Backchecking problem

[Robin Eugene Hufford]

Thomas D. Seay, III wrote:
> 
> Dear list,
> 
> I am stumped with the backchecks on this piano. The piano is an early 80s
> S&S L with new Premium blue hammers on Renner shanks & flanges and
> re-leathered original backchecks. I have CLOSELY regulated key height, dip,
> let-off and drop, spring tension, and all the other usual suspects. The
> problem is that the hammers absolutely refuse to check when the note is
> played at the level of forte or less. They just bounce between the
> backcheck and the string. The angle of the backchecks is good and they
> check high enough, but I just can't seem to get them to work in the piano.
> The problem is particularly bad in the bass and tenor, where the hammers
> are larger.
> 
> The problem may be in the balancier. When I push the balanciers down, there
> seems to be much more spring resistance than normal although the hammer
> rise is not particularly fast. The original wippens have been rebuilt and
> repinned, so I'm pretty sure that it is a not pinning problem. The slots
> are clean and the springs have been cleaned and polished.
> 
> I'm pretty much at my wit's end and if I don't get this resolved soon, I'm
> going to have to take a hostage. Any and all help will be gratefully
> appreciated.
> 
> Many thanks.
> 
> Tom
> 
> Tom Seay
> Piano Tech Office
> School of Music
> The University of Texas at Austin
> t.seay@mail.utexas.edu
Tom,
     It is likely that the pining of the repetition flange is too loose,
not too tight as has been suggested, even though I am sure such
scenarios do occur, and the resulting too great repetition spring
tension is not allowing the check to grab and hold onto the tail.
      The Renner hammer and shank are somewhat heavier, even when well
worked, than original parts.  As the hammer rebounds from the string it
is decelerated by three principal components - friction in the pining of
the hammershank flange, the repetition flange and the spring tension.
The hammerflange is of lesser concern than the rep flange.  As the
repetition flange friction becomes less, whether due to wear, poor
design or whatever, the repetition springs must be increased
substantially to compensate for the loss of friction in the rep pining.
This then produces as situation where, other factors being correct, a
level will be found where the checking will occur as you have
described.      This is seen occasionally on older grands where the
pining is loose.  A good visual demonstration of a rep spring being too
loose is to gently move the key and hammer to the beginning of the
let-off sequence and then very slowly move through let-off  and then
stop the motion of the key and rise of the wippen.    While this is
happening watch the drop of the hammer. If pining is too loose, as I
suspect, then the hammer will be seen to fall freely, loosely and
rapidly as it  passes through the drop level and will continue sometimes
as much as a quarter of and inch or more as the spring tension works to
decelerate the hammer assembly and return it to the drop level.  There
is a characteristic, quick kind of motion here that is easy to perceive
and distinguish from a correctly pined flange which does not descend as
far due to the effects of the friction on the center pin. 
    As you know poor pining is a very common problem on the notoriously
unstable teflon bushed whippens of pianos of that period and if this
piano retains the teflon, which your post does not indicate, then that
may be the source of the problem.  Or, if cloth bushings are in place,
excessive drying, poor pining from the factory, wear, etc. etc. may
account for this condition.   
    I would be curious to know what you find the prolem to be.  
Robin Hufford, RPT
Fort Worth, Texas 
hufford1@airmail.net