Sustain pedal lift ratio

[Ron Overs]

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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