Calipers are useful tools for quickly checking the diameter or width of something. They’re useful when dealing with parts that don’t have regular measurements. Whatever the size of the part, the caliper will help you transfer that measurement. Using calipers makes it easy to make identical copies of parts or make two pieces of wood fit snugly together. Calipers come in many different varieties, designed to deal with the type of material they were made to measure. This article teaches you about the different kinds of calipers used in timber framing and how to use them.
There are really only 2 types of calipers; outside calipers and inside calipers. Outside calipers are used to measure the outside width of an object; the distance the caliper tips can pinch the object before stopping. Inside calipers are used to measure the internal width of an object; the distance the caliper tips can spread before being stopped. You can get away without having this tool for timber framing. It’s not a “must have” by any means. But it makes joining timbers easier and faster, and I would argue one can make tighter joints with calipers. I suggest adding them to your tool box when you come across a good vintage pair (L.S. Starrett of Athol, MA is my personal favorite for calipers and other measuring tools. The quality of their tools is top notch.) If you’re buying vintage, make sure the caliper tips meet squarely and the hinge is tight, tight enough to lock in place. Some calipers come with a screw mechanism to lock them in place, which I find helpful in some situations.
Inside calipers are useful when checking mortises for high spots. Even as little of 1/16″ can cause problems when it comes time to fit the tenon into the mortise. Slide the inside calipers along along the inside of the mortise. If the calipers get stuck on a high spot, pare it down with a slick or chisel.
Inside calipers are also useful when fitting replacement handles on tools. For example, use the them to measure the eye of the axe, then transfer this measurement to the new replacement handle.
Outside calipers are used in timber framing to check tenons for the proper thickness. Run the calipers along the two cheeks, if it sticks on a high spot, pare it down. It’s a lot easier to find high spots with calipers than it is to test fit two large awkward timbers.
You can also use calipers to scribe your work. In the picture to the left I’m using my outside calipers to fit a handle to a wood mallet. I’m pressing the calipers into the wood as I move it down the length of the handle to scribe a line. I’ll darken the line with a pencil and remove the waste wood with confidence.
You’ll want to have a set of both kinds of calipers. I use mine all the time when trying to make two parts fit together perfectly, like mortise and tenons and fitting replacement handles on my tools. Once you understand how to use calipers they become indispensable around the workshop. Instead of constantly test fitting your work, the calipers tell you when the desired thickness has been reached. Calipers take the guess work out of joining timbers, allowing you to work faster and make tighter joints.