[CAUT] downweight vs. balance weight/capstan move

[Jon Page]

Bob,
I favor a SW down the middle of the medium zone but a performance 
piano could be higher.
That 2g drop between #28 and 29 shows that the weight needs 
attention. I would expect a
jump between 20 & 21 not 28-9. Is #64 really 12.8??

You could trim a gram off just about every note and still be in the 
high weight zone.
That in itself will drop the TW (touchweight) ~5g. Then the FW could 
be adjusted
to target BW  (-1g FW = +1g BW).  If that's not possible, look into 
assist springs
and drop some FW to lower the overall inertia.

You didn't say what the KR is.  I find that a .52 is a good target.
A way that I have had good results with selecting a capstan location
and angle is to mark the wippen cushion/magic line intersection.
With the hammer blocked at half-blow, draw a line perpendicular to the cushion
(or parallel to the wippen post) through the 'mark' onto the key.  This is the
position and angle for the capstan.   This places the capstan perpendicular
to the wippen at half-blow and has it moving through equal angles between
rest and full dip through half-blow.

My criteria for optimum capstan location is regulation. I want the 
jack to end up in close proximity
to the knuckle at full dip.  If the jack is pushed so far as to bury 
into the stop felt, the capstan can
locate more forwards. Alternatives would be to the regulation (which 
won't affect TW)
decrease dip / increase blow.  For any given set of parameters: bore, 
dip, hammer blow,
knuckle radius; there is an optimum intersection (KR) between the 
capstan and wippen cushion to minimize/optimize jack travel.   If it 
doesn't travel far enough, you risk bobbling. If it travels too far 
it is a waste of energy.

My point of view is that the key has to move the wippen through a 
specific distance for optimum
action performance. The greater the KR, the greater the wippen travel 
(given the same key dip)
and consequently higher TW numbers. (Not getting into stack location)

Getting a smooth SW curve is important. From a shear regulating 
standpoint it causes the rep
springs to be more consistent.  For instance, #28(12.7g) rep spring 
is going to have to be stronger than #29 (10.7g)rep spring because of 
the difference in their SW's.  This causes more resistance at let off 
on 28 than 29.  Voicing is reduced because you are only dealing with 
a resiliency issue and not a weight differential issue.  Then there's 
that little thing about inertia...

Because of all the minor geometry anomalies from note to note a 
smooth SW and a smooth FW will not produce a smooth BW.  To get a 
smooth SW/FW and an even BW you must incorporate wippen assist 
springs.  Otherwise a smooth SW and even BW produces a jagged FW.

I don't think this answered your question specifically but your low 
SBR will support a high SW.
 From there it's a balancing act between leverage and regulation.

Jon Page
-- 

Regards,

Jon Page