Doweled and Fully Fit Pinblocks

[David G. Hughes, RPT]

Everyone,

    I've been following the discussions on the M&H BB pinblock.
    It think it might be constructive to differentiate between a doweled
pinblock and a fully fit pinblock. For starters, all doweled pinblocks are
fully fit, but not all fully fit pinblocks are doweled. From the
manufacturer's standpoint, his fully fit pinblock is almost always doweled.
    This begs the question: why are factory fully fit pinblocks doweled to
the stretcher? Certainly in the case of Steinway (and this reasoning is
applicable to other brands), the pinblock and stretcher assembly are
glued together in a press long before the case into which it will be
installed is present. As we know, when gluing two pieces of wood together
the glue acts as an excellent lubricant when the moment comes to clamp up,
and the members of the assembly slide wherever they wish. Steinway's five 
blind
dowels keep their pinblock/stretcher assembly in alignment when the two
components are buttered with glue and forced together in the press.
    I've done the math, and the surface area of these five dowels adds a 
mere
7% of additional surface area to the joint. For my money, this constitutes
negligible additional strength. Thus the dowels are present for
ease/accuracy of manufacture. With both the pinblock edge and the back of
the stretcher well surfaced on a jointer planer and dry-fit air tight, that
1.5" tall by 52" long glue joint is quite sufficient to bond those two
wooden members for 100 years or more. We all know the veneer on the back of 
the stretcher sometimes comes loose from the core lumber before the 
pinblock/stretcher joint fails. Notwithstanding, if the piano is designed 
and built
properly there is little-to-no stress on this joint.
    Now let's focus on the rebuilding end of it. We as a trade tend to omit
the blind dowels for two reasons. First, when we clamp and glue the pinblock
into the case, the stretcher is already present. It is immobile vertically
and laterally. With the new
pinblock fully fit to the insides of the outer rim at the bass and treble
ends and ready to mate up to the back of the stretcher, there can be no
lateral or fore/aft sliding
of the pinblock during glue up. It's captured within the case. Therefore 
dowels would serve no mechanical
expedient.
    Assuming the rebuilder installs the plate and new pinblock
simultaneously, the plate serves as the final vertical tweaker of the
pinblock elevation in the middle of the scale. While the glue is still wet,
all the plate webbing
screws are installed to cinch the block up to the underside of the plate in
the center,
then the stretcher is clamped home to the edge of the pinblock
reestablishing the factory-style fully fit pinblock joint. If dowels are to 
be
installed subsequently, the plate must then be removed once the glue has
cured to "toe" the dowels into the stretcher through the top layer of the
pinblock at a shallow angle (new Mason & Hamlin pianos are reinforced in
this exact manner). Few rebuilders wish to remove the plate once it has been
finally installed. Time is money, and we all lose it quite nicely, thank
you.
    Thus rebuilders by and large churn out fully fit but not doweled
pinblocks (and yes, some factory pianos we all have encountered have sported
this type of joint, too). Personally this un-doweled version is my
preference. I am certainly aware there are other meritorious ways to acheive 
this joint.
To each his own. I do however endorse the
three-sided (bass end, stretcher, treble end) fully fit pinblock in all 
brands of piano. For me, omitting this
step is akin to ignoring a continuous inner rim/outer rim separation or a
loose crossblock within the case. I want to do everything possible to make
the piano a wooden fortress.

    Dave Hughes, RPT
    Baltimore Chapter