How a hollow-chisel mortiser works, and how the chisel and auger are set, is explained in the mortiser guide. This guide is about reading a benchtop machine's data sheet against the mortises you plan to cut. If you are still choosing between a benchtop, a floor machine or another kind, start with how to choose a mortiser.
Match the machine to the work
| Work | Figure that decides it | What to check |
|---|---|---|
| Chair and table rails | Chisel range and depth | Chisels up to the mortise width you use; maximum mortising depth at least the tenon length |
| Mortises in thick legs | Stock thickness and fence distance | Maximum stock thickness, with any column extension; fence-to-chisel distance for mortises set back from the face |
| Wide parts, such as bed rails or panels | Stock width and column distance | Maximum stock width; column-to-chisel distance |
| Many identical mortises | Fence, hold-down and depth stop | A fence that adjusts finely and locks; a hold-down; a positive depth stop |
Planning guidance from what the manuals state. Not a ranking.
Two benchtop machines by their data sheets
| Figure | Grizzly G0645 | Grizzly T33127 |
|---|---|---|
| Motor | 1/2 HP, 1725 rpm, 110 V, 6 A | 1/2 HP, 1720 rpm, 120 V, 3.4 A |
| Chisels | 1/4, 5/16, 3/8, 1/2 in | Up to 1/2 in; 3/4 in collar |
| Chisel travel | 4-5/8 in | 4-7/8 in |
| Maximum mortising depth | 3 in | 3 in |
| Maximum stock | 8-1/2 in wide; 6 in thick with the column extension | 13-3/8 in wide; 4 in thick |
| Column to chisel | 5 in | 5-1/8 in |
| Fence to chisel centre | 4 in | Not listed on the data sheet |
| Table | 12-1/4 × 10-1/2 in, cast iron | 13-1/2 × 6 in, wood; cast-iron fence |
| Weight | 70 lb | 60 lb |
Grizzly's figures for its own machines, from their manuals. 'Not listed' means the figure is not on that data sheet, not that it is zero. Not a ranking.
Specifications to check
| Specification | Why it matters | How to check |
|---|---|---|
| Chisel range and collar | Sets the widest mortise and which chisels fit | Sizes listed, and the collar or shank size; the maker's chisel and auger dimensions if buying others |
| Travel and maximum depth | Sets the deepest single hole | Both figures; depth is the one that limits the tenon |
| Stock capacity | Whether the part fits under the head and against the fence | Width, thickness, and what an extension or rotated column adds |
| Fence-to-chisel distance | How far from the face a mortise can sit | The figure, and how finely the fence adjusts |
| Hold-down and depth stop | Stops the work lifting with the chisel; repeats depth | Both present and adjustable |
| Supply and mounting | The outlet and the bench it needs | Voltage, amps and circuit from the manual; a bench that takes the weight |
What each figure decides; read every one from the machine's own manual. Not a ranking.
What a benchtop mortiser cannot do
- Wide chisels. Both machines here stop at 1/2 in. Larger chisels are a floor machine's job — Grizzly's G0448 has a 1-1/2 HP motor and a 6-1/4 in stroke.
- Angled mortises. Neither data sheet lists a tilting head; the G0448's tilts 30° each way.
- Round-ended or loose-tenon mortises. A hollow chisel cuts square-cornered holes; slot mortisers are compared in how to choose a mortiser.
- Heavy timber. Mortises in timber-frame sizes need a chain mortiser, a different tool for different work.
Safety— Power off to change chisels
Grizzly has its mortisers disconnected from power before a chisel is fitted, the chisel handled with gloves or a towel, the hold-down set just above the work, and safety glasses and a respirator worn. Its benchtop manual asks for a workbench that carries the machine and the work. See woodworking safety rules.
Before buying a benchtop mortiser
- Widest and deepest mortise you plan to cut, written down
- Chisel range and collar size cover it
- Stock width and thickness of your largest part fit
- Fence-to-chisel distance suits your mortise positions
- Supply matches an outlet you have; bench can carry it
- Replacement chisels and augers of the right dimensions can be found
Cutting the tenon to match is covered in the tenon jig guide; the other joinery tools are mapped in the pocket hole guide.
Sources
Specification-based: figures are Grizzly's for its own machines, from their manuals, shown to compare what each data sheet states; the G0448 is a floor machine included only to show where a benchtop's limits lie. Other makers measure some capacities differently, so compare like with like from each manual. Nothing was tested and none is ranked.
- 1.
Model G0645 Benchtop Mortising Machine, Owner's Manual. Grizzly Industrial, 2010.
Used for: Benchtop mortiser figures: 1/2 HP at 1725 rpm, 110 V, 6 A, a 15 A minimum circuit; 70 lb; chisels of 1/4, 5/16, 3/8 and 1/2 in; 4-5/8 in chisel travel; 3 in maximum mortising depth; stock up to 8-1/2 in wide and, with the 1-3/4 in column extension, 6 in thick; 5 in column to chisel and 4 in fence to chisel centre; a 12-1/4 × 10-1/2 in cast-iron table; a column that rotates for taller work; the bit 1/16 to 3/16 in beyond the chisel; a workbench strong enough for the machine and work.
- 2.
Model T33127 Benchtop Hollow-Chisel Mortiser, Owner's Manual. Grizzly Industrial, 2024.
Used for: Benchtop mortiser figures: 1/2 HP at 1720 rpm, 120 V, 3.4 A, a 15 A minimum circuit; 60 lb; a 1/2 in maximum chisel with a 3/4 in collar; 4-7/8 in chisel travel; 3 in maximum mortising depth; stock up to 13-3/8 in wide and 4 in thick; 5-1/8 in column to chisel; a 13-1/2 × 6 in wooden table; a spring-tensioned cast-iron fence with micro-adjustment; the auger 1/16 in beyond the chisel; its chisel and auger pairs by size.
- 3.
Model G0448 Mortising Machine, Owner's Manual. Grizzly Industrial.
Used for: A floor mortiser for comparison: 1-1/2 HP, 6-1/4 in stroke, a head that tilts 30° each way, 332 lb, bolted to the floor.
About this buying guide
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