Wide tenon question...

From all my reading I know that a tenon shouldn't be longer (I may be using the wrong dimensional term) than 3 inches. However, exactly what does splitting a tenon into 2 smaller tenons accomplish? I know the goal is to prevent wood movement of the cross grain/long grain interface from stressing the joint, but if you make 2 tenons each 3 inches long for a total of 6" worth of tenon, HOW does that prevent joint problems? Is it the same principle by which a box joint works?
dave
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Dave,
The best way to answer your question is to point you to FWW #165. They have a "fantastic" article on wood movement with suggestions on how to avoid joint failure with various techniques. They go into great detail discussing the exact problem you're describing and give multiple solutions for solving it. The pictures especially are helpful.
As a side note, the same issue has another article on rough milling your wood prior to final milling and assembly with wait times to allow the wood to neutralize its stress movements after major cutting takes place. This was probably my favorite article in a long time. I've tried all the techniques on my current project (an end table) and it's so much easier to do things this way. Well, for a hobbyist anyway, I'm sure production shops don't have the time for stuff like this, but I certainly do.
Mike

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Mike, thanks for the timely reply! I DO have 165. How do you locate the articles? I have about a dozen FWW issues, but no facility for finding a WW tip quickly. My memory isn't sufficiently sharp to remember that any issue I own addresses my current questions!
page 47 shows apron tenons and the use of pins. Is a pin made of hardwood dowel, and then you need to use a plug cutter to cut a matching or contrasting piece of wood to cover the hole? Looks like gluing just a portion of a long tenon would be simpler than making two mortises/tenons...
dave
Mike in Idaho wrote:

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Dave, Hmmm...you make it sound like I have this amazing memory -- hee, hee, my wife would beg to differ with you. It was pretty easy because 1) I've only subscribed to FWW for a year now 2) it was my favorite magazine and I read it about once a week (yeah, I'm a freak, I know), and 3) I had just sent a copy of that same article to a friend to convince him to subscribe to the magazine (oh, and I sent him the rough milling article too to convince him to buy a bandsaw instead of an Incra fence for his tablesaw, but that's a whole 'nother story).
As for what I do, I can only tell you what I "plan" to do (haven't done it yet). I have 7" aprons on the bottom of my end table and the sides (and back) have 5 7/8" tenons that will sit in a 6" mortise (to expand down like the article indicates). I'm putting in 3 1/4" pins starting 1" from the top of the tenon and spaced 2" apart. The hole for the pins in the tenon will be 1/4" for the top one and then elongated 1/16" top and bottom in the middle pin hole and 1/8" top and bottom on the bottom pin hole. I only plan to glue the top 1/3rd of the tenon into the mortise.
As for materials, the piece is a distressed country pine so any hardwood will do (probably poplar/pine/fir whatever the standard dowel material is). I just plan to plane it flush and I'm using Zinser's amber shellac as the color/finish with an antique brown wax over that.
I suppose you could cut your own plug if you actually wanted to hide it, but I want it to show. Another technique is to use a square pin in a round hole (it wedges itself in really well). In fact I read an article in wood mag one time that said he used square pins and when he cut the hole in the tenon he cut it a 1/32 or 1/16 of an inch back from the hole in the mortise so when the pin was driven through it would pull the tenon tight into the mortise and he didn't even bother with glue (some professional antique pine furniture maker wrote the article). I thought that was interesting too.
Oh, and on top I'm using 1/2" (from 8/4 stock) for a panel configuration (rails/stiles) and I think I'm going to skip actually pinning the tenons since they're small enough, but I'm going to use my hollow chisel mortiser and cut 2 fake pin spots and put in chamfered (proud of the rails) square pins in a dark contrasting wood just for fun. My point being, there's a number of ways you could go about it, just depends on the look you want, refined vs country, vs whatever. Kinda fun :)
I have no idea how that will hold up, but I figure if the experts do it and that's how it was done in golden times, it ought to work just fine.
Mike

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Mike, you could have left me forever in awe of your "amazing memory"! :) We are just too honest for our own good, sometimes, huh? <g>
anywho, thank you for the details of your table. I DO remember recently reading about offsetting the pin holes to draw the joint TIGHT and that sounds like a good idea if I can do it without "over" doing the offset. The square peg in a round whole technique's another story; can't remember reading that one.
Have you ever done wedged tenons? I came across an article that countered my newbie perception that the wedge was placed into the tenon length-wise. I should have started this WW thing many years ago, so that I won't die before I can learn 1/10 what I need to "do it right". <g>
Please post some pics once you get that bad boy going!
dave
Mike in Idaho wrote:

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Dave mentioned, Mike replied:

Yeah, but if I'm going to suffer guilt, it better be something really worth it, right? :)

I'll let you know how it goes when I try it. I'm always nervous trying something new, but once I've done it (and usually screwed it up) I get it down pretty easily after that.

I've noticed that a number of furniture stores (RC Willy for one) in our area is starting to use this technique a lot. I'm sure they do it more for looks than function, but apparently it holds the pin tighter in the hole. You shave the front of the pin semi round so it goes in easy, but the top part is square to act more like a wedge.

I'm going to try this for the base of my neander bench I plan to build (as soon as I finish the coffee table for SWMBO).

I kind of feel that way sometimes, but it's been 1 1/2 years for me so far and between projects, Norm, Roy, the Library, the wreck, Woodsmith, and FWW I think I've come a long way. In fact, the best example is when I finished 3 benches for my siblings for Cmas and my mother-in-law came in to check them out and her comment was "Wow, you really can do this!". Nice.

Will do.
Mike
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There are three ways to find FWW articles. Memory - not practical for anybody over 50. Next, there is an online index at the FWW site. Third, there is a booklet with an index up to #120 (I think that is correct). You can purchase it from Taunton Press. I have it and find it very useful for finding old articles.
Len
Bay Area Dave wrote:

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thanks, Len. I'll check out the FWW site for the index, as that would be my best solution.
dave
lopez wrote:

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<SNIP>
Go here http://www.taunton.com/cgi-bin/artresult-fw.cgi to find the FWW index to all articles in all issues.
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Hey Dave,
A double tenon also gives more glue surface. I use them on chairs when stock thickness permits.
Cheers,
Andy
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A Dubya wrote:

... and I've been experimenting with multiple small (through) tenons for drawer joints. I've put up some drawings and photos of my first efforts at: http://www.iedu.com/DeSoto/jigs.html
--
Morris Dovey
DeSoto, Iowa USA
  Click to see the full signature.
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If you split a 6" tenon into two separate ones, the expansion distance is reduced by one half! Plus, you get additional joint strength from the additional area contact. Of course, you have to make two mortises instead of just one.
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