Wood School: Cutting Tenons The mortice and tenon joint is one of the simplest and yet most effective of all woodworking joints. In cutting the tenon part you will have covered some of the key woodworking skills: marking out, handling a saw, cutting with the grain, cutting across the grain and paring with a chisel. Simple%20sawing.htmlshapeimage_2_link_0
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Simple tenons There are many different types of tenon, each used for different situations. One of the best books on the subject is The Joint Book by Terrie Noll, which shows many of the options and how to cut them. We are going to show how you cut a very simple tenon, and then how it progresses to become something more complicated. 1 Starting out You start by marking out the tenon using a mortice gauge. This produces parallel grooves to guide your tenon saw. You set the width between the pins on the mortice gauge to match whatever chisel or cutter you are using to chop out the mortice. The mortices should be cut first and the tenons made to fit because the width of the mortice is determined by the cutter whereas you can alter the tenon to whatever size you want. The terminology is confusing, but the width of the mortice should be about 1/3 of the thickness of your timber. 2 Terminology Because the mortice is effectively a hole, and the tenon a piece of wood, the terms used to describe their dimensions differ. Width of mortice = Thickness of tenon. Depth of mortice = Length of tenon. Length of mortice = Width of tenon. Don’t expect this to be consistent between all books and magazines and woodworkers! Tenons are usually found on rails, which are usually horizontal, and mortices on stiles, which are usually vertical. 3 More marking With your mortice gauge set you can mark up the tenon, but first run a line using a carpenter’s square around the board to show the shoulder line. Often you will cut the tenon too long in case the end gets damaged, and it is the distance from one shoulder to another on the same rail that is critical. Make sure the shoulder lines around the board meet at the end. If they do not either your square is inaccurate or the board isn’t properly planed. 4 Cutting by hand Often the quickest way to cut a tenon is by hand. Machines take longer to set up to cut the joint accurately. You will quickly work out which tools might substitute for the simple tenon saw. The aim is to cut your tenons accurately so there’s no paring with a chisel needed afterwards. 5 Cutting the cheeks You start by cutting down the tenon cheek. Angle the tenon away from you so that you start at one corner and cut down at and angle to the rail. Once you reach the shoulder line nearest you, turn the rail around in the vice and do the same from the other side. Always cut to the waste side of the line. Then, with two angled cuts, you can position the tenon upright in the vice and cut down vertically till you reach the shoulder. 6 Cutting the shoulders Having cut the cheeks with the rail in a vice you can cut the shoulders. This is best done just with a bench hook as a holding device. You shouldn’t need to hold the rail with anything other than your hand. Line up the saw on the waste side of the line and cut down a shoulder until the waste drops away. Cutting the shoulder is an excellent test of sawing skills: any discrepancy will be seen in the assembled joint. The important thing is to keep the saw vertical so it cuts the shoulder square to the face. 7 Cleaning up A little mound of waste is often left in the corner between the shoulder and the cheek. This needs to be removed or the tenon won’t close tightly. Don’t touch the shoulder with a chisel as you are likely to ruin the straight line you have just cut. Instead, hold the chisel upright, with your hand around the top of the steel, the handle facing away from you. Then use the corner of the chisel edge to scribe into that waste. Once that is done you can pare the waste away with the chisel on the cheek, working gently across the grain. If your tenon saw wandered at all, and it will do to start with, you can clean up the cheeks using the groove from the mortice gauge as a reference. You will often find that it is easiest to work across the grain. Check the tenon for fit in the mortice, or in a trial mortice if you have chosen to cut your mortices afterwards. It can help to chamfer the leading edges of the tenon to ease it into the mortice. 8 Checking the fit How tight the tenon needs to be depends on the type of wood you are using. For softwood you need to be able to knock the tenon home firmly with a rubber mallet otherwise it will be too loose. For hardwood it just needs to slide in smoothly with hand pressure or a gentle knock. If it’s too tight the hardwood might split. Choosing a tenon Once you can do that you can cut any tenon. It then becomes a matter of choosing the right one for the right job. Often it comes down to balancing the strength of the tenon and the strength of the mortice. If the tenon is very long and very wide you will need a large mortice, which will weaken the mortice piece (stile, usually). One of the key aims is to stop the tenon twisting in the mortice. So at times you may choose to have the tenon to the full width of the board, but shorten the tenon at one or both ends to reduce the size of the mortice. This is called haunching. The haunch stops the tenon twisting without weakening the mortice piece. Tenons can protrude all the way through a stile, in which case they are known as through tenons, or stop short, in which case they are called stub tenons. With through tenons you get to see the end of the tenon, and can insert wedges if you like to tighten the joint, but it does mean the mortice is large and you have to cut accurately to get a tidy fit. Terrie Noll’s book shows many options. The UK’s No.1 Woodworking Magazine
 
Cutting Tenons: Details Drawings and photos to help you cut tenons better Fig.1 The full width tenon. Though you can have a tenon with just one shoulder, the most common one has two shoulders, like the one above. The thickness of the tenon (T) is 1/3rd of the thickness of the board. The width (W) of the tenon is the same as the width of the board, and the length (L) of the tenon suits the depth of the mortice. The tenon thickness is traditionally divided into threes to equalise the strength of the tenon and the area of the shoulders to support the tenon. You mark up the tenon with, confusingly, a mortice gauge!