Broken tap

[A440A@AOL.COM]

  ANRPiano@AOL.COM writes:
>referred to me by a very good technician who had the miss 
>fortune of breaking a tap while retapping agraffe threads. 

        Most broken taps I have seen come from the operator not lubricating 
or not backing them out as they progress through the threads.  The residue 
can gall, creating a bind that is all out of proportion to the amount of 
material being removed. However, to break a tap while CLEANING threads is 
indicative of either a faulty tool, the wrong size being used or the operator 
being totally insensitive.  If anybody else has additional causes, I am all 
ears. 


>I attempted to drill the tap out.  My titanium bits did little.  Though
>the 
>grinding bits I used to flatten out the top seemed effective in removing
>material.  Is there a solution here?
>The customer does not have enough money for rebuilding the piano (which
>it could use) so removing the plate and coming in from the bottom is out.
 
    There are several things to try.  You will need a carbide bit to have any 
success in drilling into that tap,  it will be hardened steel.   Using a 
diamond tip something, put a centerpunch hole in the center of the tap, and 
drill a 3/32" hole about 1/8" deep.  This is not clumsy stuff here, you will 
need to be very patient and careful. 
       	Put something,(like the stem from an old 3/32" bit) in this hole and 
begin to gently hammer it .  This will knock some freedom into the fit 
between the tap and the plate.  you may then be able to begin working the tap 
back and forth until it is sufficiently free to make a full revolution.  On 
many pianos, you will have access to the bottom of the agraffe hole.  If so, 
cut a steel rod, (or another broken off drill bit of the correct diameter),  
short enough to allow you to swing something against it from underneath,  
this will also loosen the broken off tap. 
 >My last idea (which I don't care for) is to drill a new agraffe hole infront
>of the old.  There is plenty of room in the plate.  Will this cause any
>undue  weakening in the plate, and how badly will the tone on the now 1/2 - 
3/4
>inch  shorter be affected?

     I must respectfully suggest that this would be ruinous.  Get a micro 
torch and anneal the tap.  This can be done without overly heating the rest 
of the piano, but you will want to do it fast. You could place a collar of 
sheet metal around the working diameter of the agraffe base, and perhaps 
avoid ruining a lot of the paint job. once softened, at least near the top, 
you may be able to use an EZ-out or similar small reverse threaded tool to 
back it out.  

    I am rather cavaliere about breaking off my drill bits when I need a 
diameter.  In comparison to the time involved in finding a substitute, they 
are cheap.  It may not be practical to use drill bits as diameter stock for 
those that are a long way from the hardware store, but if saves me a lot of 
expense.  It also keeps my drill index in fine, sharp condition. 
Regards,
Ed Foote