One of the first joinery cuts that new woodworkers try is the rabbet. A rabbet is simply an open-sided channel or recess along the edge or across the end of a board or panel. Easy to cut, it helps locate parts during assembly, and it provides more of a mechanical connection than does a butt joint.
I vaguely remember thinking, back when I was tackling my first home improvement projects, that with practice I'd "outgrow" rabbet joints. Well, of course, I'm still cutting rabbets, because woodworkers never "outgrow" them.
The most common form of rabbet joint is what I call the single rabbet joint. Only one of the mating parts is rabbeted. The cut is proportioned so its width matches the thickness of the mating board, yielding a flush fit.
The depth of the rabbet for this joint should be one-half to two-thirds its width. When assembled, the rabbet conceals the end grain of the mating board. The deeper the rabbet, the less end grain that will be exposed in the assembled joint.
In the double-rabbet joint, both the mating pieces are rabbeted. The rabbets don't have to be the same, but typically they are.
Either form works as a case joint. In casework, you often see rabbets used where the top and/or bottom join the sides (end-grain to end-grain) and where the back joins the assembled case (both end-to-end and end-to-long). In drawers, they're often used to join the front and sides.
Because end grain glues poorly, rabbet joints that involve it usually are fastened, either with brads or finish nails or with screws concealed under plugs. (OK, in utilitarian constructions, we don't sweat the concealment.)
Either form also makes a great right-angle edge joint. We see this in the case-side-and-back combination, but also in practical box-section constructions like hollow legs and pedestals. Long-grain joins long-grain in these structures; that glues well, and you have a terrific, strong joint.
A rabbet joinery variation very useful in casework — especially casework being built of sheet goods —is the rabbet-and-dado joint. This is a good rack-resistant joint that assembles easily because both boards are positively located. The dado or groove doesn't have to be big; often it's a single saw kerf, no deeper than one-third the board's thickness. Into it fits an offset tongue created on the mating board by the rabbet.
It is a good choice for plywood casework, because it's often difficult to scale a dado or groove to the inexact thickness of plywood. It's far easier to customize the width of a rabbet. So you cut a stock-width dado, then cut the mating rabbet to a custom dimension. An extra cutting operation is required, but the benefit — a big one — is a tight joint.
We don't necessarily think of the rabbet as a flat edge-to-edge joint, yet we all know of the shiplap joint.
A shiplap joint is formed by overlapping rabbets cut into opposite faces of adjoining boards. I'd call it a carpentry kind of thing, used in siding and natural wood paneling. But you'll see it in the backs of centuries-old cupboards and cabinets.
The joint allows individual boards to expand and contract seasonally without opening gaps between it and its neighbors. And that's the whole point of shiplaps. The rabbets are quickly cut, absolute precision is irrelevant; yet they serve a valid purpose.
In the same vein, we seldom perceive the rabbet as part of a frame joint. But almost all end-lap variations incorporate a rabbet cut in at least one of the mating parts. To make a half-lap joint, for example, we cut rabbets across the ends of the mating parts and nest them together. The joint mates face grain to face grain, an excellent gluing situation (even if the grains cross in the assembly), thus yielding a very strong frame joint.
There are two additional rabbet joint variations I want to mention.
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The mitered rabbet joint is one of those you see in drawings but seldom
see in real projects. That's a shame. It's a good joint and it isn't
difficult to cut on the router table. The joint's benefits are its clean
appearance, its improved stress resistance over a plain miter and its
ease of assembly.
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The dovetail rabbet joint is simple to make on the router table. You use
a dovetail bit instead of a rabbet or straight bit. The joint comes
together neat and square. It's more resistant to racking than a
conventional rabbet joint.
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Overall, rabbet joinery is simple to cut. Effective tools and techniques abound. The router, in my opinion, is the best all-around rabbeting tool. You can take the tool to the work, or the work to the tool. You can cut a precise width without measuring. You can rabbet curved edges, you can rabbet narrow edges.
It almost seems that rabbeting is something a router does best. Yes, it does do it well, but there are pitfalls to be wary of. It's awfully easy to gouge the cut or round the end of the shoulder when using the router handheld. And chipping at the edges of a long-grain cut is common.
There's more to the operation than merely selecting the rabbet bit with the correct cutting width, chucking it in your router, setting the depth of cut, and routing. But that's the obvious way to do the cut, so let's look at that approach first.
Rabbeting with a Piloted Bit
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| Routing a rabbet is usually straightforward. Use a piloted rabbet bit, guiding it along a smooth, straight edge. |
The first choice for the average rabbeting operation is the rabbet bit, which has a pilot. It minimizes setup: The only adjustments you can make are the depth of cut and the angle of attack. The measurement between the bit's cutting edge and its pilot governs what I call the width of the rabbet. (A lot of bit manufacturers call this the depth of the rabbet.) You insert the bit, adjust the depth setting, and rout. It is simple.
