The adz is bevel-up edge tool with a blade perpendicular to the wood handle. There are many different shapes, sizes, and weights depending on what the adz was designed to do. There are “foot adzes” that have long handles and are swung so they end up under your shoe (hence foot adz) and there are “hand adzes” which have short handles that are swung with just one hand. The adz also comes in different shapes, from the straight-ish carpenters adz used to flatten boards to the curved adz (gutter adz, bowl adz) used to cut grooves and hollows.
The shape of the adz varies depending on it’s intended use. For timber framing, we need to make the timbers flat and smooth, so we’ll use regular carpenters foot adz like the one in the picture at the top of this article. A lipped ship builders adz will work too.
The handle of the adz is either straight or curved, depending on your preference. One thing just about all adz’s have in common is that they’re hard to sharpen with the handle on. Therefor, most adz’s have a tapered handle to fit the tapered eye of the adz. The head of the adz can be slid up and off the handle for sharpening. Gravity and the inertia of the swinging motion keep the adz tightly mated to the handle when in use.
To use an adz, stand on top of or directly over your work. Hold the adz with your dominant hand lower on the handle and your other hand fixed against your body to act as a pivot point. Lift the adz up with your lower hand and swing it downward so that it shaving a chip off the board. With some practice you should have the confidence to bring the adz down right under the toes of your boot, keeping the wood chip from tearing out wood fibers ahead of the blade. If you’re not comfortable standing on top of the work and ending the adz stroke beneath the sole of your shoe, you can try standing to the side of your work… but I don’t recommend it. I’ve found this be more dangerous. Here’s why: If you’re standing to the side of your work and the adz glances, jumps, or ricochets off the board it could end up in your shin. Ouch. If you’re standing directly on top of your work and you have a glancing blow, it’ll miss your leg as it goes harmlessly by. It may help to work at an angle to the grain of the wood. Working at an angle or across the grain will reduce tear-out of the wood fiber.
The steel in an adz is hardened to the same hardness as a chisel. To sharpen the adz, remove it from the handle and use oil stones, water stones, or sandpaper. Don’t use a file, it won’t work. A file will just skate over the adz, it’s too hard to dig in and remove metal filings. I like to use a sanding block made from marble tile. You can attach sandpaper to a block of wood but use seasoned hard wood and be careful if it starts to form a divot as the wood compresses. If you attach your sandpaper with 3M adhesive it will be difficult for you to remove the adhesive when replacing the sandpaper. You want the sanding block to be dead flat. If your wood starts to indent, get a new piece of wood. A marble or glass sanding block is hard, flat, and won’t indent. Cleaning up adhesive with acetone and a razor makes replacing the sandpaper a snap.