By Finlay Connolly

The Short Answer

For most home shops, start with a shop-made jig. It costs under $20 in plywood and hardware, takes about an hour to build, and cuts excellent box joints once you’ve dialed in the fit with a test cut. Buy a commercial jig if you cut joints often, want to change finger sizes without building a new jig, or want fine adjustment in thousandths of an inch. Current options run from about $100 for a flat-pack kit to roughly $215 to $280 for the INCRA I-Box. Whichever way you go, you’ll need a stacked dado set, and you need to confirm that your saw can run one safely.

Finger Joint or Box Joint?

Woodworkers often use the two names interchangeably for the square, interlocking corner joint used on drawers and boxes, and that is the joint this guide covers. Strictly speaking, some references reserve “finger joint” for the end-to-end splice used to make long boards from short pieces, the kind you see in paint-grade trim, and use “box joint” for the right-angle corner version. If you want to splice boards end to end, you are after a different joint that is usually cut with a router bit or shaper cutter, not a table saw jig.

How a Finger Joint Jig Works

Every table saw jig for this joint works on the same principle. The workpiece stands on end against a fence attached to your miter gauge or a sled, and a dado stack cuts a notch across the end. A small key, or pin, sits on the jig exactly one cutter width away from the blade. After each cut you drop the notch you just made over the key, which positions the board for the next notch, so the spacing is identical every time.

Two boards cut this way mesh like the teeth of a comb. You start the first board with its edge against the key, and you start the mating board offset by one finger, using the first pin of the first board as a spacer. The result is a corner with a large amount of long-grain glue surface, which is why the joint is popular for drawers, boxes and casework.

Before You Start: What Your Saw Has to Allow

A Dado Stack Means Guard Off

The notches are non-through cuts made with a dado stack, so the blade guard has to come off. That raises the risk of blade contact, which is why clamping the workpiece and any built-in guard on the jig matter. Keep your hands well clear of the blade, hold the workpiece tight against the fence (and clamp it where you can), and move the rip fence out of the way. The Shop Fox manuals specifically warn against using the fence together with the miter gauge.

Check Your Saw’s Dado Limits

Read your manual for the maximum dado diameter and width before you buy a stack. Shop Fox’s W1888 is rated for dado sets up to 8 inches in diameter and 13/16 inch wide, with a dado insert designed for 8 inch blades only, while the W1837 accepts sets up to 10 inches. Our Shop Fox W1888 vs W1837 comparison covers those differences in detail.

On a SawStop, the manufacturer says the dado brake cartridge must be used for dado cuts, because it has a larger brake pawl designed to stop multiple blades, and you also need a zero-clearance insert for the stack. The cartridge is designed for standard 8 inch stacked sets, and wobble-type sets are not recommended.

Check Your Miter Slot

Most commercial jigs ride in a standard 3/4 inch by 3/8 inch miter slot, which is what INCRA lists for the I-Box. The KM Tools jig uses an expandable plywood runner meant to fit different saws. If your saw has an unusual slot, confirm compatibility before you order.

Build or Buy?

Option	Typical cost	What you get	Best for
Shop-made jig	Under $20 in materials	A plywood or MDF fence and a hardwood key riding on your miter gauge or a sled. Sized to one finger width, and you can build in a small sideways adjustment to fine-tune the fit.	Occasional boxes and drawers at a fixed finger size
KM Tools Universal Box Joint Jig	$99.99	Flat-pack kit you assemble and sand. Four key sizes (1/4″, 3/8″, 1/2″, 5/8″), a micro-adjust knob, MDF zero-clearance fences, and an expandable plywood miter-slot runner. Designed for a table saw with a dado stack.	A low-cost, ready-made jig for the common finger sizes
POWERTEC 71759	About $140 to $150	Works on table saws and router tables. Includes an MDF sub fence, a safety blade guard, a clamp guard, stop plates and an adjustment knob for fine tuning.	A budget adjustable jig with built-in guarding
INCRA I-Box	About $215 to $280	Pin widths from 1/8″ to 3/4″ in stock 1/4″ to 7/8″ thick. Micro-adjustable fit, front and rear blade guards, reversible design, and decorative joint options. Fits 3/4″ x 3/8″ miter slots. Made in the USA.	Frequent joinery, varied finger widths, and decorative joints

Prices are recent retailer and manufacturer listings and vary by seller, so check current pricing before you buy. We have not tested these jigs hands-on. Descriptions are based on manufacturer specifications and published reviews.

