What's inside
- At a glance: the five best options
- 1. Delta 17-924: best overall
- 2. Grizzly H7789: best value
- 3. Shop Fox D2056: best for fence rigidity
- 4. Generic four-chisel cast-metal kit: best low-cost option
- 5. Generic eight-piece kit: best for larger mortises
- Compatibility: measure the quill before buying
- Decision matrix
- Setup steps that determine whether the mortise is square
- Ownership costs and common failures
- Final recommendation
- Related Guides
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The Delta 17-924 is the best all-around drill press mortising attachment, while the Grizzly H7789 is the better value for occasional work and the Shop Fox D2056 is the safer choice when fence rigidity matters most. A mortising attachment turns a drill press into a square-hole machine by holding a hollow chisel around a rotating bit, but the result depends less on the advertised chisel range than on quill-collar fit, spindle clearance, and how firmly the fence stays put.
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At a glance: the five best options
| Attachment | Chisel sizes typically included | Quill-collar range | Fence and body | Best for | Typical 2026 market range |
|---|---|---|---|---|---|
| Delta 17-924 | 1/4, 5/16, 3/8, 1/2 in | Approximately 2 to 2-1/2 in, depending on collar set | Cast-metal bracket; adjustable work stop and fence | General furniture and cabinet work | $90-$160 when available |
| Grizzly H7789 | 1/4, 5/16, 3/8, 1/2 in | Approximately 1-5/8 to 2-1/2 in with supplied hardware | Steel attachment plate; sliding fence | Budget-conscious occasional use | $70-$120 |
| Shop Fox D2056 | 1/4, 5/16, 3/8, 1/2 in | Approximately 1-5/8 to 2-1/2 in | Rigid steel bracket; broad table-side support | Frequent shop use and longer workpieces | $100-$170 |
| Generic four-chisel cast-metal kit | 1/4, 5/16, 3/8, 1/2 in | Usually 1-1/2 to 2-1/2 in; measure before buying | Varies widely; often narrow stamped fence | Lowest initial cost | $45-$90 |
| Generic eight-piece mortising kit | 1/4, 5/16, 3/8, 1/2, 5/8, 3/4 in plus metric equivalents | Often 1-1/2 to 2-1/2 in | Usually cast bracket with longer fence | Large joinery and mixed-size work | $80-$150 |
Sizes and collar hardware can change between production runs, particularly for older Delta and imported kits. Treat the table as a buying guide, then compare the current manual and included collars with your drill press before ordering.
1. Delta 17-924: best overall
The Delta 17-924 remains the most balanced mortising attachment for drill presses that have a conventional quill collar. Its useful four-chisel set covers the sizes used for most table legs, rails, face frames, and small timber projects without filling the shop with rarely used large chisels.
Its main advantage is adjustability. The attachment lets you align the hollow chisel to the drill chuck and position the fence close enough to support narrow stock. That matters because a mortising attachment can cut a square hole while still producing a mortise that is not square to the workpiece if the fence flexes or the stock lifts.
Choose it for a Delta, Jet, older Craftsman, or similar floor-standing drill press when the quill collar is within the supplied range. It is less attractive for compact benchtop machines with short quills, exposed return springs, or a collar that is too small for the bracket.
2. Grizzly H7789: best value
The Grizzly H7789 is a sensible mortising attachment for a drill press used a few times each month. Its 1/4- to 1/2-inch chisel range covers standard cabinet and furniture joinery, and replacement chisels in those sizes are easy to find.
The compromise is fence stiffness. A narrow fence is adequate for short mortises in 3/4-inch stock, but it can shift when a long board is pushed against it. Tighten both fence fasteners evenly and add a separate auxiliary fence if you routinely work with tall or heavy pieces. That inexpensive improvement is more useful than buying a kit with extra chisels you rarely use.
This is the best choice for a first mortise attachment when your drill press has a flat, accessible quill collar and a table that can be locked securely.
3. Shop Fox D2056: best for fence rigidity
The Shop Fox D2056 is the strongest choice among these attachment-style options when maintaining a square reference is the priority. Its steel bracket and broad support arrangement reduce the tendency of the fence to rotate under side pressure.
It still cannot compensate for a loose drill-press table, a bent column, or a quill with excessive play. Before blaming the attachment, lock the table height and rotation, lower the quill, and push the chuck sideways. Noticeable movement will be transferred directly into the mortise.
The included 1/4-, 5/16-, 3/8-, and 1/2-inch sizes make it a practical everyday set. For a shop that cuts repeated mortises in hardwood, its extra rigidity is more valuable than an eight-piece kit with a flexible fence.
4. Generic four-chisel cast-metal kit: best low-cost option
A generic four-chisel mortising attachment is worthwhile when the purchase price must stay below about $90 and the drill press is used for small projects. The typical set includes the same four useful imperial sizes as the branded kits.
