Leveling a plate? Del? Ron? Anybody?

[Delwin D Fandrich]

harvey wrote:

> It makes sense to me. Now that you've had your coffee, another question.
> Assume as constants that vertical pin material is harder than normal hitch
> pins; that there is less string trauma from bends, and even that there is
> better energy transfer from string to bridge (less clamping effect), what
> about the mechanical ramifications of a retro-fit? Off-the-top thoughts:
>
> Weakened surfaces from removing(?) existing hitch pins;

We may or may not remove the originals.  If they are where we want them and if
they are drilled straight you can just pop out the originals, re-drill and drive
in the new pins of whatever design you choose.  Occasionally we will relocate the
pins in which case we will simply shear off the originals, fill with epoxy putty
and spray over.  The original hitch pin panel will be weakened by whatever amount
of iron is removed when the holes are enlarged as they invariably are.  You have
to be the judge as to whether the original plate has enough structural integrity
to take this.  Most do, a few do not.

Where we use them most often is in the bass section where this is most always a
moot issue.  The bass hitch pin panel or riser is generally overbuilt for its task
and can easily handle the slight added stress.



> ...considerations of original plate thickness in desired mounting location.
> Again, you have to be the judge of this.  Most hitch pin panels have adequate
> thickness and strength to easly handle the change in stress.



> I'm trying to make an analogy with a straight nail and one that is
> toe-nailed. It isn't working on face value, since there's no potential at
> the -top- of either nail. So, I'm curious about what sort of forces exist
> at the -bottom- of a straight pin that has xx pounds of one-way potential
> at the -top- of the same pin. Is there a possibility of tear-out if the
> plate was not originally cast for this use?

What would be the difference between one that was cast for the purpose and one
that was retrofitted?  I have so far failed to see the difference.  As long as the
panel has adequate thickness I don't worry about it.

The only cases in which either a technician or a manufacturer has gotten into
trouble using vertical hitches (that I am aware of) is when they have been grossly
mis-used.  That is, when the string has been placed much to far up on the hitch to
accommodate an over-height bridge or a plate that was mounted to low.  They are
not intended to be used to cover for sloppy work, but are often called on for this
purpose.  I've seen some pianos that had the strings as much as 10.0 to 12.0 mm
off the plate surface.  One small grand I examined had them 15 mm above the
plate.  (And the string bearing against the bridge was still way excessive.)
Quite a bit of stress there -- I'm still surprised the plate hadn't snapped.  My
rule of thumb is that the string should not be any higher on the pin than it was
on the bearing bar that used to be there.  This generally places the string no
higher than 6.0 mm from the plate surface and usually a bit lower -- around 4.0 to
5.0 mm is generally about right..

Del