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Making Joints Between Project Components

Introduction

This page describes the various joints that I use to make a project from its individual components. For example, I often join the sides of a box together with a miter joint because this results in no end grain being visible. On this page, I also describe or include links to methods of making these joints in a full-equipped workshop and then describe how I make them with my limited equipment.

Butt Corner Joints

I have not yet made anything with butt corner joints that I would call "woodworking".

Rabbet Corner Joints

I have used rabbet corner joints in a puzzle project.

Miter Corner Joints

Miter joints have the great advantage that they expose only face grain on the outside of the workpiece. The wood can appear to turn the corner almost by magic, as if simply folded. However, without some kind of reinforcement the miter is known to be a weak joint. I haven't found what I'd consider an authoritative explanation of this. A miter joint is made between two end-grain surfaces. Woodworkers and glue manufacturers agree that glue does not work as well on end-grain as on side-grain. This apparently has something to do with the glue soaking into the end-grain and Titebond publish a tip suggesting that the end-grain be "sized" before final application of the glue and assembly. Even so, forces that are likely to snap the joint appear as tension (pulling apart) that is strongest at one edge. The opposite edge acts as a lever to magnify the applied force. It is easy to see how a break can start at the most stressed edge and propagate across the whole joint. Miter joints can be reinforced in various ways by adding structures that expose side-grain to the glue and take breaking forces in shear (side-to-side) mode. I have not yet made anything that uses a simple, un-reinforced miter joint, but see the following sections for types of reinforced miter joints that I have used.

Miter Joints with an External Spline

The slab-lid keepsake boxes that I have made use mitered corners reinforced with splines that run across the joint and are fully exposed to view. The splines are fixed to the box sides with face-grain glue joints, which are reputedly stronger than the actual wood itself. Stress applied to the corner appears as shear forces at these joints, which is much less likely to result in failure than tension. The use of splines in this way completely solves the problem of miter joints being weak. It creates the problem that you now have these very visible extra pieces of material interrupting the flow of the wood grain around the corner. It is possible to minimize the visual intrusion, but I have gone in the other direction and used contrasting wood species to make the spline a design feature.

Miter Joints with an Internal Spline

If you have a good quality table saw, you can add an internal spline to a miter joint with just the miter gauge and auxiliary fence that you used to cut the miter in the first place. For an excellent explanation of this process, take a look at this video by Inspire Woodcraft. The video includes background information about why you would use this joint and the direction of the wood grain in the splines for maximum strength.

My table saw is of poor quality and I don't believe I would get good results cutting miters of any sort directly on the table (it is significantly out of flat). Instead, my approach is to leave the blade angle at zero (vertical) and use a jig that holds the workpiece at exactly 45°. This jig rides inside my crosscut sled and does not rely on the flatness of the table.

Go to the Wiki section about my first small box with internal splined miter corners.

Miter Joints with Dowel Reinforcement

The idea for reinforcing a miter joint with dowel pins popped into my head as I was preparing to make a substantial number of keepsake boxes with internal spline miter joints. I was having cold feet about the splines as my plan was to modify the box design. The lid would no longer conceal the end of the spline on the top edge of the box. My first thought was to route a slot for the spline that stopped short of the top and bottom of the joint, but I was concerned about stress on the very thin router bit that I would have to use. Then I thought of the 1/8" and 3/16" dowels that I had recently bought to make the hour / 5-minute dots on clock faces and I decided to try using pins made from that. I'm sure other people thought of this first, I just haven't come across the idea or I've forgotten about it.

For a miter joint in a small box with, say, ½" thick sides, a few 1/8" dowel pins will not provide the strength of either a top-to-bottom internal spline or a similar number of external splines (I have bought a 3/16" straight router bit and use thicker dowels next time). But, making the pins is going to be much easier than making the splines, the pins will be completely hidden inside the joint and they will make the glue-up easier by positively locating the pieces being joined in all directions. I do, however, have to figure out how to drill the holes in the faces of the miter joints in exactly the same place on the mating pieces. The following is a terse description, mainly for my own records, of how I managed this for the particular project I was working on.

• Fit the 1/8" straight router bit to my router mounted in the table. (This is a single-flute, solid carbide bit. Maybe I should have paid the extra for a two-flute spiral bit.)
• Adjust the router depth stop so that when I lift the router the tip of the bit rises ¼" above the table plus a tiny bit more. With ¼" deep holes in each piece, the pins will need to be ½" long. A little extra depth in the hole will accommodate error in cutting the pins and some glue trapped in the bottom.
• Move the fence from my table saw to the router table and set it at the 68 1/16" mark. Place my miter jig up against the fence so that the workpiece, when mounted on the jig, will have its mitered face over the router bit. The setting of the fence puts the holes that will be bored at a suitable depth into the joint.
• Carefully rip the workpieces as close as possible to a width if 2" (I achieved about 2.002"). At the same time, make a test piece to be used for setup. Mount it in the jig.
• Align the axis of the router bit with bottom edge of the test piece. Clamp a stop block on the fence against the end of the jig to locate it in this position.
• Slide the jig forward and put a (precise) half-inch spacer between it and the stop block. Pull the jig back against the spacer and hold it tightly in this position. Move the stop block to this new location.
• Make sure everything is held tightly in place and lift the router (using the lever built into the router table) to bore the first hole.
• Slide the miter jig forward and insert a (precise) 1" spacer block between it and the stop block.
• Hold tight, lift the router and bore the second hole.
• Remove the 1" spacer.
• Remove the workpiece and either flip it around, move on to the next one or finish.
• If not finished, go back to the step in which the workpiece is clamped into position.

On the first try, I got this almost spot on. On my second try, I was misaligned by 0.016".

Box Corner Joints

I have not yet made anything with box corner joints. I don't find them particularly attractive.

Dovetail Corner Joints

I have not yet made anything with dovetail joints (since high school, anyway).

Dado Joints

Dado joints are great for installing fixed shelves in some kind of cabinet, but I've not done anything like that that I would call "woodworking" as opposed to just carpentry.

Through Tenon Joints

I used through tenon joints on the Toothbrush Holder.

Here's an interesting video on "simple" wood corner joints. In addition to what I've covered above, he shows exposed dowel-reinforced splines, angled splines, dovetail splines and dovetails with mitered corners.