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I cannot imagine the number of mortise-and-tenon joints I’ve cut throughout the years. One of the pieces of furniture I’ve built numerous times, a Shaker Sewing Desk, has 55 of these joints. So, over the years I’ve developed an efficient process to cut a mortise.
No hand tools for me. I don’t have the time or the desire to do this work with a chisel and mallet. For me, it’s not the process of building the furniture, it’s the completed piece of furniture I strive for. I use a dedicated mortise machine.
I began woodworking with a bench-top mortiser. In fact, I wore out two machines before purchasing a Powermatic 719A, the old model without a tilting head. The 719A is available as a Jet JFM-5, although it’s white and not gold (click here to read a blog entry about this machine).
With any mortise machine, the steps I take to a completed mortise are the same. The first step is layout and tool setup. The method I use most often is to find the center of my stock, then I align the point of the bit to that line. I turn the machine on as I dial-in this adjustment. The points on these bits are sometimes slightly off center. When the machine is running, the turning point becomes apparent.
After setup, make a series of plunges to cut your slot. Then make sure to reverse the stock and make a second run at the mortise. That guarantees the mortise is centered; even with accurate setup, it’s possible to be off a minuscule amount and that can have an impact on your work. If you’ve ever had doors that gently twist from top to bottom, not centering your mortise may be the cause.
I use a different setup for wider mortises. For these I position the chisel a measured amount off the machine’s fence. Make a series of cuts to form one side of the mortise, then reverse the stock and make a second series to create the slot. Again, I know the mortise is centered and equally spaced from the edges of my workpiece. Any additional waste remaining at the center is removed in another pass.
While setup is important, what I find most interesting are the results from the actual cutting of the mortises. The photo at the top of the page is a completed mortise. It differs from the photo directly above due to an extra step in the mortising process.
If you cut the mortise in a single pass, the slot is created, but the amount of waste remaining in the mortise is substantial. To complete the mortise and leave it clean and nearly waste-free, take a second run in the slot. However, on this pass forget trying to remove as much waste as possible with each plunge and take baby steps. The extra pass is quick and the result is a cleaner, ready-to-go mortise.
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