Mortising Attachment for Drill Press Harbor Freight: Compatibility and Setup Guide

Harbor Freight presses are where a lot of woodworkers start, so it is natural to ask whether a mortising attachment will turn one into a square-hole machine. It can, sometimes, but the honest answer hinges on one thing people skip: mortising attachments are model-specific, and they clamp to your press’s quill and column. Whether one fits your Harbor Freight press depends on those dimensions, not on the store you bought it from. Here is how to check compatibility and set the attachment up so it cuts clean mortises.

A mortising attachment for a drill press holds a hollow square chisel while an auger bit spins inside it, so the press cuts square holes for mortises. It clamps to the quill and column, so fit depends on those dimensions. A representative kit like the Grizzly H7789 ships with a column collar and a G9716 adapter and lists the specific presses it fits.

Short answer: a mortising attachment works on a Harbor Freight press only if the attachment’s collar and adapter fit that press’s quill and column diameters. Measure those and check the attachment’s fitment, since kits like the H7789 list set compatible models.

Compatibility is about the quill and column

A mortising attachment does its job by clamping to the drill press quill and around the column, holding the hollow chisel square to the table. That means the deciding numbers are your press’s quill diameter and column diameter, and whether the attachment’s collar and adapter match them. A kit like the Grizzly H7789 spells out its fit: it includes a column collar and a G9716 adapter and is specified for a defined list of presses, the Grizzly G0485, G0491, G7943, G7944, G7947, and G7948, the Shop Fox W1680 and M1039, the Delta 11-990 and 17-900, and the JET JDP-17M.

Your Harbor Freight press is not on that list, so the practical test is dimensional: measure your quill and column and compare them to an attachment’s stated fitment. If they match a kit’s collar and adapter, it can work; if not, it will not clamp correctly.

What the attachment does

The attachment holds the hollow square chisel fixed and aligned while the auger bit spins inside it, clearing waste as the chisel squares the corners. You feed down with the press’s lever, and each plunge cuts a square hole; overlapping plunges make a mortise. Without the attachment, there is nothing to hold the chisel, so the chisel-and-bit set cannot be used by chucking the bit alone.

Check before buying

• Quill diameter. Must match the attachment’s clamp.
• Column diameter. Must match the collar, as the H7789 uses a specific column collar.
• Chisel and bit sizes. Match the hollow chisel and auger to the attachment.
• Stability. The press should be rigid enough to feed the chisel without flexing.

Attachment on a light press versus a dedicated mortiser

Against a dedicated mortising machine, a mortising attachment on a light Harbor Freight press wins on using a tool you own and loses on leverage, rigidity, and ease over many mortises. A light press may flex under the force a chisel needs, so take lighter plunges. For occasional mortises on a compatible press, the attachment works; for frequent mortising, a dedicated machine is far easier. You can compare a drill press mortising attachment with mortising chisels and bits.

Setting it up

1. Measure your press’s quill and column and confirm an attachment fits those dimensions.
2. Clamp the attachment to the quill and fit its collar to the column.
3. Install the hollow chisel and auger with the specified small gap, squared to the fence.
4. Clamp the stock firmly against the fence so it cannot lift on the up-stroke.
5. Feed down in light plunges, clear chips, wear eye protection, and keep clear of the chuck, per CCOHS.

Who should read this

If your Harbor Freight press’s quill and column match an available attachment, you can cut mortises with it, take lighter plunges if the press is light. If nothing fits, or you cut mortises often, a dedicated mortiser is the better tool.

Bottom line

A mortising attachment can turn a Harbor Freight drill press into a square-hole cutter, but only if the attachment’s collar and adapter fit your press’s quill and column. Measure those dimensions and check fitment against a kit like the Grizzly H7789. Clamp the stock, square the chisel, and feed in light plunges, and a compatible press cuts clean mortises.

• Fit depends on your press’s quill and column, not the store it came from.
• Attachments are model-specific; kits like the H7789 list set compatible presses.
• Clamp the stock, square the chisel, and take lighter plunges on a light press.

FAQ

Will a mortising attachment fit my Harbor Freight drill press? Only if the attachment’s collar and adapter match your press’s quill and column diameters. Measure those and check the attachment’s fitment.

Is there a Harbor Freight-specific mortising attachment? What matters is dimensional fit, not brand. Kits like the Grizzly H7789 list set models; compare their collar and adapter sizes to your press.

Can I just chuck a mortise bit without the attachment? No. The hollow chisel must be held by the attachment. The bit alone cannot cut square corners and is unsafe.

Why does my stock lift on the up-stroke? The chisel can grab. Clamp the stock firmly against the fence so it cannot lift with the chisel.

Will a light press handle mortising? A light press may flex under the chisel’s force, so take lighter plunges. A rigid press or a dedicated mortiser handles it better.

What sizes of chisel do I need? Match the hollow chisel and auger bit to the attachment and to your mortise width, keeping the specified small gap between chisel and bit.

References

• Grizzly H7789 Mortising Attachment Kit: https://www.grizzly.com/products/grizzly-mortising-attachment-kit-for-drill-presses/h7789
• TEKTON 4-Inch Drill Press Vise Manual: https://media.tekton.com/manuals/manual_53994.pdf
• CCOHS, Metalworking Machines - Drill Presses: https://www.ccohs.ca/oshanswers/safety_haz/metalworking/drillpresses.html