[BULK] Re: Sustain pedal lift ratio

[Alan McCoy]

Great post Ron!! It came at just the right time as I knew I was going to be
troubleshooting a very stiff sustain pedal.
 
I was just out today checking it out. It's on an S&S M. I measured the
system and the numbers are: (inches)
 
A/B = 4"/3.25" = 1.23
C/D = 10.3"/7.5" = 1.37
E/F = 2.25"/3" = .75
Lift ratio = 1.26 to 1
 
What I found out later was that the piano had been in storage for awhile and
for some reason the trapwork levers had been removed from the piano while it
was being stored. The owner, in a moment of "clean out the garage madness,"
inadvertently tossed out the levers. I'm guessing that someone bought new
levers and pivot blocks from S&S and installed them. When he told me about
his tossing the levers, things began to click into place - unfinished levers
and pivot blocks, writings on the levers for such things as "coil spring"
next to the place where the coil spring goes, etc. 
 
My plan for this is first to replace the old-style
pitman-through-the-bushed-hole with the new style pitman with a 1" hole
through the keybed for clearance. This will bring the tray leverage a bit
closer to 1:1 (but I'm guessing it will still be 0.9:1 at best). Then the
pivot brackets will need to be moved closer (4" or more if it's possible) to
the pitman so the trap lever ratio will be more like 6.3"/3.5" = 1.8. Still,
even with these changes this system will be more like 2:1. There's
presumably nothing to do with the pedals as they are normal. 
 
It'll be better, but still not great. I'll measure some other S&S Ms that I
have at my school for some comparisons.
 
Any suggestions?
 
Thanks so much for this information.
 
Alan
 
--Alan McCoy, RPT
Inland Northwest Chapter
Spokane, WA
ahm at webband.com 

 

  _____  

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Overs
Sent: Friday, November 10, 2006 11:04 PM
To: Pianotech List
Subject: [BULK] Re: Sustain pedal lift ratio
Importance: Low


Hi all,

At 10:48 AM +0100 10/11/06, RicB wrote:


... I'd like to hear more about how you go about designing a change in the
lever systems.  I remember my brother Joe doing this to accommodate
pianodisk systems... tho I dont think he was concerned directly with the
lifting ratio... more a matter of making everything fit.

Still.. this might be a nice addition to ones technical toolbox as it
were....


At 5:01 AM -0600 10/11/06, Conrad Hoffsommer wrote:


I second this. The difference in feel, usually expressed as "heavy"/"light",
has been noted more lately by both students and faculty.


The lift ratio and the resistance of the pedal system are two separate
issues, regarding the performance of the sustain pedal. Most manufacturers
fit a return spring to the damper lift tray, the sustain lever directly
under the keybed, or both. The return spring on the damper lift tray can
create problems over the longer term, since its not usually possible to
position the spring directly over the push rod. When the return spring is
offset from the push rod, the damper lift tray can develop a compression-set
warp over a number of decades. This is a long term problem which won't
usually occur while those who built the piano are alive. Eventually, once
the builders are lying quietly in a box on a hillside somewhere, some repair
tech in a workshop might be found whining about another case of poor design
staring them in the face, as they deal with a warped damper lift tray.

I prefer not to fit a return spring on the damper lift tray for the reasons
above mentioned. For those damper systems where the push rod is located via
a bushed guide hole in the keybed, it is best to convert these by drilling a
larger clearance hole in the keybed and fitting a push rod with a guide pin
in each end. This will be quieter, creating less friction and noise. Its a
good policy to make and fit a new pin-guided push rod when rebuilding pianos
with the older style bushed push rod.

As mentioned in my previous post, most pianists seem to prefer a
pedal/damper lift ratio of between 2.5 to 3.25 to 1. When making an
adjustment to the ratio, I prefer to set it between 2.5 to 3.0. But for some
pedal systems 3.25 is about as high a ratio as can be achieved using a
single lever under the keybed. So, in these cases I'll go as low as 3.25
because the double lever design, as used in the Grotrian 275 conversion
image I posted yesterday, is a whole lot more trouble.

I check an existing damper lift ratio by measuring the damper-head lift, and
measuring the damper pedal travel from the end of the lost motion to full
lift. The pedal travel is divided by the damper-head lift to arrive at an
overall ratio.

If I need to revise the ratio, the formula for calculating the lever lengths
is similar to the formula I use for calculating action ratios. Each pair of
lever lengths is divided one into the other, with the three results being
multiplied together to arrive at an overall ratio.

The three lever lengths are the pedal pair, the lever under the keybed pair,
and the damper tray pair. Here's a graphic to show the various lever lengths
A - F.




The pedal/damper lift ratio is calculated using the following formula.

(A/B) X (C/D) X (E/F)

For many damper systems, the push rod will come through the keybed to
contact the damper tray almost directly under the damper wire flange. In
these instances you can disregard the lever lengths F and E, giving them a
value of 1. There will be some small variation in the actual ratio due to
variations in the lever angles from piano to piano. However, the variation
is too small to worry about in practice with respect to the ratio, but the
lever angles are critical with regard to friction.

If the push rod is fitted with guide pins the angle of the push rod, with
respect to the damper tray and damper lever, won't be of much consequence,
since it will contribute very little friction. The damper lever under the
keybed is a different matter. I prefer to set this lever so that it is
horizontal at half damper lift. This arrangement will minimise friction
between the lever and the lyre push rod. For our own 225 piano, we machine
away the lower-half of the damper lever thickness where it meets the
push-rod capstan, and lengthen the lyre push-rod so that the lever is
horizontal at half damper lift. This results in less friction and less
likelihood of squeaks developing between the lyre push-rod capstan and the
lever bearing-felt.

I hope you have found the above mini-doc to be useful, since this is the
first time I've written-up the procedure onto something more substantial
than a piece of scrap of paper around the workshop. However, its been good
for me to document the procedure.

For those of you who would like to know how I produced the graphic and
imported it into the Eudora programme, here is the procedure.

1) Draw the graphic using my old 2D CAD programme.
2) Capture a screen image of the drawing and save it to the desktop as a
TIFF file.
3) Open the TIFF file in Photoshop, resample, reduce in size and save as a
jpg file.
4) Drag the jpg file into the Eudora email document.

Ron O.
-- 
OVERS PIANOS - SYDNEY
   Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:ron at overspianos.com.au
_______________________

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