On 7/20/2012 1:04 PM, dadiOH wrote:
dpb wrote:

That they tend to come out of the rails and not the stiles is owing to
that the in the stile they're along/parallel to the grain; in the rail
it's almost entirely end grain. That is much less strong.


Excuse me? Are you saying that a dowel glued into the rail is less strong?
If so, I beg to differ.

You can differ all you want but it doesn't change the fact (nor the
orientation of the grain)

Of course it is (weaker in the cross direction, that is)...it doesn't
have nearly the amount of long grain to bond against in solid wood. (As
noted below, in quality plywood or composites there isn't much if any
difference).

Believe it or not, they study this stuff...

Eckelman, C.A. 1969. Engineering concepts of single-pin dowel joint
design. Forest Prod. J. 19(12):52-60.

--1971. Bending strength and moment-rotation characteristics of two-pin
moment-resisting dowel joints. Forest Prod. J. 21(3):35-39.

--1979. Withdrawal strength of dowel joints: effect of shear strength.
Forest Prod. J. 29(1):48-52.

Are two of which I've known for quite some time--I couldn't find them
online in a quick search. They do this for the furniture manufacturers,
primarily, w/ certainly applications to stuff like these doors, etc.,
etc, etc., ...

I suspect there's also supporting data in the US FPL's landmark tome the
Handbook but it's humongeous and I didn't try to search just now...

Title: .Wood Handbook, Wood as an Engineering Material (29 Chapters)
Publication: Forest Products Laboratory. Wood handbook - Wood as an
engineering material. General Technical Report FPL-GTR-190. Madison,
WI: U.S. Department of Agriculture, Forest Service, Forest Products
Laboratory: 508 p. 2010

This kind of research is where the data comes from that "joint strength
increases with clamping pressure", too....

Interestingly enough, and as one might expect, when the substrate is
furniture-grade plywood or many of the other composites, then one
doesn't find the directional bias. This is pretty easy to digest since
there is really no preferential grain direction in those materials.

But, all that aside, they're "strong enough" when sound; the point here
is that because of the (primarily) cross-grain construction they're the
ones that do tend to fail first (as attested to by the observation that
they're the ones he can get out).

Generally the failure mechanism is one in which the dowel typically
either shrinks or at least becomes oval. The comparative effect is less
when the dowel and the surrounding hole are in the same grain direction
as the transverse movement of wood is almost all in the across-grain
mode. When the dowel is perpendicular to the grain the two sides
directly abutting end grain essentially see no wood movement.

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