Gluing tenons on widish board

10%?

Mark Mandell - Gone Round In New Jersey

Unless this is deck furniture subject to rain, your EMC will not change by 10% range, especially for finished furniture in a home. 2% (3 max) Summer to Winter is more realistic. I have a number of breadboard tables in cherry, ash, and sycamore and edge registrations change across a 30" top are never more than a 1/16" usually less. I think your over-calculating things.

Re: Gluing tenons on widish board

Sgian Dubh

I suspect you're over-estimating likely percentage points moisture change. It's probably more likely to be between about 5 and 6 percentage points annually, somewhere between about perhaps 6% MC (winter) to perhaps 11 or 12% MC (summer) in a residence. I'm basing those numbers on UK homes, so your numbers in the US (I'm guessing) might be a bit different.

In soft maple this equates to a maximum possible change in dimension in a tangentially sawn board of less than 1/8" i.e., 2.7 mm because I work these numbers out in metric measure. In reality, any expansion and contraction is likely to be less than even that for a number of factors I won't detail here for reasons of space, and perhaps a bit of laziness on my part.

So, forked tenons? In your case I'd glue the top fork to keep the top edge of the rail in line with the top edge of the leg. I would probably also add a bit of adhesive to the top quarter of the lower tenon so that the bottom 3/4s of the tenon can wriggle about a bit in the mortice which would be cut slightly longer than the tenon's width. As to pinning or pegging, all you'd need to do would be make the hole in the lower tenon slightly sloppy, easily achieved by wriggling the drill and the bit you use to bore the holes backwards and forwards a little across the tenon's width.

As to choosing to pin or peg these joints, I can't see a technical reason for doing so in a well made M&T of this size and form in relatively small tables like this that aren't going to see much stress unlike, say, an architectural door, unless it's primarily for decorative purposes, a choice that could be justified, perhaps on aesthetic grounds. Slainte.

What I did...

Barry Irby

Made a sideboard a few years ago. The rails on the ends are about 14" wide. I divided them into three pieces. About 3" top and bottom and a center piece about 8". The pieces are T & G and have a bead to disguise the join. The grain was carefully selected to make it appear they all came from one wide board.The top and bottom rail are mortised and tenoned into the legs and the center piece is free to move in a slot in the leg. This was quartersawn heart pine. I have never noticed any movement in at least ten years.

Re: 10%?

Michael Foster

Thanks Mark. I was looking online and found the 10% online, but I also saw a 3% figure on another site and I just went with 10 for worst case scenario. I would think you are right and will go with a much smaller leeway.

Re: Gluing tenons on widish board

Michael Foster

Thanks Sgian. I appreciate your suggestions. I only make furniture for our home, so I don't do a lot. I knew there was a chance for the apron to move, and I didn't want the joint to fail. It is an end table, so won't take any abuse. I was thinking of pinning the joint for esthetics and just a little added insurance but now that you have discussed it, I may forgo that. I will make the tenons just a bit smaller than the mortises and glue as you suggested. That was on par with my thoughts. Thanks again.

Re: What I did...

Michael Foster

Ahh, this is similar to what I did several years ago with another pair of end tables that had a wide bottom shelf. I used breadboard ends to allow for movement. Thanks.

Movement

Mark Mandell - Gone Round In New Jersey

Mike,

To calculate wood movement you need 3 things:

1. Initial Moisture Content

2. Final Moisture Content

3. Wood species

Just keep in mind that a 4% change in MC doesn't translate to a 4% change in dimension.

pinning the joint for esthetics

David Yoho

Should you decide to not pin the joints but would still like the look, you could always drill the legs with a shallow hole and insert a plug.

Re: Gluing tenons on widish board

Dick Coers

Maybe the others know where you live, but I couldn’t make the decision about seasonal change without that knowledge.

Re: Gluing tenons on widish board

Michael Foster

Vermont. We do get a pretty wide swing in humidity but the humid months don't last long, maybe 2 or 3 months.

Re: Gluing tenons on widish board

Dick Coers

Thanks for the info. Running a wood stove would be what I consider my first thought in Vermont. That'll run down the humidity pretty well. In Central IL I've always built to allow for 1% of wood movement. At that, a 12" board would move 1/8". Been building furniture for 48 years now, no cracks.

Wide tenons

Ellis Walentine

Hi Michael,

I'm late to this conversation, but I'd not think twice about pinning the tenons, for aesthetic and structural purposes. It's quick and easy enough to elongate the holes in the tenons to allow for some wood movement. Be sure to allow some extra room at the ends of the lower mortises for the apron to shrink or expand slightly. I also agree with Richard about gluing the top tenon and letting the others float.

An alternative to having a front apron would be to let the drawers run the full width of the front, with stretchers above and below to connect the legs.

Cheers,

Ellis

Re: Wide tenons

Michael Foster

Thanks Ellis, that is exactly what my design is for the tables. I will probably pin them, but may go the extra distance and make them square pins, maybe using a contrasting wood.