How to Make Woodworking Joinery Half Lap Joints
Woodcraft Techniques for Strong and Tight Fitting Furniture Making
Mar 24, 2009
There are hundreds of carpentry joinery techniques. Many of these are specialized for particular applications. At one of the most admirable extremes is Japanese joinery. The shrine carpenters (miya daiku) are known for the intricate puzzle-like joints they produce.
This article will focus on a topic more utilitarian; how to make half lap joints.
Tools Used to Cut Half Lap Joints
This joint lends itself to working with lumber stock of the same thickness. Basically, the same amount of wood is cut away on each piece (half of it). This way they can be mated together and the finished project retains the thickness of each piece alone. Very simple, very unpretentious.
This construction dictates the kind of tools that work best.
- Use a router table – A router table is ideal for smaller projects, such as models or wooden toys.
- By hand with a coping saw – Coping saws have very thin blades. This allows for working on small wood crafting projects.
- A table saw with a stacked dado set – This method works great for larger jobs (stock 2” to 4” thick or so), like repairing table or chair legs.
- Using a band saw – When the size of the stock gets thicker than a 10” table saw blade will handle, look no further than the upright wood shop band saw.
Table Saw Set-Up
As with other stationary power tool operations, proper and accurate set-up usually takes the most time. Do it once and make all the cuts that are practical.
The first thing to do is determine the width of the cut. Then set up the dado set stack and mount it securely on the saw's arbor. It's important to set the blade cutting depth exactly right. Use a scrap piece of stock that's the same size as the project material to test it.
Once you've got the proper depth set, go ahead and make all the cuts needed. For the sake of safety and to eliminate or minimize side cut out, use a zero-clearance dado insert. These are great homemade woodworking jigs to make and keep in the home shop.
Finally, Assemble the Stock
Just like when assembling dovetail joints, it's important to dry-fit the project and do any fine-tuning needed. Next, spread the glue on both pieces and clamp them up. Titebond III glue is a good choice for this joint.
Since some squeeze-out is almost inevitable, it's advisable to set the joint up to dry on a sheet of wax paper.
Giving a Half Lap Joint a Dose of Strength
One great thing about the half lap is that it affords a huge about of open-grain glue contact. This is the secret to any joinery technique. But on any project that will sustain lateral stress, it's best to err on the side of caution.
For this particular style of woodworking, here's a great tip. After the glue has set up, drill straight through the joint in two or more spots and glue in hardwood dowels tightly. This will as much as double the strength of the combined stock and gives it a bit of artistic flair when dowels of a color contrasting with the stock are used.