To alter the width of the rabbet with such bits, you can do two things. One is that you can change your angle of attack, as shown in the drawing. This can be a useful approach, since it can change the dimension over which you have control, while preserving the simplicity of setup and operation that pilot bits provide.
The other thing you can do is to change the pilot bearing. Every bit manufacturer sells separate bearings, and in the case of rabbet bits, they package sets that will give you many different cut widths from one bit.
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Interchangeable bearings make the rabbet bit versatile. A number of
manufacturers offer bearing sets to complement their rabbet bits.
Depending on the bearing used, a standard 1/2" rabbet bit will also give
you 1/8", 3/16", 1/4", 5/16", 3/8", and 7/16" cuts. That's seven
different cut widths from one bit. You can find packages with fewer
bearings, and with more bearings.
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(There is a third thing you can do, and that is to circumvent the pilot somehow — using an edge guide or a fence. You can only narrow the cut using this approach, but it's valid: it works. If you take this approach, though, you probably should question why you are using a rabbet bit and not a straight bit.)
The piloted bit can be used in both handheld and table-mounted routers, of course. Because the bit is piloted, you don't have to use the router table fence. (You should use a starting pin if you don't use the fence.) If you do use the fence, set it so it lines up with the pilot. Hold a straightedge so it bridges the bit gap in your fence, and adjust the fence until the pilot just touches the straightedge (without lifting either end off the fence).
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| While the rabbet bit has some limitations, it is easy to set up, cutting
predictable widths without time-consuming test cuts. And rabbeting
curved work is something only a piloted rabbet bit can do.
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Thwarting Splinters
The best way to avoid splintered edges when you rout rabbets is to make the first pass what I call a scoring cut. There are two ways to make it.
With a handheld router, make the first pass a climb cut. It's usually a wavering cut, because nothing is guiding it. Rather than hitting the wood fibers head-on and driving them out from the board's edge, the cutter is sweeping in on them, creating a crisp edge to the cut. On a second pass, feed the proper direction, cutting full depth.
There's good reason to be wary in making that climb cut. The router seemingly will try to run away from you. But the cut is shallow, so the cutter can't get much traction. And, of course, you have a firm grip on the router, too.
The approach on the router table is different. I don't like climb cuts on the router table, ever. So set the fence to allow the barest of cuts, only 1/32 inch, perhaps 1/16 inch. Feed in the correct right-to-left direction. The cutter glances across the wood fibers and doesn't get enough purchase to dig out an ugly splinter.
Reset the fence then, and cut the rabbet to whatever depth you desire.
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The best way to avoid splintered edges when you rout rabbets is to make
the first pass a very shallow scoring cut. While you might climb cut
this with a handheld router, such cuts are hazardous on the router
table. Instead, set the fence to allow the barest of cuts, only 1/32",
perhaps 1/16". The cutter glances across the wood fibers and doesn't get
enough purchase to dig out an ugly splinter. Reset the fence then, and
cut the rabbet to whatever depth you desire.
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Rabbeting with a Straight Bit
A straight bit is a very flexible rabbet-cutter. If there is a drawback, it is only that the setup can take a bit more time, especially with a handheld router. This is because you need a fence (or edge guide) to control the cut.
On the router table, you tighten the bit in the collet, then set the fence to expose only enough of the bit to make the desired rabbet. If your router table is like mine, then it's like the table saw — the fence is always in place, and adjusting its setting before making a cut is second nature.
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By using a fence instead of the pilot, you can greatly increase the
width of rabbet you can cut. Though only half of this 1 1/2"-diameter
mortising bit is engaged, the rabbet being formed is half again as wide
as one cut with a piloted bit.
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With a handheld router, you can either clamp a straightedge to the work, or you can break out the edge guide.
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Cut a rabbet of most any width with your router and a straight bit.
Clamp a fence across your workpiece to guide the router. Using a
T-square will ensure the cut is square to the edge of the workpiece. |
The advantage of these approaches is that you can produce an oddball rabbet, such as one to perfectly accommodate a piece of plywood.
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| Use a stock sample to set the bit exposure for a single rabbet. Hold the
scrap against the fence as you swing it into position and use your
fingers to ensure the bit's cutting edges are flush with the stock's
face.
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When rabbeting with a piloted bit, it's all too easy to inadvertently
"dip around the corner" at the end, thus botching the cut (left). Using
an edge guide helps you to slide straight out of the cut at the end,
thus maintaining the square corner. Keep a hand on the trailing end of
the guide to hold it against the work edge until the cutter is clear. |
Stopped Rabbets
A stopped rabbet, of course, is one that does not extend the full length of an edge. It can be stopped at one or both ends.
