Detailing for wood movement - Mission cocktail table

[Gene Davis]

The lower shelf in this Stickley design looks like one large glued up panel that butt-joins, endgrain to long grain, to stretchers, and two through-tenons are used in the subassembly.

Look at the photos and you'll see.

Sure looks to me like a problem waiting to happen, unless those cross pegged tenons are faux.

How would you handle this?

Here's my idea. The tusks with pegs are faux. The shelf panel has one large tenon at each end, tenon length 1/8, with 1/8 shoulders all around. The tenons fit to same-sized mortises in the sides of the stretchers, but cut with 3/32 extra length at each end. The shelf panel fastens to the stretchers with blind loose tenons (dominos) with the two at center tight and glued, all others in over width mortises and not glued.

[Gene Davis]

I should have said that fit and size at ends is initially determined by moisture content and season of initial build. You are building tenons and mortises with same logic as for breadboard ends.

[Jamie Buxton]

Or make the tenons somewhat narrower than the mortises through the rails, so there's room for the panel to change width without stress. No faux required -- just revealing what wood actually does.

[Kent A Bathurst]

Or make the tenons somewhat narrower than the mortises through the rails, so there's room for the panel to change width without stress. No faux required -- just revealing what wood actually does.

That's what they did - cannot see it from that photo, but the tenon is smaller than the mortise - there is a gap. Or, at least, there should be. You have to allow for those tenons to move out and back.

The pegs keep the shelf tight to the stretchers, but will "slide" against the stretcher as the shelf moves to and fro.

No need to make "faux tusks". Certainly not how the original stuff was made.

Make tenons and through-mortises, allowing for expansion. In this A+C joinery, with through-tenons, you have to step back from your [my/our] natural tendencies to have the mortises fit tightly in the tenons.

[Gene Davis]

Thanks! Glad I asked. Will take a really close look at one as done by the Masters of Manlius before finalizing my details.

I had thought of the tenons and over-width thru-holes and no glue, all meant to slide to and fro between January and July, but then complicated the detail with glued-on ears on the tenon projections to mask the slide gaps.

But hey, those gaps are bound to be pretty small. With QSWO and the piece built to live in Denver's climate, I'll bet there will be only 1/8 or so of total movement each side. Best way? Build and finish the shelf in January, measure and mark for stretcher cut but wait until July and then re measure and make holes then.

In the interim, build all the other pieces I am planning.

[Kent A Bathurst]

Thanks! Glad I asked. Will take a really close look at one as done by the Masters of Manlius before finalizing my details.

I had thought of the tenons and over-width thru-holes and no glue, all meant to slide to and fro between January and July, but then complicated the detail with glued-on ears on the tenon projections to mask the slide gaps.

But hey, those gaps are bound to be pretty small. With QSWO and the piece built to live in Denver's climate, I'll bet there will be only 1/8 or so of total movement each side. Best way? Build and finish the shelf in January, measure and mark for stretcher cut but wait until July and then re measure and make holes then.

In the interim, build all the other pieces I am planning.

Gene -

To be pragmatic about it, those thru-tenons look to be only 2" wide +/-. For something that narrow, the expansion on QSWO will be much less than 1/8" total. Also - If you let the rough lumber acclimate in your shop for a couple weeks, or even rough cut the parts and do the same with them. Then - you have "Denverized" everything, and you don't have doodly-squat for RH changes thru the seasons.

Then you can co whatever you want - tight fit , glue, whatever - there is not enough happening there to worry about, IMO.

But, "best practice" is to leave some room for movement. ON wider joints [a lot of A+C stuff has, say, 6" - 8" tenons, either blind or thru] you need to pay attention to this issue.

SOmething to consider - will the piece always live in Denver? DO you care what happens to it if it leaves the Front Range?

I built a 44" x 86" dining room table, QSWO, with breadboard ends. LIved in Atlanta for a couple years. It moved to St Louis. It turns out - the winter RH in ST Louis must be darn near nuttin'. We will be going to visit them [former neighbors, and good friends] for Thanksgiving, and I am taking tools, clamps, etc., because the doggone thing contracted so much that the outer pegs in the breadboard ends [through elongated holes in the tenons] did not move enough, and we gots us splits in the table top at all 4 corners, right at the outer pegs. Gotta do some surgery.

Lesson Learned: "So - wise guy - you think you've got this movement thing all figgerd out? Are you sure? What harm will it cause to elongate those holes by another 1/4?"

Yeeeeshhhh...........

[Gene Davis]

It's not the tenons for which the thru-holes are cut wide to accommodate movement, but the 36" wide glue-up of boards the tenons are a part of. I'll draw up a study of it all in Sketchup when we get set here with broadband and WiFi.

[Kent A Bathurst]

It's not the tenons for which the thru-holes are cut wide to accommodate movement, but the 36" wide glue-up of boards the tenons are a part of. I'll draw up a study of it all in Sketchup when we get set here with broadband and WiFi.

Oh - Duh. Of course. I did not think it through all the way. Yeah - you are going to be facing a lot of movement there.

Have you checked out this tool?: http://woodbin.com/calcs/shrinkulator.htm

The hook[s] are: (a) you gotta be able to pick your numbers, high and low, and (b) it may overstate the severity, but that is anecdotal.

I think your biggest issue[s] will be (a) getting your rough wood acclimated to your climate before you machine it - QSWO usually comes from PA and environs, in my experience, and (b) deciding if it is designed exclusively for the Front Range, or if you want, say, New Orleans' humid summers included in the potential habitat.

[Gene Davis]

And here it is as modeled by me using Sketchup. I did not model in the over-width through-mortises in the lower rails, but I will after I decide how much.

I gave a slight tilt to the legs as can be seen in the orthographic side view. It is 39 x 39 x 17 high, and I will make it in QSWO. Joinery will be dominos for the leg to apron and leg to rail joints. Tiles from a place in Minneapolis that has stuff that looks like what Stickley uses. I will buy a sample 4x4 in one of their greens before committing to the batch of 25 6x6 tiles.

For you SU users, it is up on the 3D Warehouse site. Search "cocktail table mission" and you will find it.

[Kent A Bathurst]

Looks good.

With a shelf that wide, you may want to consider another tenon in the middle - support that long span a bit more.

Or - you could put cleats under the shelf, along the stretcher - between the 2 tenons. Will never be seen.

Photos when you're done. please - I like the design.

[Gene Davis]

There will be a pair of blind tenons near the middle, maybe 4 inches apart. Dominos, you won't see them. They will get glued, nothing else will. QSWO won't move too much over the 4 inches.