[pianotech] Adding weight to Wurly Console action/keys

[Delwin D Fandrich]

See below --

Delwin D Fandrich
Piano Design & Fabrication
6939 Foothill Court SW, Olympia, Washington 98512 USA
Phone  360.515.0119 — Cell  360.388.6525
del at fandrichpiano.com — ddfandrich at gmail.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Dean May
Sent: Saturday, February 25, 2012 8:53 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Adding weight to Wurly Console action/keys

I did a sampling of a half dozen notes down the scale. I put the sustain
pedal down to take the damper springs out of the equation, then I measured
down weights and up weights. I then added a balancing weight to the back of
the key and repeated my measurements. Then I added a weight to the wippen
and measured again. With both weights the down weight came up from low 40s
to upper 60s. Upweights, which is what I was most concerned with came from
below 20 to 40. I figured I could reduce the downweight a little by backing
off hammer spring tension. I also knew I wanted to reduce the damper spring
tension. I was hoping to end up with a downweight of about 50 and upweight
of 30. I was little shy of both targets, but it was still a big improvement.
Attached is spreadsheet with my preliminary measurements.

-- This is one of those typical 90%/10% situations. Assuming the best
possible results are 100%, you get 90% of those results for 10% of the work.
The last 10% of the results takes the other 90% of the work. 



Del, I would love a little more info on adding weight to the damper heads.
How much weight and in what sections? I seriously considered doing that, as
I recall somewhere in the deep recesses of my aging brain it being
discussed. I even dug out Spurlocks notes on redoing dampers looking for
info on adding weights, but he doesn't discuss it. 

-- Someplace back in the dinosaur era I wrote an article for the Journal
about damper systems. Here's the short version: essentially piano dampers
are mass-loaded absorbers. Their efficiency depends on the compliance of the
damping medium--in our case, the felt--and the mass and springiness of the
backup medium--the combined effect of the spring holding the damper against
the string(s) and the combined mass of the mechanism. Bass dampers in a
grand piano work reasonably well because there is a fairly substantial
amount of mass involved; the damper head, wire, underlever, etc. Upright
dampers often do not work well because, even though the spring constant is
fairly high, there is little mass backing up the damping medium. It's an
impedance matching thing. When bass dampers (in particular) ring through it
is usually the higher partials of the wrapped strings that are not being
efficiently damped and that tells us that there is insufficient mass in the
system. The ideal solution is to replace the damper blocks (or barrels) with
something much heavier (like brass). 

While this is fairly easy to do at the factory level it is more difficult
when you're out there looking at that Wurly Console with damper springs set
so hard you can barely push the key down it's a whole other problem. Then
the solution comes in the form of split fishing leads. Whatever size looks
convenient and is available. Roughly speaking, the more mass the merrier.
Size and space probably won't allow you to put too large a lead weight in
there. Once the weights are in place you can go through and take about half
the spring pressure off and still have greatly improved damping. 

ddf