Here are two techniques for beginning and ending stopped rabbets, using a handheld router:
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In an ideal situation, the router woodworker can mark starting and
stopping points on the workpiece itself and track the bit's progress
visually. Setup is minimized.
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• Mark the beginning and ending points on the work. Make the cut between the two marks, visually aligning the bit with the starting mark to begin, and stopping the cut when the ending mark is reached. The accuracy of this approach depends upon the clarity of your vision and the steadiness of your hand. (It can be easier to do this if your marks reference the outer edge of the base, rather than the bit, since this relieves you of the need to sight through the baseplate's bit opening and the operation's chip storm.)
• Clamp stops to the work. The position of the stops would correspond to the marks that reference the base. You butt the router against the stop at the starting point and rout until it hits the stop at the end point. Clamping stops to the work can be said more easily than done in many cases.
Doing the same cuts on the router table can be a little easier. To visually align beginning and ending marks, make marks with a pencil on the router table fence that correspond to the edges of the bit (put a little masking tape on the fence if you don't want to mark directly on it). Obviously, your view of these marks won't be obscured.
To make the cut, you simply align the work beside the bit, push it against the fence (and thus onto the bit), make the cut, and pull the work away from the fence.
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| Cutting a blind rabbet on the router table is easy. Lay the work on the
table. Brace its right end against the fence, and keep the left end
clear of the bit. Align the start mark on the work with the mark on the
outfeed side of the bit. Push the work flat against the fence, beginning
the cut. Feed it to the left. When the end mark on the work aligns with
the mark on the infeed side of the bit, pull the end of the work away
from the fence. |
Almost easier still is to use stops. You can apply small hand screws to the router table fence as stops. The hard part is calculating the positions. The stop for the starting point will be to the right; the one for the ending point will be on the left.
• To set the starting block: Add the length of the cut to the measurement from the end of the cut to the end of the work. The sum is the distance the block must be from the left of the bit.
• To set the ending block: Add the length of cut to the measurement from the beginning of the work to the beginning of the cut. The sum is the distance the block must be from the right of the bit.
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| Regardless of how you rout a stopped rabbet, the cut's end will be
rounded (bottom). If the cut must be squared, you must find your chisel,
sharpen it, and square the cut's end by hand. |
Example: The workpiece is 22 inches long and the rabbet is 10 inches long. The rabbet starts 7 inches from one end, and ends 5 inches from the other. The starting block will be on the right, 15 inches from the left side of the bit. The end block will be on the left, 17 inches from the right side of the bit.
Obviously, the length of your fence can pretty easily be outstripped. When this happens, you can either attach a temporary facing that's long enough for the task at hand, or revert to the visual alignment of pencil marks.
Wide or Deep Rabbets
For purposes of this discussion, a wide rabbet is one that's more than 1/2" wide, for that's the maximum width possible using a piloted cutter. Here you need to use a straight bit. With a handheld router, use an edge guide or fence to control the cut. Obviously, on the router table, you'll use the fence.
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A scrap of stock stuck to the router's baseplate with carpet tape keeps
it from tipping. It's especially helpful when cutting a wide rabbet for a
half-lap joint. Here, the router's being guided along a fence clamped
to the work.
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Most router woodworkers have a 3/4" straight bit. Larger straights are available, though not that many of us have 2", 1 1/2", or even 1" bits. Do you have a large diameter mortising, planer, or bottom-cleaning bit? Any of these will do a great job. Use the largest diameter bit you have, however big it is, to produce those wide rabbets.
As the cut gets wider — wide to the point that you have to make three or four passes to complete it —avoiding wobbles and dips is the challenge. On the router table, you have to keep the uncut surface of the piece tight against the table. And if the ultimate cut is wider than the remaining uncut surface, then the last pass or two can be dicey. Pressure on the wrong area of the work can cause it to tip, gouging it. Doing the cut with a handheld router isn't likely to be any easier.
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| Forced to rout a wide rabbet with a relatively small bit? After the
initial pass, stick a shim to the tabletop with carpet tape. It'll
support the work and prevent you from inadvertently ruining the piece by
tipping it down on the bit.
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One solution is to treat the rabbet as a wide dado or groove. Cut the work with some excess width or length (whichever is appropriate), and leave a ridge of unrouted stock at the outer edge of the cut. This will support the router or the work. After the router cut is done, you trim the ridge of waste away on the table saw, reducing the work to its final width and simultaneously turning the dado into a rabbet.
An alternative is to use carpet tape to stick a shim to the router table
at the fence after making the first pass. The shim will support the
workpiece as you make subsequent passes.
