Reaming Agraffes

[ed440 at mindspring.com]

Frank-
Very good comments!  They will mostly apply to pianos of recent manufacture.  Older pianos will generally have the flat to flat agraffe to plate contact.
The newer agraffes I've worked with have an angled bottom surface which allows the brass to compress at the outer edge as you described.
Wouldn't it be nice if the piano supply houses (anybody on line?) would supply a counterbore that cut an angled surface instead of a flat surface?
Ed Sutton

----->Frank wrote:
>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
>
>