Reaming Agraffes

[Frank Emerson]

It looks like this thread has just about played out, but there is one
consideration that has not been addressed, and should be taken into
account.  I take no exception to the proposed solutions, but feel that I
should chime in from a manufacturer/designer's perspective.

Most modern agraffes are designed with a rounded bead around the bottom
edge of its base.  It's function is to minimize the surface area of contact
between the agraffe and plate, and therefore, minimizing the amount of
compression of brass required to turn the agraffe into alignment with the
string(s), which could be almost a half turn beyond first contact of the
agraffe with the plate.  In manufacturing, the height of the agraffe is
controlled by the depth of the counterbore in the plate.  Typically, this
is done with CNC milling machinery.  These machines have very precise
capabilities, but if the plate is not supported adequately from the bottom,
and/or the machine cycle is run too fast, the implied accuracy of the
machine can be significantly compromised.  It is amazing to observe how
much a cast iron plate can flex under the impact of these machine cycles!

The point is this:  Ideally, material should be removed from the plate
counterbore, not the agraffe.  Removing a barely visible amount of material
from the agraffe can increase the contact surface ten-fold.  The more
material you remove from the bead on the base of the agraffe, the more you
increase the contact surface, the more compression of brass is required,
and the greater the risk of breaking, fracturing, or weakening of the
brass, while turning it into alignment with the string.  

By removing material from the agraffe rather than from the plate, you may
be recreating the same problem that you are endeavoring to repair, an
agraffe that is weakened and will eventually break for another technician
to repair yet again.

Frank Emerson
pianoguru at earthlink.net


> [Original Message]
> From: Joseph Garrett <joegarrett at earthlink.net>
> To: pianotech <pianotech at ptg.org>
> Date: 11/2/2006 2:37:46 AM
> Subject: Re: Reaming Agraffes
>
> Thanks for the tip. I actually tried something akin to this. I drilled a
> 1/4 inch hole in a packing block I got from the bottom panel of a Kawai
> upright, attached some sandpaper, and turned the agraffe around many times
> while applying pressure. I didn't see any brass flecks coming off, so I
> assumed it wasn't working.
> Guess I need to have a bit more patience!
> Dave,
> You have the right idea, but you need to use cloth backed abrasive instead
> of sandpaper. It'll do the job quicker and smoother.
> Regards,
>
>
> Joseph Garrett, R.P.T.
> Captain, Tool Police
> Squares R I
>
>
>