>>a Bechstein grand piano model B (203 cm) dating 1988 (one of the last with
ivory keys). I have a question about proper bedding procedure for this piano.
The main concern is about bedding it with keys and action installed or
without them using the paper method under the bolts.
In the first case should I tighten the cheeks screws? And in what order
should I regulate the bolts?
Should the keyframe of this piano be considered rigid or flexible?<<
Greetings,
All key frames are flexible. The best bedding would require you to remove
the action stack and with keys on the frame, in the piano, make sure you have
full contact under the front and rear rails(think sandpaper on the bottom of
the keyframe, leave the keybed alone!). Turn your bolts up until there is a
very clear knock when the glide bolts are tapped.
Set the action stack back on the action (no screws in,yet) and slide it
all into the piano. There should be no taps heard on the balance rail. This
tells you that you have compressed the action enough to make firm contact front
and back, and that the balance rail bolts are touching. How firmly do they
need to touch? There is some controversy about that. I like to know that the
front and back rails are bearing the majority of the weight of the action, and
the glide bolts require some effort to lift off the keybed.
If you can grab the top of the glide bolt,and with thumb and forefinger
only, lift it enough to hear a knock, you may want to add just the smallest
amount of bearing. Or leave it as is, depends on you need for insurance. I like
to start with the glide bolt nearest the middle, turning it down to stop the
knocking, then work my way outward. I listen to all previously set bolts after
changing any new one. You will eventually learn to add slightly more
pressure on the first bolt set, and slightly less on all those that follow, until you
reach the ends and just barely need to touch them down.
A more rigid keyframe is less forgiving of excessive balance rail
pressure, you can lift the front rail off the keybed with slightly too much pressure.
A more flexible frame has more tolerance, and will even allow you to move key
height up and down without upsetting the front rail contact.
After you have this done, use a flashlight and make SURE that every single
action frame foot is seated on the wooden cleats on the keyframe. If there is
a gap, shim it. You don't want a mismatch being held in a "spung" state when
the action screws tighten everything together. You want the keyframe to be
bedded in a very stable manner, and you don't want a bent or torqued action
frame to upset it.
>>The 2 procedures give very different results, expecially in the middle
registers. What bothers me a lot is checking key height after bedding. It should
be 63 mm (that's what Bechstein told me), and this is correct on the left and
right side, but if I do the bedding with action and keys installed I obtain a
much lower key height in correspondance of the 3 middle bolts. Could the
keyframe have bended in the balance rail over time (in case it is a rigid kind)?<<
Your keys may have lost their level and the bedding doesn't have anything
to do with it, OR, somebody could have set the key height with a lot more
pressure on the balance rail.
>>Is a bedding procedure based exclusively on "sound quality" be imagined?<<
Some have said so. I don't find it makes a discernable difference as long
as the bedding is within normal bounds.
>>How does a correct key height influence sound quality and pianist feeling?<<
It can directly influence the intersection of the arcs of the capstan and
whippen, which may change your rate of acceleration as the key goes through
the range of motion. This will be pretty slight, but in an action with other
marginal tolerances, it can be a problem.
I don't think it directly influences the sound.
regards,
Ed Foote RPT
http://www.uk-piano.org/edfoote/index.html
www.uk-piano.org/edfoote/well_tempered_piano.html
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