Est. 1998 — 27 years of woodworking knowledge
The Dovetail Illusion
You cut a perfect through-dovetail joint with equal tails and pins.
When assembled, the joint slides together smoothly for the first half, then binds tightly even though no glue is present.
What’s the geometric reason this can happen?
I'd say increased friction due to increasing amount of contact the further the parts are driven together. I don't think that's geometry, though. Friction is more clearly evident with a longer sliding dovetail.
@Dave Bair,
Agree, but I think it is a geometry effect that creates the friction. The friction isn’t the cause — it’s the symptom. If the tails and pins were shaped with perfectly parallel walls (a sliding dovetail with no taper), the joint would slide smoothly with nearly consistent friction along its entire travel. But nothing in the world is perfectly shaped--except Taylor Swift.
It’s fundamentally a geometry/wedging phenomenon.
A dovetail’s angled walls form a tapered, self-locking shape. As the joint goes deeper:
the angled faces overlap more,
the side pressure increases,
the mating parts push outward against each other,
which creates normal force,
and normal force × coefficient of friction = higher friction.
So the binding occurs because the geometry increases the normal force, and that makes friction ramp up sharply.