Quality varies sharply. Inspect the chisel holders for burrs, check that the drill bits rotate freely inside the chisels, and reject any kit whose fence has visible play after tightening. Some kits use a collar that fits only a narrow band of drill presses, so “universal” should not be interpreted as “fits every drill press.”
For occasional use, this type can cut clean mortises after careful setup. It is not the best choice for production work, deep hardwood mortises, or situations where replacing a worn bracket would be difficult.
5. Generic eight-piece kit: best for larger mortises
An eight-piece mortising attachment is the practical pick when your work includes 5/8- and 3/4-inch mortises as well as ordinary cabinet sizes. It gives more flexibility for bed hardware, large table construction, and heavier frame-and-panel work.
The extra capacity comes with two warnings. First, a large chisel creates much more resistance; use a slow drill-press speed and take shallow plunges. Second, a large chisel magnifies fence movement. Buy this style only when its bracket and fence are visibly more substantial than the four-chisel alternatives.
Compatibility: measure the quill before buying
A mortising attachment for a drill press normally clamps around the quill or quill collar; it does not attach to the chuck alone. Measure the outside diameter of the usable collar, the available vertical length, and the distance from the bottom of the collar to the chuck or spindle nose.
- Collar diameter: it must fall inside the attachment’s stated range without improvised shims.
- Vertical clearance: the bracket must sit high enough that the hollow chisel does not bottom out before the drill bit reaches its cutting depth.
- Chuck clearance: the chisel holder must not strike the chuck, chuck key, or return-spring housing.
- Table travel: allow space for the workpiece, fence, and depth stop at the intended mortise location.
Most full-size floor drill presses are easier candidates than small benchtop models. A hand drill press attachment is a different category: handheld drill guides generally cannot provide the fixed quill alignment or fence rigidity needed for accurate hollow-chisel mortising. Do not confuse a guide for a hand drill with a mortising attachment designed for a drill press.
Decision matrix
| Your situation | Recommended choice | Why |
|---|---|---|
| First attachment, occasional projects, limited budget | Grizzly H7789 or a carefully checked generic four-chisel kit | Useful sizes without paying for infrequently used large chisels |
| Cabinetmaking and furniture several times a month | Delta 17-924 | Balanced size range and adjustability |
| Long boards, hardwood, or repeated mortises | Shop Fox D2056 | Fence rigidity is more important than extra chisel count |
| Large timber joinery and 5/8- to 3/4-inch mortises | Eight-piece kit with a reinforced fence | Broader capacity, provided the drill press has enough power and clearance |
| Compact benchtop drill press | Buy only after a collar-and-clearance check | Short quill travel and small collars are common deal-breakers |
Setup steps that determine whether the mortise is square
- Clean the quill and bracket. Oil, sawdust, or a burr can tilt the attachment before tightening.
- Install the bit with slight clearance. The bit should rotate freely inside the chisel, with the chisel held slightly above the bit’s cutting tips during initial alignment.
- Align the chisel faces. Set the flat faces parallel and perpendicular to the fence. A small twist produces angled mortise walls.
- Lock every movable part. Secure the drill-press table, attachment bracket, fence, and depth stop.
- Use a backing board. It reduces breakout when the bit exits and keeps the workpiece supported.
- Plunge in short increments. Clear chips frequently, especially in hardwood. For a 1/2-inch chisel, multiple 1/8- to 1/4-inch plunges are safer than forcing the full depth at once.
- Test scrap first. Check width, depth, squareness, and fit before cutting the actual rail or leg.
Ownership costs and common failures
The drill bits usually wear before the hollow chisels, particularly when chips are not cleared. A dull bit makes the operator push harder, increasing heat and side load. Chisel corners eventually round over, while the first signs of a failing bracket are usually fence movement, elongated mounting holes, or a collar that no longer clamps evenly.
As a simple cost check, a $120 attachment used for 30 projects costs $4 per project before replacement bits and chisels. If you expect fewer than ten uses, a basic four-chisel kit is financially sensible; if you expect years of repeated work, paying more for a rigid bracket and readily available replacement chisels is usually the better ownership decision.
Clean chips from the chisel flutes after every session, wipe the bits dry, and apply a light rust-preventive film to carbon-steel components. Never run the attachment at the same speed used for a small twist drill. Large hollow chisels need slower speeds, firm clamping, and patience.
Final recommendation
Choose the Delta 17-924 for the best balance of sizes, adjustment, and everyday usefulness. Choose the Shop Fox D2056 when a rigid fence and repeatable alignment matter more than the lowest price. The Grizzly H7789 is the sensible value pick, while generic kits make sense only after confirming the quill collar, clearance, and fence quality. For a drill press with a mortise attachment to cut truly square mortises, fit and rigidity matter more than the number of chisels printed on the box.