Two kinds of jig, two ways of cutting
| Type | What it cuts | Example | What it does not do |
|---|---|---|---|
| Table saw tenoning jig | Tenon cheeks, with the part held upright | Grizzly H7583 | Shoulders (cut afterwards without the jig); mortises |
| Router mortise and tenon jig | Mortises and tenons from templates | Leigh FMT | Work without a router suited to the jig |
| Router mortising jig or edge guide | Mortises only, with a plunge router | A fence or guide on the router | Tenons |
Each jig's own manual sets its capacities, bits and set-up. Industrial single- and double-end tenoners are production machines for factories, not workshop jigs, and are not covered. Not a ranking.
The joint itself — the names of its parts, proportions and fit — is explained in mortise and tenon joints. The mortise side can also be cut with a machine: hollow-chisel, chain and slot mortisers are in the mortiser guide.
The table saw tenoning jig
A tenoning jig rides in the saw's miter slot on a guide bar and holds the part upright against its face, square to the table, with a clamp. The blade is raised to the tenon's length; each pass cuts one cheek, and the jig's micro-adjustment moves the part sideways for the next. Grizzly's H7583 is built for a saw with a standard 3/4 in miter T-slot on the left of the blade, 3-3/4 to 6-3/4 in from the slot's centre to the blade, and it cuts cheeks only: the shoulders are cut afterwards, without the jig, with a crosscut blade.
- Fit the bar first. Grizzly has the guide bar adjusted so it slides in the slot without side play or tilt, and says never to remove the T-slot washer at the bar's ends, because it keeps the jig attached to the table if the work kicks back.
- Set the face parallel. The jig's side support is set parallel to the blade before any cut, then moved clear of it.
- Allow for the kerf. Each cheek line is aligned with the side of the blade that leaves the tenon, not the middle.
- Check the saw. The jig needs a saw whose slot and slot-to-blade distance fit it; read both manuals before buying one for a saw.
Safety— The table saw rules still apply
Grizzly requires a riving knife correctly installed behind the blade for every tenon cut, so the kerf cannot close on the blade and cause kickback; both of the jig's handles held, never one; and the saw disconnected from power before the jig, saw or work is installed or adjusted. Put the blade guard back on as soon as the jig comes off. General rules for the saw are in table saw safety.
Router jigs for mortises and tenons
A router mortise and tenon jig clamps the part and guides the router — through a template and guide bush, or along fences — so both halves of the joint are cut from the same references. Leigh's FMT is one: it routes mortises and matching tenons from templates, references every part from the same face, and aims for a fit of about 0.005 in loose — pushed together fairly easily, without falling apart. A simpler mortising jig, or an edge guide on a plunge router, cuts only the mortise; the tenon is then cut another way, on the saw or by hand. Router guidance in general is in router jigs and templates and the plunge router guide.
Tenon thickness is set from the joint
No source reviewed sets a universal ratio of tenon thickness to stock, and none is given here. Grizzly's advice for its jig is practical rather than fixed: where the mortised and tenoned parts are the same thickness, make the tenon the same thickness as each mortise wall; where the mortised part is thicker, make the tenon as thick as possible without leaving the walls too thin. It also leaves a little space at the bottom of the mortise for glue. Proportions and fit are covered with the joint in mortise and tenon joints and cutting it in how to cut basic joints.
The other joinery jigs — pocket hole, dowel, dovetail and box joint — are mapped in the pocket hole guide and the jig guide.
Before cutting tenons on a jig
- Jig fits the saw's slot and slot-to-blade distance
- Guide bar adjusted to slide without play; T-slot washer in place
- Jig face parallel to the blade
- Riving knife fitted; saw unplugged while setting up
- Test tenon cut in scrap and fitted to its mortise
- Shoulders planned as a separate cut
Sources
Table saw figures and rules are Grizzly's for its H7583 tenoning jig; other jigs have their own slot, distance and set-up requirements. Router jig figures are Leigh's for its FMT. Grizzly's guidance on tenon thickness is its own, for its jig, and BenchRoot gives no universal tenon-to-stock ratio, because no source reviewed sets one. Industrial single- and double-end tenoners are production machinery and are outside this guide.
- 1.
Model H7583 Tenoning Jig, Owner's Manual. Grizzly Industrial, 2009.
Used for: A tenoning jig for a table saw with a standard 3/4 in miter T-slot on the left of the blade, 3-3/4 to 6-3/4 in from slot centre to blade; for cheek cuts only, the shoulders cut afterwards without the jig using a crosscut blade; the guide bar adjusted to slide without play and its T-slot washer never removed, because it keeps the jig attached in a kickback; the side support set parallel to the blade; a riving knife always installed, the blade guard re-installed when the jig is removed, both handles held, and the saw disconnected before the jig, saw or work is adjusted; with mortise and tenon stock of the same thickness, the tenon made the same thickness as the mortise walls, and with a thicker mortised part, the tenon as thick as possible without thin walls; a little space left at the bottom of the mortise for glue.
- 2.
FMT Pro Frame Mortise & Tenon Jig User Guide. Leigh Tools (a Lee Valley Tools company).
Used for: A router jig that routes both mortise and tenon from templates, with every part referenced from the same face and a best fit of about 0.005 in loose.
About this guide
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