A shop-made jig is a good fit if you build the occasional box or drawer at one or two finger sizes. Woodsmith’s author usually makes a fresh jig for each project rather than adjusting one to suit different finger widths, which tells you how cheap and quick they are to build. A commercial jig makes more sense when you cut joints often, change sizes frequently, or need to repeat a fit exactly. The INCRA I-Box adds decorative joint options and lists cutting two or more boards at once up to 1 inch total thickness, though reviewers have noted a learning curve when setting it up. The KM Tools and POWERTEC jigs both aim at the middle ground, and we found less independent testing of the POWERTEC than of the INCRA.

Building a Simple Shop-Made Jig

This approach follows the methods published by Woodsmith and Family Handyman. Use flat, straight material for the fences.

1. Choose your finger width and set up the stack. Match the stack to the finger width you want, for example 1/4 inch pins for 1/2 inch stock. Measure the assembled stack with calipers. Do not trust the markings on the chippers.
2. Make the jig body. Fasten a flat plywood or MDF front fence to a rear fence or sled base that mounts to your miter gauge. Drill the screw holes that attach the front fence slightly oversize, so you can nudge it sideways a hair to fine-tune the spacing. This is Woodsmith’s approach, and it saves a lot of test-cut time.
3. Cut the key slot. Make a cut through the front fence with the dado stack. Mill a hardwood key to fit the slot snugly, but not so tight you have to force it. Make the key long enough that you can trim a piece off to use as a spacer.
4. Set the spacing. Slide the jig up to the blade, place the spacer between the outside teeth of the blade and the key, and lock the front fence in that position.
5. Make test cuts on scrap. Use scrap the same thickness and width as your project parts. Cut the first notch with the edge of the board against the key, place each freshly cut notch over the key for the next cut, then flip the board and use its first pin as a spacer when starting the mating piece. Test-fit the pair.
6. Tune the fit. If the joint is loose, the pins are too small, so move the key farther from the blade. If it is too tight, move the key closer. Aim for a fit that seats with a light tap, not one that needs to be forced.
7. Cut the real parts. Set the blade height a hair above the thickness of the mating board so the fingers stand slightly proud, and sand or plane them flush after glue-up. Hold each board tight against the fence with its end flat on the table, mark your starting edges so every board is cut from the same edge, and stop after each matched set to check that the jig has not crept.

Choosing Finger Width and Board Width

Finger width is largely a matter of looks and strength. A common rule of thumb is to make it roughly equal to the stock thickness, for example 1/2 inch fingers on 1/2 inch drawer stock, and many woodworkers go as narrow as half the thickness. Popular sizes are 1/4, 3/8 and 1/2 inch, and thinner fingers add glue area.

For a symmetrical joint, the board width should be an odd multiple of the finger width, so each board starts and ends with a pin or a socket. With 1/2 inch fingers, a 3-1/2 inch board gives seven segments, and a 6-1/2 inch board gives thirteen. A 4 inch board gives eight, an even number, so you would end up with a pin on one edge and a socket on the other. In that case, resize the board or pick a different finger width, and avoid ending with a thin sliver of a finger at an edge, because it will be weak.

Blades: Stacked Dado, Flat-Top Grind and Single Blades

A stacked dado set is the usual choice because you can adjust its width with shims and chippers. Most stacks have beveled outer teeth that reduce tearout but leave small ridges, sometimes called bat ears, at the edges of the notch, and only a flat-top grind leaves a truly flat bottom. The ridges are often minor and can be cleaned up with a chisel, and they matter more on a visible joint than on a drawer box. If the look matters to you, consider flat-top outer blades or a dedicated box joint set. Freud has sold one for 1/4 and 3/8 inch fingers, although owners report that its kerfs are not exactly 1/4 or 3/8 inch, so test and adjust.

