Mitered Table Top

[Robert Michelson]

I have a student who really wants to make a cherry table top as pictured below and I have not been able to talk him out of the huge miter joint. He wanted to simply glue the miter joint and that was all. He does not want an apron around the perimeter, and would like to install the legs with steel leg plates and hanger bolts.

I have talked him in to some kind of apron under the joint to stiffen it, to add a leg under the joint, and to use biscuits or dowels to reinforce it (we don't own a domino). But I am still not convinced that will help enough to overcome the tendency of the miter joint to pop apart with seasonal change.

Countertop Draw bolt? 1/2" Plywood plate under the entire table top? Any ideas are welcome.


Miter Table lndscp.jpg

[Bert McMahan]

You could use plywood to make basically the whole table, then do the miter with thin veneers. Depending on your resaw capability you could glue up a stack of boards and resaw it to make some multi-board veneeer "sheets". Maybe the outermost edge could be solid so you can get a seamless wraparound look without having to match veneers at the corners.

[andy bessette]

You could glue a spline down the length of the miter, or glue and fasten a wide batten to the underside.

[Jamie Buxton]

If the table is freestanding, the miter might not come apart as the wood shrinks and expands. If you run through the math, it turns out that the hygroscopic movement acts to change the angle between the two legs of the table. That is, it might be a perfect 90 degrees when you build it, but when the wood shrinks the angle gets smaller. When folks build solid-wood L-shaped built-in counters for a kitchen counter, that miter joint is in big danger, because the miter angle can't change. In a freestanding table, you might be okay.

If you put a sheet of plywood under the solid lumber, you must allow the solid lumber to move independent of the plywood. The plywood does not grow or shrink like the lumber.

[Mel Fulks]

I like the spline idea. Make the splines with the grain going the short way, and at least a 1/16th narrower than the groove.

[William Fretwell]

When the table expands the 45 degree angle moves outward from both sides opening the joint. Only veneer on a dimensionally stable substrate will maintain it’s position.

[Phil Mueller]

Hate to be this way, but sometimes folks just have to learn lessons the hard way. Good options above; best in my opinion is plywood or mdf and veneer. If the student chooses solid wood, then likely someday he will say to himself,
“well, Robert was right”. He’ll still learn skills putting it together.

[Robert Michelson]

Thanks to everyone for your ideas. The students keep finding designs online from Wayfair and such that show miters and framed herringbones and all kinds of things that probably work great with bricks but not so good with wood. I am tempted to buy one of them just to see how it behaves.

He really wants solid wood so I am leaning toward a spline in the joint and a wide batten underneath with elongated holes to give it some strength but allow for mobility. I am also trying to sell veneers over mdf, but what I REALLY want is to talk him out of this idea.

[William Fretwell]

Think about glueing the splines at the middle of the table only, leaving the rest of the spline pegged but floating.
Ask him to do a simple drawing of the table top, then draw in again with 3% expansion. Have him calculate the change in size and the widening of the gap at each corner, at least he will know what he is getting into. Simple maths explains a lot to those who will listen.

[Gary Ragatz]

You could use a half-lap joint along the miter. The top might split somewhere, but I'll bet the miter won't open up.

[andy bessette]

...what I REALLY want is to talk him out of this idea.

He will learn much more if you don't.

[Mel Fulks]

It's not a picnic table and I doubt the guy lives in an unheated and non air conditioned cabin...or tent. Some get educated
and feel they are smart enough to break some rules. And some experiment and get educated by breaking some rules.
A wood Edison would be good.

[William Fretwell]

The grain would be at 90 degrees! Not going to last long at all.

[Kevin Jenness]

The design as shown in solid wood will be fine if the joint is re-enforced with splines (biscuits, Dominos, etc), supported under the joint and allowed to move. If there are no legs under the joint the longevity of the table will depend on the soundness of the joint and the stress put on it. If the legs are located near the ends the structure will be unstable and easily tipped by any weight at the outside miter corner. A mockup would be advisable.

Any substructure should be fastened with flexibility in mind (buttons in a groove, elongated holes) as with any solid wood top. The angle will change with seasonal changes in MC. If dimensional stability is required it should be a veneered panel.

[Mel Fulks]

The grain would be at 90 degrees! Not going to last long at all.

The great Ripley Believe It Or Not Museums have a lot nuttier stuff. Parquet floors last pretty well ....but some of the
stone floors in Pompei and Herculaneum are showing a lot of wear !