[pianotech] dowels and glue joints

[Douglas Gregg]

The dimensional stability of a dowel is very good with the grain. Most
expansion and contraction of wood shows up in the width (across the
grain). Think- wood floors that open and close between boards side by
side but not at the end joints. That being the case, it is very
unlikely that a glued dowel will force a joint apart. In fact that is
why they are used. If a joint comes apart it may more likely be due to
glue failure and/or warped pieces under great tension needed to close
a re-glued joint.

BTW-You may have noticed that old dowels are not always round. This is
because of shrinkage across the grain that makes the dowels oval. They
shrink more in one direction than the other. But they don't shrink
much at all lengthwise.

I sometimes will bury a screw for added strength across a joint that
is under great stress,  and countersink it and plug it with matching
wood. If you choose to use a metal rod, be sure to use epoxy rather
than wood glue.

Doug Gregg
Classic Piano Doc
Southold, NY

Message: 1
Date: Thu, 21 Jun 2012 09:32:26 -0700
From: "Larry Fisher RPT" <larry_fisher at pdxtuner.com>
To: <pianotech at ptg.org>
Subject: [pianotech] dowels and glue joints
Message-ID: <33CF707A5CC44D08B576C9DA45C846BB at LarryPC>
Content-Type: text/plain; charset="utf-8"

I?ve always enjoyed doweling a glue joint when possible.  Even an
eighth inch dowel across the break can improve the bond if only from a
mechanical aspect.  Recently however, this young man I mentioned
earlier reported seeing a glue joint fail from what he considered to
be the tension created by the cross grained conflicting expansion and
contraction  ..........  or at least that?s the way I understood his
explanation.  The object of discussion was a grand leg whose
laminations were separating.  I?d welcome any additional thoughts or
comments on this.

Isaac, I sure do like your idea of a hose clamp and some rubber hose
to clamp a round or uneven surface  .......  French leg comes to mind.

I?ll most likely continue to use dowels across the break.

One recent application involved a Lowrey console in a school where
moving the piano across an expansion joint made both front legs very
loose.  The legs themselves didn?t break but the keybed did.  After
clamping the glue stuffed break I doweled the break from just under
the keyslip with half inch dowel and touched up the resulting ?dot? in
the finish.  The customer was happy with the results and I got paid
............  and that my friends is the bottom line!!
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