The story
When I started building a set of kitchen chairs, I chose mortise-and-tenon joinery because of its strength. I then pulled my red oak stock together from three outside sources, while also using leftover stock that I had on hand.
Making identical mortises was never a problem, because I use a setup with a plunge router and fence and follow a procedure I’ve seen in Woodcraft Magazine. Assuming all the wood I used measured the same thickness, I cut my mortises and tenons with the aim of centering the tenons in the workpieces. To do this, I installed a dado set in my tablesaw, raised it to the desired height, and cut the tenons, flipping the workpieces to saw both faces equally.
When the time came for assembly, I discovered that only a few joints fit perfectly. Many tenons were either so thick that they wouldn’t go into the mortises, or so thin that they rattled. My dial calipers confirmed consistent mortises, but the tenon thicknesses were all over the place, varying by as much as 1⁄16". At this point I found myself dumbfounded and more than a little upset.
Case analysis
Neal Halifax of Clemente, California, needed to look beyond his tablesaw setup to root out the problem. It’s likely that his misstep happened when he skipped prepping his stock to achieve the exact same thickness throughout the stack. He assumed that stock sold as a certain thickness was, indeed, that thickness, regardless of the supplier. Unfortunately, stock bought from different suppliers can vary by as much as 1⁄8" in thickness. Even then, purchased stock can vary in thickness from one edge of a board to the other. So even if his saw settings proved to be dead-on accurate, his attempt at making stellar joints was doomed from the start, accounting for his collection of hit-and-miss tenons.
Shop-smart strategies
Had Neal followed these pointers, his joints would fit snugly and prove rock-solid.
- Follow the established stock milling sequence in preparation for building a project. Flatten one face at the jointer, then plane to the desired thickness.
- Whether making one joint or several, use test pieces to confirm your settings. Tweak the settings if needed. If making several identical joints, occasionally test-fit the parts to ensure that your setup remains accurate.
- It’s a good practice to cut tenons fat, and then trim the excess with a shoulder plane or sanding block.
- If using a tablesaw to make tenons, press the stock flat to the table when running it over the cutter.
- To maintain blade height, make sure the adjustment crank is locked down.
- Periodically blow away dust buildup that can compromise the precision of jigs.
