The four jobs of any jig
- Register. The work goes against a known face or stop — a fence, a key, a guide block — so its position does not depend on a pencil line.
- Hold. A clamp, toggle or hold-down keeps it there while the tool cuts. Kreg's first rule for its pocket hole jigs is that the jig and the work are secured, never held by hand.
- Guide. A fence, guide bush, runner or key steers the cutter or the work along a fixed path.
- Repeat. Because the first three do not change between parts, the tenth cut matches the first. That is the point of a jig, and the reason a small error in its reference face repeats in every part.
Seen this way, a crosscut sled, a pocket hole jig and a dovetail template are the same idea applied to different cuts. It also explains the test every jig maker asks for: a cut in scrap of the same stock, checked before the real parts, because the jig only reproduces what its set-up gives.
Jig or fixture?
In engineering usage a fixture is often said to hold the work and a jig to guide the tool. Woodworkers rarely keep the two apart: a box joint jig holds and indexes the work, a dovetail jig holds the boards and guides the router, and both are called jigs. Treat the difference as a habit of speech, not a rule; what matters is which of the four jobs a device does and how well.
Which jig, and where it is explained
| Jig | What it registers and guides | Tool it works with |
|---|---|---|
| Pocket hole jig | The part's face against a guide block; a stepped bit at a set angle | Drill |
| Dowel jig | The board's edge or face; a bushing over the hole position | Drill |
| Dovetail jig | Both boards against stops; a template and guide bush | Router |
| Box joint jig | The board against a key; a fence on the miter gauge | Table saw or router table |
| Tenoning jig | The part upright against the jig's face; a bar in the miter slot | Table saw |
| Crosscut sled | The part against a fence square to the blade; runners in the miter slots | Table saw |
| Router template | A template edge followed by a bearing or guide bush | Router |
| T-track | Not a jig itself: a track that lets stops and clamps lock anywhere along a jig | Any jig built with it |
A summary of how each works; settings and dimensions are on each jig's own page, from its maker. Not a ranking.
- Pocket holes: the pocket hole guide.
- Dowels: the dowel jig guide.
- Dovetails: the dovetail jig guide.
- Box joints: the box joint jig guide, and two to build in box joint jig projects.
- Tenons: the tenon jig guide; mortises are cut by the machines in the mortiser guide.
- Track and stops: the T-track guide.
- Sleds and router templates: table saw sleds and router jigs and templates.
- Slots for biscuits are cut by a tool rather than a jig: see the biscuit joiner guide.
Bought or shop-made
| Point | Bought jig | Shop-made jig |
|---|---|---|
| Accuracy | Set by the maker; adjustable within its range | Set by your reference faces and fit |
| Instructions | A manual with settings and safety rules | Your own, or a cutter maker's (Freud's box joint jig is shop-made) |
| Adjustment | Often fine adjustment built in | Often re-made or re-set for each size |
| Fit to your tool | Made for standard slots and tools; check the fit | Made to fit your own tool |
General trade-offs, not a recommendation either way. Not a ranking.
A shop-made jig is only as good as the stock it is made from and the faces it registers on: flat, stable sheet material and square, straight edges. Measured plans for two shop-made box joint jigs are in box joint jig projects.
Safety with any jig
Safety— A jig must never take a guard's place
INCRA's rule for its box joint jig applies to every jig: never let it interfere with the tool's own safety equipment, and read the tool's manual first. Grizzly's tenoning jig manual requires a riving knife and has the blade guard put back whenever the jig comes off. Turn the power off and let the cutter stop before moving or adjusting any jig, clamp the work to the jig rather than holding it, and keep hands out of the cutter's path. See table saw safety and woodworking safety rules.
Before using a jig
- The tool's manual and the jig's manual both read
- Reference faces of the jig clean, flat and square
- Work clamped to the jig, not held by hand
- Guards and riving knife in place as the tool's manual requires
- Power off while setting or moving the jig
- Test cut in scrap of the same stock
Sources
This page explains what jigs have in common and points to the pages for each kind; settings and dimensions are on those pages, each from its maker. The jig and fixture distinction is described as usage, not as a definition any source sets. Safety rules are each maker's for its own jig.
- 1.
INCRA IBOX Owner's Manual. INCRA (Taylor Design Group), 2023.
Used for: A bought box joint jig's rules for use with another tool: read that tool's manual first, never let the jig interfere with the tool's own safety equipment, clamp the work to the jig with a handscrew before cutting, turn the power off and wait for the cutter to stop before moving the jig to a new setting, and use no wobble dado and no cutter under 1/8 in.
- 2.
Model H7583 Tenoning Jig, Owner's Manual. Grizzly Industrial, 2009.
Used for: A bought table saw jig whose maker requires a riving knife behind the blade and the blade guard re-installed whenever the jig is removed.
- 3.
Kreg Jig® Owner's Manual — Rocket™ Jig, K2000 Kreg Jig® and Mini Kreg Jig®. Kreg Tool Company (retailer-hosted copy).
Used for: Never hold a pocket hole jig by hand while drilling: the jig and the work are secured to something that cannot move.
- 4.
SBOX8 Box Joint Instructions. Freud (instruction sheet, distributor-hosted copy).
Used for: A shop-made box joint jig built to a cutter maker's instructions: a separate jig for each pin size, a hardwood key milled to fit a test slot, and test cuts before the real parts.
About this guide
Written by BenchRoot Editorial. How BenchRoot sources, checks and corrects its pages is set out in the Editorial Policy. If something here is wrong or unclear, the contact page explains how to tell us.