Author Topic: Tennons on a wide board  (Read 13930 times)

dkeller_nc

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Re: Tennons on a wide board
« Reply #15 on: February 20, 2007, 08:28:38 AM »
Comment/question on gluing the bottom tenon rather than the center or top tenon.  If you glue the bottom tenon, wouldn't you have to leave a 1/4" gap or so between the top and the side?  Otherwise, in the humid conditions of the summer, I would expect the sides to expand, and since the expansion will be at the top (since the bottom is glued), I'd expect the sides to exert force on the top, possibly warping it or causing compression failure in the sides that would then show as cracks when the piece dries out in the winter.

I'd think such a gap between the top and the side would be very unsightly, and while it could be covered by a molding, the molding itself would have to be somehow mounted to "float" across the side, possibly by being simply nailed on (no glue).
Period Furniture & Carving as a hobby - about 20 years woodworking

Antiquity Period Designs, Ltd.

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Re: Tennons on a wide board
« Reply #16 on: February 20, 2007, 10:20:04 AM »
Gluing the center tenon is the best so that the board moves in equal directions from the center.  However, if you glue the center or upper tenon the expanding/shrinking of the lower tenon could cause the knee block to separate and fall off!  If you glue the bottom tenon, like I do, leave a slightly larger gap at the top if you make it in winter, or a smaller gap if you make it in summer.  Apply a dark stain to the edge before you apply to molding.  I will also glue and screw a cleat across the top of the inside leg posts to keep the upper section tight. 

In 21 years of doing this type of construction no customer as ever complained of the gap at the top of the board side especially when I explain to them why I do it. (When I was an apprentice the boss told me to make the job so it does not come back for repairs.)

Dennis Bork
Antiquity Period Designs, Ltd.
Professional period furniture maker since 1985.  Received a B.S. degree in physics then apprenticed and worked as a wood patternmaker for 12 years. Cartouche recipient 2009. Retired Dec. 2018.

HSteier

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Re: Tennons on a wide board
« Reply #17 on: February 20, 2007, 03:52:33 PM »
My two cents.

Real furniture made out of real wood moves. You just need to decide where you want to have the movement.

Howard Steier

dkeller_nc

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Re: Tennons on a wide board
« Reply #18 on: February 20, 2007, 04:18:21 PM »
Well - that was sort of my point about selecting where the wood movement will be.  I note that on many antiques, there have been some repairs identified to the knee blocks, and I wonder whether what Dennis states is exactly the reason - on antiques the center or upper tenon was glued and/or pegged, so the knee block was broken loose over time. 

On many antiques, the knee block was also nailed as well as glued, so perhaps the nail was an effort to keep this from happening, since the nail will flex a bit when the side applies pressure.

My leanings are exactly as Dennis recommends - my reasoning is that on a dressing table, the top is usually made to overhang the sides quite a bit, so a small gap at the top of the side will not really be noticeable (except to us furniture geeks that get down on all fours to examine an authentic original!)
Period Furniture & Carving as a hobby - about 20 years woodworking

HSteier

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Re: Tennons on a wide board
« Reply #19 on: February 21, 2007, 09:55:57 AM »
One minor correction.

"Geeks" fix your computer.

"Nerds" get down on all fours to examine furniture.

Howard Steier

dkeller_nc

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Re: Tennons on a wide board
« Reply #20 on: February 21, 2007, 10:20:02 PM »
Ha!  Correction noted and agreed to.  It's a shame more customers aren't so interested....
Period Furniture & Carving as a hobby - about 20 years woodworking