How do you pick a joint?

Question

For a novice working on a design, picking a joint seems a very daunting task. There are many different kinds and it isn't easy to pick the most appropriate one. How to position the different elements, and where the main stress vectors lie is somewhat intuitive, but joints appear to have developed significantly over the centuries and there are many non-obvious innovations that a novice is unlikely to re-invent on his own. Moreover, the "obvious" solutions that would readily occur to a novice (like a butt joint with nails) are often regarded as inappropriate.

If you search for "best joints to use", often the results have a lot of joints that would require specialized tools one might not have access to. Worse, sometimes the best joint is the most complicated one, because it shows off the skill of the carpenter. Obviously not appropriate for someone seeking the path of least resistance.

Given a certain set of tools and known structural demands, how does one identify the best joint to use for a project? Is there some kind of flowchart or table?

Answer 1

When I was beginning to do woodwork projects I often selected the joint I had not done before. To me it has always been about learning something new.

Most joints are strong enough for most common applications, the exception being connections that will have higher stress and changes in direction. Chairs are an excellent example where heavy loads must be transferred between horizontal and vertical directions. Not only that, they must absorb high lateral loads as people sit or stand or even drag a loaded chair across a floor. All these loads are transferred from the seat or arms to the legs. The wood, if properly sized can carry the loads along the length of the board, but the corners must translate the loads in a new direction. This is commonly accomplished by two features in the joints. First, the creation of recessed connections such as dadoes or mortise and tenon joints use the strength of the wood to restrict the angles of movement of the joint. Second glue contact surface transfers the loads between the pieces at the joint. The more glued contact area between parts at the joint, the more load the joint will be able to handle. Consider a drawer in a dresser as an example. A good dresser could easily be used for 50 or more years with multiple openings daily. A simple dado joint might eventually fall victim to any flaws in the connection. The joint of choice in this case is a dovetail which uses the strength of the wood to hold the drawer corners together and a very large glued contact surface to transfer the loads throughout the drawer assembly.

So how do you determine which joint is appropriate for any project? The simplest means for deciding is to look at what experienced woodworkers have done before. Wood joinery traditions go back millenia and the experience and skills of these craftspeople are all around us. In each new joint challenge ask yourself what forces will be experienced, what directions the force will come from, how long the finished project must last, how much time do you have to complete the project, and whenever time permits, how much will I learn and how much fun will I have making this joint.

Answer 2

Most woodworking books will adopt a ground-up approach, teaching a range of traditional joinery techniques to begin with, may illustrate examples of where such joints are used in everyday projects and/or give projects that use some or all of them.

Joints are generally presented from simplest to most complex, so for example a modern book that's a little simpler will usually have butt joints first, then maybe overlap joints (half-laps), housed joints (rabbets and dados), then mortise-and-tenon joints, with dovetails often left to last. In addition to going up in strength these joints increase in difficulty and complexity so they make a good training progression.

If you search for "best joints to use", often the results have a lot of joints that would require specialized tools one might not have access to.

Few joints actually require specialist tools, although it depends on what you define as specialist. As should not be too surprising all traditional joints in both Western and Eastern woodworking can be accomplished using just a core set of hand tools — basic layout tools (rule, gauge, pencil, marking knife etc.), one or two saws, a couple of chisels and a hammer or mallet. That's literally it in terms of what's absolutely required, and all the joints listed above (and many more) can be done using only these if necessary.

Obviously for producing some joints additional tools are very helpful, e.g. a rebate plane for rebating/rabbeting work, a router for housing joints/dadoes. These additional tools may be thought of as specialist when starting out but they are considered fundamental tools for a fully equipped workshop and would be on a "next tools to get" list after the basics are covered.

Given a certain set of tools and known structural demands, how does one identify the best joint to use for a project? Is there some kind of flowchart or table?

There may be such a thing but I don't think you need to hunt for one.

A good starting point here is the realisation that much joinery is an exercise in over-engineering, which is to say that furniture joints are regularly far stronger than truly needed given that most furniture just sits static almost all of the time. And when it comes to withstanding movement joints are still often stronger than absolutely required. So based on this you can often choose the least strong option and still end up with a perfectly reasonable result, depending on the requirements obviously.

Now you can come at this from a completely different direction — if you always pick the strongest suitable joint you'll never need to worry about strength :-)

Most amateur woodworkers building for themselves aren't particularly worried about making stuff that will last and last, and TBH I think this is appropriate. If one or more joints in a project were to fail say 10 years down the line that's not necessarily the end of the world since you might be ready to get rid of the thing at that point anyway. That's not to say some simpler joints can only last that long but until you start to make stuff with the deliberate intention of it enduring ("heirloom pieces") you probably don't need to worry about what is the best joint for a given location*.

Some joinery is not just about strength
Some joints are intended to be seen, and have been and continue to be a means for the workman to show off their skill. The most obvious example I'm sure is through dovetails, which even if simple in form can still show great skill if done with precision resulting in a super-clean result.

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*Once you do get to this point you should be knowledgeable enough (through education and experience) to be able to unthinkingly pick a suitable joint, or you'll be building from a plan where each joint is specified and you just stick to the plan.

Answer 3

The joint you pick at any time should always have an answer to simple questions like; Will it hold the wieght? Will the structure be firm? How does it interlock with other joints? When building sensitive pieces like a wheelchair ramp ensure you pick just the right one as this can be detrimental.