Another approach is to deal with the rabbet as a deep cut. Address the depth of the rabbet with the fence or edge-guide setting, and address the width with the router's depth-of-cut setting. On the router table, you'll set the work on edge and feed it past the bit.
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Cut a deep (or wide) rabbet with a long straight bit by standing the
work on end (or on edge) against the fence. The cut width is limited
only by the bit's length. Featherboards will steady stock for a
long-grain cut, but only if they bear against it above the cut.
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Shiplap Joint
The shiplap is an underappreciated variant of the rabbet joint. Applications are somewhat limited, but where it works, it's a dandy. Use it for solid wood cabinet backs and chest bottoms, and for vertical-board siding.
Consider these advantages:
- It cuts quickly, since there's only one setup for both halves of the joint.
- No gaps open between boards, regardless of season. One board overlaps its neighbor.
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| A shiplap joint is formed by overlapping rabbets cut into opposite faces
of adjoining boards. The rabbets are quickly cut, precision is
irrelevant, yet they serve a valid purpose. |
Working out the joint dimensions is easy. One dimension of the cut is always equal to half the thickness dimension.
The second dimension is up to you. A good all-purpose width of overlap is 3/8". That's enough to prevent wood shrinkage from opening gaps between boards unless they are wide or the stock is wet. The wider the tongue formed by the rabbet, the more frail and subject to splitting it is. A 1/4"-wide cut yields a stronger tongue, but you may sacrifice the benefit of the overlap with a very narrow cut.
To adjust the cut depth, make a test cut, cut the sample in half, and fit the resulting pieces together. If one face is offset from the other, use a rule or the depth bar of a dial caliper to determine what it is. Your cut adjustment should be half that measurement.
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As a halving joint, the shiplap is easy (in concept) to fit. Cut a
rabbet on a sample of the working stock, crosscut it, and fit the joint
together. If the pieces aren't flush, measure the offset with a rule.
Raise or lower the bit by half the offset.
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Make a second test cut to assess the result of your adjustment. If further adjustment is warranted, make it.
With the setup established, cut the workpieces. Usually, you cut one edge, roll the board over, and rout the other edge. Typically, the boards are fastened with nails driven just shy of the shoulder of the "hidden" rabbet. The exposed rabbet catches under the adjacent board's hidden rabbet.
Embellishments: The shiplap can be embellished with bevels and coves and beads. These are intended to dress up the surfaces, creating interesting shadow lines and all that aesthetic stuff. But these embellishments also mask the seam between boards.
The caveat is to place these cuts where they won't degrade the joint. The obvious threat here is a bead that weakens the tongue.
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Chamfers and beads can be routed along the margins of the shiplap to
mask the seasonal change in the gap between boards. Chamfers can be cut
on both the rabbet's shoulder and the back edge of its tip so the
assembled joint has a V-groove appearance. The bead must be only on the
shoulder; it'll weaken the tongue.
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Mitered Rabbet
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For casework, the mitered rabbet is an improvement over the simple
miter. It looks like a miter, but each half of the joint has a shoulder
to make the joint easier to assemble and clamp.
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The mitered rabbet, as I said earlier, is a joint you see in drawings but seldom in real projects. A significant part of its disuse is that no one knows how to cut it. You can cut it on the table saw, but it's easier to do on the router table. You need a bit to cut rabbets and a bit to cut bevels.
Here's the sequence.
Cut a rabbet on one piece that is half the stock's thickness in depth and the full stock thickness in width.
Cut a rabbet on the mating piece that's half the stock thickness of both depth and width.
Make sure the rabbets are perfect before advancing to the next setup.
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The key to a properly fitting joint is to scale the rabbets accurately.
Begin by adjusting the bit height just as you would for cutting a
shiplap (bottom). For half of each joint, you cut a rabbet as wide as
the mating piece is thick (center). The other half of each joint
requires the width of the rabbet to match its depth (top).
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Switch to a chamfer bit and raise it above the table. The photos show a good routine for setting the chamfer bit and fence. But here's a slightly different way you might try: Use the "square" rabbet to set the fence position. Slide the end of the piece, rabbet up, under the bit body. You want the outer tip of the cutting edge against the shoulder of the rabbet and the fence against the end of the piece. When the fence is locked down, lower the bit until it contacts the bottom of the rabbet.
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The miters are routed with a chamfering bit. Adjust the bit height
against a rabbeted piece. The tip of the slanted cutting edge must align
with the bottom of the rabbet. |
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Set the fence after the bit height is set. Position a rabbeted piece
beside the bit, as shown, and adjust the fence to align the tip of the
cutting edge with the bottom of the rabbet.
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Cut a bevel across the tip of each rabbet.
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Both the wide and narrow rabbets are mitered with the same bit and fence
settings. Be sure to back up the workpiece to prevent splintering as
the bit exits the cut.
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