hammer travel / burning angle

[John Delacour]

At 12:09 pm -0400 23/9/06, KeyKat88 at aol.com wrote:

>What is meant by the burning angle for hammers. The bore angle? 
>Maybe I know this concept by a different name.

I hope so.  Goodness knows where the term "burning angle" originated. 
On this list, almost certainly!

The proper term is "cast", as in "casting tongs", the tool used by 
some people to heat upright shanks to enable them to be twisted, and 
"casting lamp" as used most commonly on grands.

The hammer head is cast (or not) in two planes : back and forth, and 
side to side.  Provided the hammers are properly bored for the piano 
(a big proviso!), the fore and aft casting is set by the bore and it 
ought not to be necessary to change this angle.  As to left/right 
casting, this will also need no adjustment provided the hammer-heads 
have been glued on at the proper angle and provided the shanks have 
been perfectly "travelled" beforehand.

In practice, either because the travelling has not been perfect or 
because the head has been glued on at the wrong angle, adjustments 
need to be done at the end of the job.  Major errors must be 
corrected by removing the hammer-head and re-gluing at the proper 
angle, but fine adjustments can be made by heating the shank with the 
casting lamp and twisting the shank to correct the angle of the 
hammer head, after the correction has been made to the hammer travel. 
A skilled hammer installer will make very little use of the lamp.

As has been mentioned, certain pianos are designed in such a way that 
some of the hammer heads are at an angle of a few degrees to the 
vertical, and this should be taken into account at the gluing stage 
and not left to be corrected with the lamp.  Some Steinway grands, 
for example have the bass hammers leaning to the right and the tenor 
leaning to the left.

"Travelling" is a separate operation altogether, and there should be 
no confusion between travelling and casting.  The hammer shanks must 
travel in an arc that is at a right angle to the hammer rail.  Owing 
to slight irregularities in machining, bushing etc. this will not 
necessarily be the case, and the errors need to be corrected by 
sticking thin paper strips under one side of the hammer flange until 
the shank moves in a vertical arc.  This should be done before the 
heads are glued on.

Another, and the first, important thing to check, is the rest 
position of the keyboard, and careful adjustments must be made to the 
thickness of the stop block (usually to the left of the key-frame) so 
that when the hammer-shanks in the mid-treble are properly aligned 
with the levers (wippens) and the head is perfectly vertical, the 
hammer strikes the trichord centrally (or slightly to the left). 
This work needs to be done with pattern hammers temporarily 
installed, perfectly travelled and aligned.  If it is omitted, the 
whole job will be a compromise.

JD