"Chris Friesen" wrote
> In the specific context of panel glue-ups, (or even face frame to
> cabinet joints) do you think that biscuits are more than alignment
tools?
Depends ... not "one size fits all" situations.
>
> I'm no expert, but from everything I've read and researched, glue alone
> should be plenty strong in both of those cases.
No question about that ... it is most often _all_ you need ... if that is
all you're after.
> For miter joints, edge-to-face, end-to-face, end-to-end, etc. I fully
> agree that biscuits can add significant strength as compared to glue
alone.
Do the following with regard to edge to edge panel gluing:
1. Lay out your panel boards side by side, with no biscuits and no glue on
the edges.
Now try and pick up all boards at the same time and notice, other than
friction, and for all practical purposes, there is no "joint strength"
whatsoever.
2. Lay out your panel boards side by side, with biscuits, but no glue on
either the biscuits or the board edges.
Now try and pick up all boards at the same time and notice that adding the
friction attributable to the glueless biscuits in their slots has added a
small, but measurable amount of "joint strength" over 1 above,
particularly
in shear strength, which is one of the ideal components in a joint of this
type.
3. Lay out your panel boards side by side, this time with biscuits
properly
glued in, but no glue on the board edges.
Now try and pick up all boards at the same time and notice, after
sufficient
clamping/drying, a relatively significant amount of increase in "joint
strength" over 1 and 2 above.
4. Lay out your panel boards side by side, with biscuits properly glued
in,
and with glue properly applied to the edges. After sufficient
clamping/drying, measure the joint strength.
Now tell me, with a straight face and clear conscience, that steps 2 and 3
added NOTHING in strength whatsoever to the final "joint strength" in 4!
:)
Granted, you may not need it, but it won't hurt and it just may be there
when you do (and easy/cheap insurance for those who prefer a belt and
suspenders approach for posterities sake).
That said, there are other reasons for adding biscuits to a panel glue-up,
other than "alignment" and the arguable possibility of added "joint
strength":
Joint "creep" .. which, IME, is particularly noticeable in wood cut off
the
log in a manner that much of the dimensional instability is reflected in
movement in thickness (as you often experience in quarter sawn woods),
instead of across the grain width.
IME, there is a noticeable decrease, over time, in the effects of this
phenomena when using biscuits in panel glue-ups.
YMMV ...
--
www.e-woodshop.net
Last update: 5/14/08
KarlC@[EMAIL PROTECTED]
(the obvious)
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