If you’re looking to cut tenons using machines – a table saw in this case – there are generally two methods most often discussed. Those include the use of a dado stack and what I call a two-step method using a tenoning jig. How tenons come off the table saw using the two methods can be quite different.
With the two-step technique, the first cut, at least for me as I work this method, is to define the shoulders while the workpiece is flat to the saw’s table. (I use my miter gauge.)
The second step employs a tenon jig that stands the piece vertically as the cheek cuts are made. You can finish the tenons using the jig, but I often finish the edge cuts at a band saw or using a handsaw. This is my preferred method because my tenons come off the table saw with smooth faces, as shown in the opening photo.
Using a dado stack, for me, is a second choice. (For my 360 WoodWorking cohort, Chuck Bender, it is his preferred method – there is no accounting for taste…in tenon formation or cohort selection) Why this is relegated to second place for me has to do with the lack of smoothness in the resulting faces.
Of course, that characteristic has as much to do with the quality of your dado stack, as it has to do with the process. A good stack produces a smoother finish. Conversely, a less-expensive stack can often leave a stepped surface; it has to do with the relationship of the chippers to the dado stack blades.
If the chippers are slightly smaller in diameter to the blades, a ridge is left after the cut. And because you generally cannot make the entire cut in a single pass, you often have multiple ridges left when finished. Below are the two examples placed side-by-side.
Why would you ever use a dado stack to produce tenons? One reason is that this process is very quick; it’s often completed in a single setup. Another reason to work this way is that you are in need of fitting your tenons individually to the respective mortises – this could be due to the fact that you’re cutting your mortises then cleaning the sides, which changes the overall width of the slots. (Think drilling out the waste using a drill press, then paring the sides with your chisel.)
A third reason, and what I suspect is the reason most woodworkers employ this process, could be that your materials are at different thicknesses as you begin the mortise-and-tenon process – .001″ can make a difference in how tenons fit. I’ve found this associated with planer knives that are slightly out of level.
While these differences are off-the-machine differences, for the most part woodworkers do not use dado-stack-cut tenons right off the machines. In fact, most of the time these tenons are hit with a plane or rasp for the final fit. If that’s how you work, great. But don’t choose a technique without analyzing why you’re using it. There may be a better method of work.