bulk of the material while the chisel’s four edges pare the walls square. Move the workpiece over by the chisel width and plunge again. Overlap the cuts slightly and you get a clean rectangular mortise.

The attachment - called a mortising attachment kit or mortising jig for drill press - clamps to the quill of your drill press and holds the chisel square to the work surface. The bit mounts in the chuck above it. A fence and hold-down assembly keep the workpiece indexed correctly.

It sounds simple because it is simple, when everything fits. When it doesn’t fit, you get a chisel that’s slightly off-square, vibration that snaps small chisels, or a column collar that won’t grip your quill diameter. This is why measuring first is not optional.

The Three Measurements That Determine Compatibility

1. Quill Collar Diameter

The mortising attachment slips over the quill housing - the cylindrical housing that the quill (and spindle) travels through. Every attachment ships with a set of adapter bushings that reduce the attachment collar down to fit different quill housings. The Grizzly H7789 and Shop Fox D4031, for example, both cover quill collar diameters of:

2.95” (75mm)
2.60” (66mm)
2.36” (60mm)
2.17” (55mm)
2.00” (50mm)
1.89” (48mm)
1.57” (40mm)

Measure the outer diameter of your quill housing with a caliper. Match it to the nearest ID bushing in the kit. If your machine is a Grizzly G0485, Shop Fox W1680, Shop Fox M1039, or any of the common Taiwanese-sourced 15-17” imports, you will almost certainly land within this range.

The kits explicitly note they are not intended for small or “baby” drill presses - typically anything with a 10” or smaller swing. The quill housing on those machines is too small for the standard bushing range and the motor is often too underpowered to drive the chisel cleanly.

2. Quill Travel (Spindle Travel)

Mortising chisels for a drill press typically need at least 3.5” of quill travel to cut a mortise of useful depth. Most 12-15” drill presses give you 3-3.5” of travel. Larger machines like the Grizzly G0485 (17” floor standing) give you more.

Standard furniture mortise depths run 1” to 1.5” for through-tenon joints and 1.25” to 2” for blind mortises. If your machine only gives you 2” of quill travel, you’re already limited on typical furniture work.

3. Table Rigidity and Motor Power

Hollow chisel mortising puts a different kind of stress on a drill press than drilling. The chisel resists rotation - you’re not spinning it, you’re pressing it straight down with the bit rotating inside it. This requires a machine that doesn’t flex at the table or the column under downward load.

The JET JDP-17M (17” floor-standing with mortising table) is explicitly spec’d for this. The Delta 11-990 mortising machine is a dedicated unit. For a benchtop press, you need a machine with at least a 1/2 HP induction motor (not universal motor) and a solid cast-iron table that doesn’t rock when you lean on it.

The Best Mortising Attachment Kits on Amazon

Grizzly H7789 - The Trusted Kit

Grizzly Industrial H7789 Mortising Attachment Kit

This is the kit Grizzly uses in their own drill-press-to-mortising-machine instructional content, and it’s the standard recommendation in the hobbyist woodworking community. The H7789 includes:

Cast-iron chisel holder and fence
Hold-down assembly with three hold-down rods
Quill alignment pin
Four mortising chisels: 1/4”, 5/16”, 3/8”, 1/2”
Six bushings (three two-piece, three split) covering seven quill housing diameters
Carrying case

The cast-iron construction matters. Stamped-steel chisel holders flex under plunging load and cause chisel breakage. Cast iron doesn’t. The fence is adjustable for workpiece positioning and the hold-downs keep the stock from lifting on retract.

Pros:

Cast-iron holder stays rigid under load
Covers virtually every quill diameter you’ll encounter
Four chisels in one kit - you’re not ordering separately
Grizzly’s support documentation is thorough

Cons:

Alignment takes patience - the quill alignment pin procedure needs to be done correctly or your first mortise will be angled
Not for machines with sub-1.57” quill housings (small benchtop presses)
1/4” chisel is prone to snapping in hard maple if you rush the plunge

Shop Fox / Woodstock D4031 - Same DNA, Same Kit

Woodstock D4031 Mortising Attachment Kit

Shop Fox (the Woodstock brand) and Grizzly share ownership and manufacturing. The D4031 is functionally identical to the H7789 - same bushing range, same four chisel sizes, same cast-iron holder, same fence and hold-down system. The carrying case is identical.

If you find one of these in stock and the other isn’t, order whichever is available. There is no meaningful quality difference between them.

The Chisel and Bit Side of the Equation

Fisch Mortise Bit Chisel Set - Hollow Square Hole Drill Bits for Wood

CMT 543.127.51 Mortise Chisel and Bit Set, 1/2 inch

CMT 543.190.51 Mortise Chisel and Bit Set, 3/4 inch

Which Drill Presses Are the Best Hosts

The Grizzly G0485 is a 17” floor-standing drill press with sufficient quill travel, a solid column, a heavy cast-iron table, and enough motor (3/4 HP) to drive a 1/2” chisel through hard maple without bogging. The Shop Fox W1680 and M1039 are comparable floor-standing presses from the same parent company. The JET JDP-17M is the mortising-specific variant in the JET floor-press lineup. The Delta 11-990 is a dedicated benchtop mortising machine - not a drill press at all, but worth knowing about if your use case is primarily mortising.

FAQ

Can I use a mortising attachment on a benchtop drill press? Yes, but with conditions. The machine needs at least a 1/2 HP induction motor, solid cast-iron table, and a quill housing diameter that matches the available bushings (1.57”-2.95”). Small 10” swing benchtop presses generally don’t meet these requirements.

What is the G9716 adapter? The Grizzly G9716 is a column collar adapter for Grizzly-specific machines where the standard bushing range doesn’t quite match.

What size mortising chisel should I start with? Start with 3/8”. It’s the most common size for standard furniture joinery and forgiving of alignment errors compared to 1/4”.

Why does my mortising chisel keep breaking? Almost always wrong chisel-to-bit clearance or plunge speed too fast. Plunge steadily and hone the chisel before first use.

What’s the difference between a mortising bit and a regular drill bit? A mortising bit is sized to run inside a specific chisel size with proper clearance on all four sides.

References

Grizzly H7789 product page: grizzly.com
Shop Fox D4031 manual: grizzly.com/manuals
Fisch Tools product information: fisch-tools.com
JET JDP-17M specifications: jettools.com