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Zoiks, Like It’s the Case of the Phantom Tenon

10 years ago

Fitting a joint is a magical moment. It doesn’t matter whether it was cut with smashed electrons or burned calories, once you slide those pieces of wood together to form a seamless joint you cannot help but smile.

Unless of course that joint won’t close up and leaves a gap. It’s kind of like leaving the cadence off a piece of music or the punch line off a joke. It throws off the karmic balance of one’s woodshop and must be corrected before anything else is done. That sometimes includes sleeping, eating, and breathing!

So you can imagine my despair when after hand cutting a mortise and tenon, ensuring that everything was flat, square, and to size there was a 1/4″ gap at the shoulder. What’s worse, the tenon slid into the mortise with such smooth precision until it stopped firm.
This was not the slow stop that you get when the tenon is too thick and it binds. This was a thunk like the tenon was too long for the mortise. The crazy thing is the mortise is open at the top so I could look down the side and see that I had a 1/4″ gap at the bottom of the mortise. It seems as if the tenon was sporting a phantom extra 1/4″ and it was pining for it’s amputated tip.

My list of tips and tricks spun through my mind on how to close up a gappy shoulder and I checked off each one by checking the work.

1. The tenon shoulders were square and not interfering with the fit.
2. The mortise walls were flat and didn’t taper.
3. The floor of the mortise was flat and consistent depth along it’s entire length (I used the router plane to verify)

What the heck???? I even posted my dilemma on Twitter and received the expected responses from my virtual helpers. I kept going back to that “thunk” feeling when the tenon apparently bottomed out. It couldn’t be binding because it just wouldn’t stop in the joint like that. There had to be something physical stopping the joint from going together. Out came a flashlight and I began sighting into the end of the open mortise while the tenon was in the joint. Sure enough there was a sliver of wood that was popping out and preventing the tenon from closing. It was a sliver only about 1/8″ across that was anchored to the bottom of the mortise and as the tight fitting tenon pushed into the mortise, the splinter edged out only a tiny bit but acted as stop. Since the sliver was practically centered and the fit was so tight, it firmly stopped the joint from closing along the entire width.

What was amazing was once the tenon was removed the sliver practically disappeared into the wall of the mortise which was why I couldn’t find it upon initial inspection. Needless to say it was quickly and easily removed and my joint slid home with no gap at all. Fitting this joint was interesting because it forced me to work through all of the possible snags you can encounter and this serves as a handy reminder for troubleshooting in the future. Usually something like this is solved very easily once the mystery is figured out and the mask is removed from the monster to reveal that it is actually Mr. Winston who runs the old carnival.

Mystery solved by those dang meddling kids in the groovy van once again.

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