The Key Force 1 directly measures the forces incurred when the damper
underlever is engaged by the key mechanism. As with the down, up, and let-
off forces, the well-controlled plunger moves down - and then up - at constant
speed, measuring the reaction force at the plunger every millisecond. This ulti-
mately results in Damper Down Force, Damper Up Force, Damper Balance
Force and Damper Frictional Force. These values come in both continuous and
average form, as with most of the forces measured by the Key Force 1. These
continuous forces are then plotted as a function of key travel. The four average
values for each note are then plotted across the keyboard. The technician can
then easily see - on a macro level - how the individual notes behave, once the
Just as important as the damper forces produced is the location in the key-
stroke where the damper is engaged - the Damper Engagement Point (DEP).
This point should not only be consistent across the piano, but should also
approximately correspond to the hammer being halfway to the string. One can
"block" half the clearance above a couple of hammers, and let the Key Force 1
quickly tell you what key position that corrresponds to. Knowing this desired
value of "key depression to damper engagement" allows the measured data to
be graphically displayed across the keyboard, against the desired value. De-
pending on the piano's design, the resulting differentials for each note can often
be handled very similar to key leveling data from the Key Force 1. That is, a
spreadsheet shows the data and calculates the required shimming or deshim-
ming. For actions employing a spoon to engage the damper mechanism, more
of an iterative approach must be undertaken. For this reason, Full-Measure
Response has made some progress towards a more interactive routine, when
it comes to damper timing measurements. The result will be some sort of feed-
back and communication between technician and machine, as the spoons are being deformed.
Below are some resulting force-curves from an actual piano key. The first
graph shows the situation on a downstroke, when the damper had been disen-
gaged. The let-off event is the most prominent feature here. The next graph is
of the same "as is" key, but with the damper able to engage normally. The point
where the damper underlever is reached is shown as the Damper Engagement
Point (DEP). A couple of separate tests on this and one other key showed that
the "hammer halfway to string" point corresponded to a key depression of about
4.5 mm. The back of the key was then de-shimmed, in an attempt to get the
damper to engage at this point. The third graph below shows the resulting down-
stroke force curve. The resulting DEP is shown to be 4.37 mm, quite close to
the desired point. With this Damper Product, you receive all of these micro-
graphs, for all notes across the action.
On a macro level, the as-is DEP's are graphed for each note across the keyboard,
and superposed against the desired DEP line. The spreadsheet immediately calcu-
lates and displays the necessary shimming or deshimming required at each note.
Similar to kinetic key leveling analysis, one has both a tabular and a graphical de-
piction of where each key engages the damper mechanism. Such a "macro" graph -
for 14 sample keys of an action - is given in the figure below. The measured "as is"
points - in purple - show that the damper is hitting much too early for most of
these notes. Note that the DEP's are superposed right onto the key leveling (top
and bottom) data. The green squares represent the desired DEP's, approximately
5 mm below the respective "at rest" keys. For a more detailed description of how
the Key Force 1 measures damper forces and timing, please read the article here.