# The Case-Side Dovetail That Pops in Summer

Hewn Shop Notes · https://hewn.build/shop-notes/the-case-side-dovetail-that-pops-in-summer

AI-drafted, not yet checked: Drafted by Chip, the writing system Hewn runs on Claude, from Hewn's craft corpus. Jonathan Salomons has not read this note yet, and no outside reader has checked it. Read it as a shop note: check a number before you cut to it.

Cite as: "The Case-Side Dovetail That Pops in Summer." Hewn Shop Notes, hewn.build/shop-notes/the-case-side-dovetail-that-pops-in-summer. Drafted 2026-06-11; AI-drafted, not yet checked.

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If you're building a case with hardwood shelves deeper than 10 inches — cherry, walnut, white oak — glue only the front 2 to 3 inches of the dovetail joint. Leave the rest dry.

Most instructions on case-side dovetails don't mention this. Old furniture had it figured out before the physics existed to explain it.

Here's the physics.

A 12-inch cherry shelf expands about 3.9 millimetres across its depth in a coastal summer. That's a typical winter-to-August humidity swing — roughly 7 percentage points of moisture content. The number doesn't vary much between houses. Wood doesn't care about your thermostat.

When that shelf is locked into a fully glued case-side dovetail, it can't move out — the joint geometry blocks it. So it tries to move through the joint instead. The glue line runs along the grain, and the shelf's seasonal expansion loads it in Mode II shear: two surfaces trying to slide past each other. Hide glue fails somewhere between 6 and 14 megapascals under that kind of load. A fully glued joint on a 12-inch cherry shelf in a climate that swings 5 or more points of moisture content gets close enough to matter.

Glue only the front 2 to 3 inches and that shear stress drops to about 2.3 megapascals — well inside the safe range for any glue you'd use. The rear of the joint seats the shelf accurately without being asked to resist seasonal movement.

The threshold where this starts to matter: shelves deeper than 10 inches, in primary hardwood (cherry, walnut, white oak), in a climate with a 5-plus-point seasonal moisture swing. Below 10 inches, the movement is small enough that a full glue line stays safe. Secondary wood like poplar has a lower radial movement coefficient, so you have more margin there — but cherry and walnut in a North American climate are right at the line.

The failure mode when you ignore this is audible. A crack, sometimes during a summer humidity spike, sometimes on the swing back to dry. The pop is the glue giving way. Once it lets go, the joint loosens and you're into a repair.

Traditional cabinetmakers glued the front and dry-fitted the rear. They didn't have the numbers. They had enough failed cases to learn the rule the hard way.