You can also cut the joint with a single flat-top blade, but you either need a jig built to that blade’s kerf (1/8 inch for a standard blade) or several nibbling passes per notch with a micro-positioning jig. Wobble-type dado sets are best avoided, both because they tend to leave uneven bottoms and because they are not recommended for SawStop’s brake cartridge.

Fixing Common Problems

Symptom	Likely cause	Fix
Joint is too loose	Pins are too small	Move the key slightly farther from the blade to widen the pins
Joint is too tight or will not seat	Pins are too large	Move the key slightly closer to the blade to narrow the pins
Fingers sit below the surface	Blade too low, or the workpiece was not flat on the table	Raise the blade a hair and keep every end flat on the table. Cut fingers slightly proud and sand them flush after glue-up.
Ragged edges on the back side of the cut	Tearout at the blade’s exit point	Use a backing fence or sacrificial backer, a zero-clearance insert, a sharp blade and a steady feed
Small ridges at the edges of the notches	Beveled outer teeth on the dado set	Use flat-top-grind outer blades or a dedicated box joint set, or clean up the notches with a chisel
Fit changes partway through the job	The jig or key has crept out of position	Stop after each matched set and test-fit, as Woodsmith advises
Uneven spacing or a fit you cannot dial in	Stack width does not match the key	Measure the stack with calipers instead of trusting the chipper markings, then re-shim

Common Mistakes People Make

• Trusting the nominal width of the dado stack instead of measuring it, then wondering why the key never fits
• Skipping test cuts on scrap of the same thickness as the project parts
• Not holding the workpiece tight against the fence with its end flat on the table
• Cutting without a backing fence or zero-clearance insert, which leaves ragged exit edges
• Buying a dado set before checking the maximum diameter and width the saw allows
• Picking a finger width that leaves a tiny sliver at the board’s edge
• Forgetting to re-check the fit after each matched set, so a drifting jig ruins a whole batch
• Leaving the rip fence in place while using the miter gauge and jig
• Assembling too slowly, since glue starts to tack up quickly across all those mating surfaces

Frequently Asked Questions

What is the best finger joint jig for a table saw?

It depends on how often you cut joints. A shop-made jig is the best value for occasional use. The KM Tools kit is a low-cost ready-made option for common finger sizes, and the INCRA I-Box is the more capable choice if you cut a lot of joints in varied widths or want decorative options.

Do I need a dado stack?

In practice, yes. A stack lets you cut each notch in one pass and adjust its width precisely. A single blade can do the job but requires more passes or a jig matched to the blade’s kerf.

Are finger joints as strong as dovetails?

A glued finger joint has a large amount of long-grain glue surface, so it is strong, but it lacks the mechanical interlock of a dovetail and relies on the glue to resist pulling apart. For most boxes and drawers, that is plenty.

Can I cut two or more boards at once?

Yes, some jigs are designed for it. INCRA lists cutting two or more pieces at a time up to 1 inch total thickness, and many woodworkers clamp boards together for shop-made jigs. It only works if your setup is accurate, so test with scrap first.

Do I need a zero-clearance insert?

It is a good idea on any saw because it supports the wood fibers on both sides of the stack and keeps notch edges crisp. On a SawStop, it is required with the dado brake cartridge.

Can I use a finger joint jig on a hybrid or contractor saw?

Yes, as long as the saw can safely run the dado stack you want to use. Check the manual for the maximum diameter and width, and confirm your miter slot size before buying a commercial jig.

Bottom Line

A finger joint jig is one of the most useful additions to a table saw shop, and you don’t need to spend much to get good results. Build a simple shop-made jig if you cut joints occasionally, and use the fit-tuning steps above to get a joint that seats with a light tap. Step up to the KM Tools, POWERTEC or INCRA jig when you cut joints often or want more adjustability. Whatever you choose, measure your dado stack, check your saw’s dado limits, make test cuts on scrap, and keep your hands well clear of the blade.

Sources

Setup, spacing and fitting guidance follows published methods from these sources. Manufacturer details come from each company’s own pages and manuals.

Woodsmith: Perfect-Fitting Finger Joints

Family Handyman: How to Make a Box Joint Jig

INCRA I-Box Jig

KM Tools Universal Box Joint Jig

SawStop: Can I make dado cuts?

Shop Fox W1888 owner’s manual