Woodworking Joints - Which Ones Should You Use?

There are many popular woodworking joints. A Woodworking joint's strength varies, and some are better than others.  Which ones are best for your projects?

1. Butt Joint

Biscuit

The Butt Joint joins two pieces of wood by merely butting them together. The butt joint is the simplest to make. It is the weakest joint, and you must use some type of reinforcement. You have an end grain to long grain gluing surface. The resulting joint is naturally weak. It relies on glue to hold it together; however, glue does not have much lateral strength. You can break this joint with your bare hands.

2. Biscuit Joint

A biscuit joint is nothing more than a reinforced Butt joint. The biscuit is an oval-shaped piece and is made of dried and compressed wood, such as beech. You install it in matching mortises in both pieces of the joint. Most people use a biscuit joiner to make the mortises. You design the biscuit joint to allow flexibility in glue-up. However, you must locate the mortise the correct distance from the face of the joint in both pieces. Since the biscuit is thin, you can move the alignment around. This is the very reason that I do NOT like this joint. It is not in perfect alignment. In addition, you waste your money on the Biscuit Joiner and a lot of time cutting the mortises in each piece of stock. Why bother?

3. Bridle Joint

 A bridle joint is similar to a mortise and tenon. You cut a tenon on the end of one piece and a full width mortise into the other piece to accept it. This is the distinguishing feature of this joint You have only three gluing surfaces.

The corner bridle joint joins two pieces at their ends, forming a corner. You use this joint to house a rail in uprights, such as legs. It provides good strength in compression and is fairly resistant to racking. You must use a mechanical fastener or pin.

4. Dado (joinery)

 A dado is a slot cut into the surface of a piece of wood. When viewed in cross-section, a dado has three sides. You cut a dado perpendicular to the grain. It is different from a groove, which you cut parallel to the grain. A through dado passes all the way through the surface and its ends are open. A stopped dado has one or both of the ends stop before meeting the edge of the surface. You use dadoes to attach shelves to a bookcase carcass. You rabbet the shelves to fit the dado, which makes the rabbet and dado joint.

5. Dovetail Joint 

The dovetail joint, or simply dovetail, is a strong woodworking joint, and is great for tensile strength (resistance from pulling apart). The dovetail joint is used to connect the sides of a drawer to the front. A series of pins cut to extend from the end of one board interlock with a series of tails cut into the end of another board. The pins and tails have a trapezoidal shape. Once glued, the joint is permanent, and requires no mechanical fasteners. Some people use a dovetailed dado, because of the tensile strength.

6. Finger joint

 A finger joint or box joint is used to join two pieces of wood at right angles to each other. It is similar to a dovetail joint except that the pins are square and not angled. The joint relies on glue to hold together. It does not have the mechanical strength of a dovetail.

7. Lap joint

 A half lap joint is made by removing material from each piece so that the resulting joint is the thickness of the thickest piece. Generally, the pieces are of the same thickness. You remove half the thickness of each. This joint is good for making workshop storage items.

8. Mortise and Tenon

One of the strongest woodworking joints is the mortise and tenon joint. This joint is simple and strong. Woodworkers have used it for many years. Normally you use it to join two pieces of wood at 90-degrees. A mortise is a cavity cut into a piece of wood to receive a tenon. A tenon is a projection on the end of a piece of wood to insert into a mortise. You insert one end of a piece into a hole in the other piece. A quality mortise and tenon joint gives perfect registration of the two pieces. This is important when building heirloom pieces.

9. Pocket-Hole Joinery

The Pocket-Hole Joint is nothing more than a Butt joint with Pocket Hole Screws. The pocket holes require two drilling operations. The first is to counterbore the pocket hole itself, which takes the screw head. The second step is to drill a pilot hole whose centerline is the same as the pocket hole. Most people use a pocket-hole jig, such as the Kreg Jig(TM). This jig allows you to drill pocket holes at the correct angle and to the correct depth. Glue should be used to strengthen the joint. Of course, the Kreg Jig(TM) costs from up to 0. To me, that is a lot of money when you can make the mortise & tenon jigs for a fraction of that price. Moreover, the mortise and tenon joint is much stronger.

