Greetings.
I’m making a piano bench and mistakenly cut my leg mortises too deep. I often hear that woodworkers leave a small space at the bottom of the mortise for glue squeeze out. Some people say 1/16” space, others 1/8”.
my question is, if it’s more than that (say a fat 1/4”), is any harm done?
thanks.
– Hobbyist
Replies
No harm at all. All the strength is in the cheeks of the tennon to the walls of the mortise, ie a through tennon joint.
Thanks MillSt, makes perfect sense (I didn’t consider the case of a through tenon). The legs are beefy (almost 2” square at top) and the tenons will have lots of cheek (~ 1” long by 1.75” wide), so I think I’m looking good.
This happened to me on a recent project. I cut pieces to fit and glued them onto the bottom of th mortise to take up the extra space and get the depth that I wanted.
In the old days, with not very dry wood at construction time, folks worried about empty mortise areas, esp. much larger than your 1/4", as the leg wood could shrink and cause a slight depression over the empty space. However, I don't think you have a problem here. If you remain worried, use phantomtrapper's suggestion.
I'm finishing up re-gluing an 86 year old table and chairs set. Every single mortise and dowel hole was over deep. FWIW.
“[Deleted]”
Why not use epoxy?
You must fill the space. Be sure to use the same species and match the same grain direction as the tenon. Start by sawing out a piece larger than you need, say 1" in width, depth and length. Set it on small stickers in your shop. Mill 1/16" of each dimension removing equal amounts of material from each face and turn it in the stickers for the next 16 days finally reaching finish size. Dry fit into the mortise and move into its final destination for two weeks. You may then glue into place, and continue your build.
Wow, Rob!!! You are much more meticulous than I. I had a scrap of something or other the right thickness, cut them to size, rounded the corners, and dropped them in. I know, I should have squared the corners of the mortises but I am lazy that way. My rasp is faster than my chisel, and time is money. 6 mortises, 15 minutes max, I was gluing the tenons in. Mind you, I do screen my phone calls in case it may be the fellow calling to tell me it has fallen apart and he is appalled at such shoddy, haphazard work.
Now we can both take our tongues out of our cheeks. Happy New Year.
Don't forget that it's always best to use wood that came from the same forest and was cut by the same person during the same lunar phase. If you aren't sure, it's best to contact your lumberyard and ask them for the date that the wood was cut and the name of the person who cut the tree down.
Remake the tenon piece(s) and make the tenons longer for additional strength. Stiles and rails usually don't represent a lot of wood, and are parts usually very easily remade.
You're making a piano bench. A seating project. This isn't an occasional table. It'll have to hold one's entire weight. I'd call it a fortuitous error that allows you to have longer tenons by remaking the four rails.
I agree with #1, as long as the mortise and tenon are designed properly for the project, the dead space in the mortise will have no effect on the joint strength. A M&T joint will fail when something pulls it or twists it out. The dead space will have no effect on that.
I agree, the first answer clearly explains how a through M&T joint is the perfect example of having no connection between the bottom of the tenon and the bottom of the mortise, and it is a strong joint. Even if you fit the joint perfectly and glued it, it would be an end grain to face grain joint and add little if any strength. It's far more important to have a snug fit between the cheeks and the sides of the mortise.