wide apron wood movement

[Stan Calow]

How would you glue up a leg joint with two tenons on a wide apron (7 1/2") to count for wood movement? I estimate 1/8" shrink/swell across the apron and planned two tenons rather than one long one. But now I am unsure whether to glue both tenons, just the top one, or something else. Please advise. Mortises are already cut so I don't want to make radical change.

apron.jpg

[John TenEyck]

That's a pretty common situation for the bottom and lock rails on passage doors, both interior and exterior. Bottom rails are usually even wider. I had the same concerns when I started building doors but have never had a failure doing it similar to what your drawing shows. I've have always used full glue coverage on the tenons, with Plastic Resin Glue, TB III, and epoxy over the years. No failures yet.

In your case, I would fit the top tenon snug in the mortise, but cut the bottom one narrower to allow for the expansion/contraction you expect seasonally, and glue it with TB or similar glue.

John

[Stan Calow]

Thanks John. Good advice as always.

[Wayne Lomman]

John has it pretty well covered. I think you may be worrying a bit too much about movement. A well seasoned piece of timber is not going to cycle that much for the rest of its life unless you leave it unfinished out in the weather. Cheers

[John TenEyck]

The OP didn't say what species of wood he's using, so I picked red oak and plugged it into the Shrinkulator on Woodbin, using a moisture range of 6% for the Winter and 12% for Summer, about what you would expect here in the NE where I live in a house with no AC. It returned a result of 0.15" for tangential movement, 0.07" for radial. This is consistent with the OP's estimate; drop the RH to 11% in the Summer and it's even closer. Will it really be that much? I can't say but I've seen lots of problems over the years like split floating panels that probably weren't floating as well as the builder thought, cracked door frames from panels that swelled, etc. I saw this door this morning at my lumber supplier's office.




The office was built by them 3 or 4 years ago. The doors are QSWO with stave core stiles and edge glued solid panels. This is an interior door that is open 95% of the time, so the RH should be pretty uniform on all sides. The door is stain and clearcoat on one side, white lacquer on the other. I didn't see any heat/AC vents nearby but didn't look too hard so I can't say for sure. The door was fine when I was there last Fall. Now you can see where the lower panel has cupped, badly, and broken the retaining moldings away from the frame. There are 2 or 3 other doors just like within 15' and they are fine.

Wood moves, sometimes quite a lot.

John

[Stan Calow]

I am the OP. The wood is black walnut. Yes, I agree I worry too much about things like that, but I thought there was a reason for using two tenons, and then couldn't figure out how that helped with wood movement since the whole apron would still be 7 1/2 wide and subject to movement.I used one of the on-line calculators to get 1/8 ". I do understand the reason for leaving the bottom tenon less than snug.

[John TenEyck]

Stan, I think the primary reason for using two, narrower tenons is so that the mortise doesn't become so long that the sidewalls bow open if the RH changes. For this reason, breadboard ends are attached using castellated tenons, rather than one wide, long one.

John

[Wade Lippman]

so I picked red oak and plugged it into the Shrinkulator on Woodbin, using a moisture range of 6% for the Winter and 12% for Summer,

With humidifiers in the winter and A/C in the summer I don't think you would see much of a moisture range at all.

15 years ago I made a small organizer out of bubinga with tightly fitting curly maple drawer fronts; but realized the curl would be going the wrong direction if I matched grain directions properly. I said the heck with it; if there is a problem I will deal with it later. There are no gaps in the winter, and they don't stick in the summer; so there is very close to 0" movement.

My wife bought an expensive cherry table 5 years before I met her, 35 years ago. I looked it over and saw they mixed grains with no provision for movement. Haven't had a problem yet.

So I think the concept is overrated.

[Stan Calow]

Thanks for all the input. John, I do a lot of breadboard ends so that makes perfect sense. .

[William Young]

Stan, Consider that you really don't have exp/contr. concerns over the full 7 1/2". If you subtract the spaces at the top and bottom between the apron edges and the tenon edges, you will have substantially less (judging from the proportions of your sketch). Particularly if your finished project will live in a climate controlled environment, I would glue it and go. If you want to play it safe, just glue the half or 3/4 of the the tenons closest to the center of the apron. In hindsight, I think I would have left the center portion of the tenons and just glued the center 3" or so. I suppose, if you wanted to go to the trouble, you could retofit a loose tenon and then glue just the center. That might add a little strength but not sure it's needed.