10. Rabbet

 A rabbet is a recess cut into the edge of a piece of wood. When viewed in cross-section, a rabbet is two-sided and open to the end of the surface. An example of the use of a rabbet is in the back edge of a cabinet. The rabbet allows the back to fit flush with the sides. Another example is the insertion of a glass pane by using a rabbet around the edge of the frame.

11. Tongue and Groove

Tongue and groove is made by cutting a slot (groove) along one edge. The other piece has a tongue cut on the mating edge. As a result, two or more pieces fit together closely. You can use it to make wide tabletops out of solid wood. Some other uses are in wood flooring, parquetry, paneling, etc.

Woodworking Joints Torture Test - Wood Magazine Nov 2006

Are pocket screws stronger than dowels? Which of the woodworking joints give the most strength? Do screws add any strength to a joint?

For the "Wood Joint Torture Test" in WOOD Magazine issue #173, they created and then destroyed more than 100 joints.

Wood Magazine Shear test:

Mortise & Tenon Joint took 1,005 lbs/force, which is over two to three times the force to break compared to other joints.

Wood Magazine Pull Apart test

The breaking force for a Biscuit miter joint is 220 lbs/force; Dado 559 lbs/force and screws did not help.

For a Mortise & Tenon Joint, the wood failed but not the joint. It took 4,733 lbs/force nearly 2½ tons to pull apart.

Clearly, this test shows that the Mortise & Tenon joint is superior to other joints.

For more information on Woodworking Joints, including pictures and the video by WOOD Magazine showing the results of these tests, please visit http://www.provenwoodworking.com/woodworking-joints.html

Copyright 2009 - Jim McCleary of provenwoodworking.com. All Rights Reserved Worldwide. Reprint Rights: You may reprint this article as long as you leave all of the links active, do not edit the article in any way, and give author name credit.

Woodworking Joints - Which Ones Should You Use?

Jim is a woodworker with over 37 years of experience. He helps many woodworkers increase their skills with techniques, tips, plans, and jigs. Helping woodworkers is Jim's expertise. Visit his specialty site at http://www.provenwoodworking.com

Woodworking 101 - How to Properly Edge-Glue Boards Into Panels

There are several steps to consider in the process of edge-gluing lumber including (1) lumber selection, (2) cutting to rough length, (3) ripping, (4) jointing, (5) grain matching, (6) biscuit joining, (7) gluing, (8) clamping and (9) thickness sanding. Just how you go about these steps depends on the condition of the lumber, the capacity of your machinery and the final size of the glue-up.

LUMBER SELECTION:

Biscuit

If at all possible, try to have all boards in the glue-up out of the same tree. If that is not possible, select lumber that is of similar color and grain pattern. To my mind, the ideal glue-up looks like one, extremely wide board with the glue joints barely visible to the naked eye. Since this only an ideal, I always try to get as close to it as possible.

Another, less-important goal would be to have all boards in the glue-up of the same approximate width. I am not suggesting ripping the wider boards down to match the narrowest board as this would be a terrible waste of expensive lumber. I do suggest, however, ripping extremely wide boards in two to minimize the possibility of curling due to changes in humidity after delivery.

Straight or ribbon grain makes the best homogeneous final appearance while wavy or swirly grain makes for an interesting but more difficult glue-up. Swirly grain will require orientation of the individual boards to minimize the number of places that the grain line suddenly stops at the glue line rather than appearing to continue into another swirl in the adjacent board. This orientation is highly subjective.

CROSS-CUTTING TO ROUGH LENGTH

I always rough-cut my lumber into lengths an inch longer than the length of the final product. This allows the entire glue-up to be neatly trimmed to size after the glue is dry. It also makes the ripping and jointing process a lot easier as I will explain below. The same is true for the width of the glue up: Make sure it is about an inch wider than the final product after trimming.

