Tennons on a wide board

M

maskws

Well-known member
Didnt take me long to get to my next question on a Queen Anne Dressing table; the ends of the table are a 14 inch wide board (grain running horizontally) which I will put 3 tennons on to attach to the legs. My question is I presume you only glue the bottom 4" tennon and pin the upper two?

martin
 
Martin,

I will glue and pin the lower tenon but use elongated pin holes on the other two tenons and no glue.

Dennis Bork
Antiquity Period Designs, Ltd.
 
Martin,

I have glued and pinned about 4 " of the center tenon  and used elongated pinholes on the other two tenons.

  Jim Vojcek
 
Both my method and Jim's will work.  However, I glue the bottom tenon because the knee block is glued to the bottom of the side and it could break loose with wood movement.

When I was an apprentice the boss said, "make the job so it does not come back for repairs."

Dennis Bork
 
Thanks Dennis.  Always nice to know the reasons why you do something, and I never thought about the knee bit.  Martin
 
I have questions about the above technique. I assume you dry fit and clamp the legs to the side and then drill through for the pins. Do you then separate the pieces and file to elongate the hole in the tenon?
Do you get separation between the leg and the apron as the wood dries out, in other words do you eventually get a visible seam along the leg-apron join?

Howard Steier
 
If you're draw boring for the pins, you first drill the hole before dry fitting/clamping. Then you dry fit and mark a spot on the tenon slightly, say 1/8", further from the shoulder, drill out the tenon, then dry fit and clamp and insert pin when you're ready. This will pull the shoulder tight.

Pam
 
Do you also elongate the hole in the tenon in the North-South direction to allow for wood movement in the apron? When you drill the tenon hole 1/8 closer to the shouilder, does the peg ever split the tenon or mortise when driven in?

Howard Steier
 
Howard,

This is what I do - dry clamp the legs and side together, drill for the two pins hole that will be egongated, knock it apart and then elongate these tenon holes across the grain, re-assemble and glue the bottom tenon and mortise, then drill the hole for the non-elongated hole and hammer in all three pins.  I will also glue and screw a cleat/tie bar across the inside tops of the two cabriole legs.  This will help hold it all together - just incase "Murphy" flies over.

If you are using 1/4" pins and the draw bore method, drill the holes in the tenons closer to the shoulder by only 1/64-1/32" max.! 1/8" is way too much as your pin is only 1/4" and it will split apart so you will be left with only a 1/8" pin holding the joint together.  You may also find the pin mushrooming as it is driven in.

Dennis Bork
Antiquity Period Designs, Ltd.

 
Antiquity said:
...
If you are using 1/4" pins and the draw bore method, drill the holes in the tenons closer to the shoulder by only 1/64-1/32" max.! 1/8" is way too much as your pin is only 1/4" and it will split apart so you will be left with only a 1/8" pin holding the joint together.  You may also find the pin mushrooming as it is driven in...
Click to expand...

Thanks, Dennis. Sorry about that guys, should have said: I have a couple of draw bore rods/pins to do most of the work rather than relying on the strength of the insert to pull the tenon; I relieve the shoulders so it doesn't take that much force to hold it once the initial compression is done.

Plenty of experience here, Howard, otherwise wouldn't have offered advice. Also, I got my initial 1/8" from Kingshott.

Pam
 
Pam,

I've never seen a draw bore rod.  Can you tell me the diameters and length of your item.  Perhaps a photo.

Thanks,
Dennis Bork
 
The diameters start small, blunted points, and taper to larger; but my pins are eccentric. That way, as you push and turn the tenon is drawn into the mortise. I'd normally be happy to take photos and measurements, but most of my stuff is still packed. I think mine top out at between 1/2 and 3/4 inches.

I tried to find photos, but none of my standard old tool vendors have any for sale right now. You might want to check on ebay. I think Joel at ToolsForWoodworking.com offers a set, but couldn't find any on that site either. Chris Schwarz of Pop Woodworking did an article on making them in the Aug, 2005 Woodworking magazine; but he made concentric pins, which get you most of the way there. There's also a pin sold by Craftsman, very cheap, like $6, but I doubt it's eccentric. And there's an article on Woodcentral ( http://woodcentral.com.ldh0138.uslec.net/cgi-bin/readarticle.pl?dir=handtools&file=articles_669.shtml ) that's a review of following Chris' instructions. The ones they made may be sized better for the work Howard's doing. Here's ( http://woodcentral.com.ldh0138.uslec.net/cgi-bin/archives_handtools.pl?read=85827 ) a discussion on Woodcentral. And, finally, here's John Alexander's discussion at Green Woodworking ( http://www.greenwoodworking.com/Drawbored%20M%26T%20Joint.htm ). I suspect he'll talk about this extensively at Colonial Wmsburg.

I called them rods because you guys called the inserts pins, but they're really called draw bore pins and the inserts are pegs.

Pam
 
Jumping in months late here, but . . .
What about the method Jeffrey Greene discusses in his book, wherein he pre-compressed the wood in the width before gluing up all 3 tenons.  I'm about to assemble the sides on a highboy and am wondering whether to try this method or to stick with the pin method discussed here.

Thanks,

Herman
 
Do not clamp the wood to compress it.  Like a fool I experimented and tried this method on a highboy for a customer.  About 9 months later the highboy came back to my shop because the sides all cracked and split.  I had to replace the two sides.  Use the method that I posted below.  (I can't believe Jeffrey Greene would even suggest this method.  I can't believe I was foolish enough to try it!)

Dennis Bork
Antiquity Period Designs, Ltd.
 
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).
 
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.
 
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
 
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!)
 
One minor correction.

"Geeks" fix your computer.

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

Howard Steier
 
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