What Causes Wandering Tenon Cuts?
I recently cut a lot of tenons for a mission style bed using a dado setup (rather than a tenoning jig) on a JET saw with Freud dado set. I set the fence to the proper depth, and used a standoff to insure the work will not wedge between the fence and blade. I checked the miter to blade angle (90 degrees) using an L square. In spite of my best effort, I noticed that some (not all) of the cheek cuts "wander". The shoulder cuts do not line up, or the cheek cuts are cut at an angle. The end result is a tenon that does not seat perfectly in the mortise. Even though I concentrated on holding the work tight against the miter, could the blade be pulling the work through the cut?
Michael Dresdner: It certainly could, especially if you are holding it by hand, though what is far more likely is that it is being pushed away. The result is the same - a non-square cut. Next time, cut the tenon shoulders first with a single blade. You'll find that a blade captured in wood will not pull or push as much as one cutting with one end free.
Rob Johnstone: A couple ideas occur to me. First, the stock that you are machining is not perfectly square. (Face to edge, edge to face, end to face and edge; you get the picture.) If the faces and edges of the stock that you are cutting are just a few degrees out of wack (a technical woodworking term), the lines defining your tenons will be off by that amount. The visual result is exacerbated (a fancy-pants editing term) by the fact that every cut will be held against the same orientation fence (your miter gauge) and therefore you need to rotate the stock as you go. Hence, the deviation of the cuts on opposite sides of the board will be running at odds to one another. (It will show up more.) The second thought would be that perhaps your dado set has run into hard times (like a screw or nail hidden in some wood) and is cutting better on one side of the set up than the other. I own a Freud dado set and have nothing but praise for it. I work it hard and get clean accurate cuts all the time. I do have it sharpened every now and again.