RIPPING

Kiln or air-dried lumber often decides to bow into a curve as it dries and this must be corrected before a glue-up can be accomplished. If my finished glue-up is only 3 feet long and it is coming out of a 14-foot bowed board, it will be far easier and economical to get the curve out of the 3-foot pieces than it would to remove the curve from the entire 14-foot board before cross cutting. This is one reason that you should always do your rough cross-cutting before ripping and jointing. Another reason is that a 14-foot, 2" thick x 12" wide board is pretty difficult to control on a jointer or table saw.

If there is a bow in one or more of your rough-cut pieces, those pieces should first have the curved edges ripped off on the table saw. The concave side of the board should always be towards the fence. Measure from the fence out to the outside of the end of the board that is nearest the fence and set the fence to cut this width. Once you have trimmed off the convex side of the board, flip it over side-to-side and find the point where the outer edge of the board is closest to the fence (somewhere near the middle) and rip the board to that width. When all boards have been ripped straight, take them to the jointer.

JOINTING

The jointing process should now be fairly easy in that the boards have been ripped straight. Take shallow depth cuts to minimize the possibility of tear-out. In loose-grained lumber with a lot of swirls on the face side, tear-out is sometimes unavoidable. If this happens, try running the board over the jointer head in the opposite direction. If the tear-outs persist, you will have no other option than to rip the tear-outs away on the table saw. You will then have a sawn edge in your glue-up. If you have a clean-cutting table saw blade like a recently sharpened Forrest Woodworker II, this should not be much of a problem, especially if you plan on using a biscuit joiner to secure your glue-up. You probably won't be able to tell which glue lines are jointed and which are ripped in the final product.

GRAIN MATCHING

Lay out all the boards on your work bench and arrange them for best appearance. Obviously, if one side of the final product will show more than the other in a piece of furniture, then you will want to have the best-looking sides all on that side of the glue-up. Examples of this would be table tops and cabinet doors. You also must orient the boards so that the glue-lines are not accentuated, as discussed in the paragraph on lumber selection above.

BISCUIT JOINING

Whenever possible, make sure that you biscuit-join your glue-ups. I say, "Whenever possible" because you will not be able to use a biscuit joiner on very thin lumber. On the other hand, very thin lumber (3/8", for instance) does not usually have enough strength to pop open a joint. So, with very thin lumber, you will simply be using glue without biscuits. With regard to lumber ¾" or thicker, I have seen a number of table tops, cabinet doors and cabinet casings open up along a glue line after delivery. At this point, repairs are difficult or impossible so the extra step of biscuit joining is well worth the minor time and expense. Look on it as major headache insurance! If you don't yet own a biscuit joiner, there are a number of great machines out there including Porter Cable, Lamello and Freud. There are also two good alternatives to using a biscuit jointer: Those are the Festool Domino floating tenon joiner and the Freud Doweling Joiner. Different methods, same result.

When you have your boards laid out the way you want them in the glue-up, make sure all the ends are flush and the edge joints are touching. Double-check to make sure the glue-up will be about an inch wider than the final product after trimming. With a builder's square or a straightedge mark a pencil line in 4" in from each end of the rough glue-up across the grain, crossing all glue lines but not continuing over the side edges of the glue-up. Make a similar pencil line across the grain at the mid-point of the boards. Make additional pencil lines half-way between the other pencil lines until all pencil lines are about 6" apart.

Mark the boards on one end "A","B","C" or "1","2","3", etc. so that you can put them back together in the same order when it is time to glue them up. Put the boards aside and nail, screw or clamp a stop board (scrap) to the bench top, left to right in front of you and about a foot in from the edge of the bench. As you are applying pressure with the biscuit jointer, while making mortises for the biscuits, this stop board will keep the board you are mortising from moving away from you. Make a mortise wherever a pencil line touches a board edge on every board.

GLUE-UP AND CLAMPING

There are two ways to clamp up a glue-up: horizontally on the bench top and vertically with the first board mortised-edge-up in a woodworking vise on the end or side of the bench. In the case of horizontal glue up, place pipe or bar clamps about 2 feet apart on the bench top with the clamp handles hanging slightly over the edge of the bench. Pre-adjust the clamps to an inch larger opening than they will be when tightened. Place the first board on edge on top of and across the clamps with the mortises facing up. Do the same with all the boards, in order. Make sure you have sufficient biscuits for the job ready.

A small dispensing glue bottle with sufficient glue for the job should be within easy reach. The type of glue is important: If the glue dries too quickly you will have big problems and if the glue dries too slowly, you will be losing valuable production time. I like to use Franklin Titebond Glue indoors or Franklin Titebond II for outdoor applications. These are "aliphatic resin" type glues that can be easily cleaned up with water. Ether formula gives a very strong joint and has a reasonable, 45-minute clamping time. Both of these glues are widely available in hardware stores, home improvement centers and woodworking stores.

Run about a 1/8"-thick glue line down the center of the edge of the first board, making sure that the glue drops into every biscuit mortise along the way. Then apply short glue lines on both sides of every mortise. This should result in sufficient glue so that it appears squeezed out of both sides of every glue joint after clamping. Insert a biscuit into each mortise. With 2" lumber, you may need an extra glue line for the full length of the joint. There is no such thing as too much glue because you can wipe up the excess with a wet rag. There is, however such a thing as not enough glue and you will recognize that condition when you see that glue is not being squeezed out of the full length of both sides of the glue joint. That is called "starving the joint" and starved joints often open up later. Glue is cheap! Don't skimp on it!

Lay down the first board with the letter or number up and the mortised edge away from you. Apply glue in the same manner to each succeeding board wherever there are mortises and place biscuits in the far edge of each board, except, of course the last board.

The board ends should be flush and the left clamp should be about 6" in from the end. The right clamp should be about 1-foot six inches in from the right end. This is because you will be placing alternately spaced clamps on the top side of the glue-up so that there is a clamp (top or bottom) about every foot. The top, right clamp will be in about 6" from the right end.

Once you have all of this in place, start tightening the clamp handles. Clamp all the bottom clamps finger tight, then the top clamps finger tight. Then, go down the row of clamps tightening them fully, bottom, top, bottom, top, etc. With a wet rag, wipe off most of the excess glue. Turn over the entire glue-up and wipe the other side. Look at your watch or clock and add 45 minutes to the time. This will be the minimum clamping time, any time after which you may remove the glue-up from the clamps. Mark this time on the glue-up with a felt pen. If you have multiple glue-ups, you can stand this glue-up against a wall to get it out of the way while it dries.

If you have been paying attention to the above, then you can figure out how to do a vertical glue-up in a vise which is suitable for smaller glue-ups and is easier to manage. The difference is that when it comes time to apply the glue, you will clamp the first board at its center in the vise with the mortises facing up. Apply the glue and biscuits. Apply glue to the mating edge of the second board and place it in correct orientation on top of the first board, and so on. Place the first clamp 6" in from the end, in front, the second clamp a foot away from the first clamp, in back and so on.

Once your glue-up is out of the clamps, it is ready to be thickness sanded either in a drum sander or wide-belt sander. If you don't have either of these machines, don't worry. Most professional furniture-manufacturing shops in your area will be happy to thickness sand your glue-ups for an hourly rate. You might want to consider buying your own drum sander or wide-belt sander, if you can justify the expense.

It is best to know the maximum width capacity of the sanding machine you will be using: 48"-wide glue-ups will not pass through a 36"-wide sander. If you know that you will have this limitation in advance, simply make two, 24" glue-ups and glue those together with biscuits after the thickness sanding is complete. The glue line won't be perfectly even and so it will have to be sanded true with a random orbit sander. Your glue-up should be sanded to at least 150 grit. 220 grit is even better. Trim the glue-up on the table saw to its final dimensions, rout the edges, if appropriate, and then random orbit sand the final piece to 220 or 320 grit before finishing.

For some woodworkers, gluing up lumber may not be the most interesting part of the craft. It is one of the most important, however, because a glue-up done incorrectly can be a recipe for disaster. Furthermore, the way you orient the boards in the glue-up will have a lasting and irreversible effect of the beauty of the finished project.

Bob Gillespie

Woodworker

©2010 Robert M. Gillespie, Jr.

Woodworking 101 - How to Properly Edge-Glue Boards Into Panels

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