"Mastertouch" action regulation

[Greg Graham]

I was asked to regulate a 1917 Lafargue upright with
the relatively rare "Staib-Abendschein Co.
Mastertouch" action.  This is the one with the wooden
arm attached to the hammer butt that grabs the
hammer-head shaped jack for "checking" instead of a
normal backcheck and catcher.  It's the version with a
conventional letoff rail, and the flat checking spring
rather than the coil.  

See: 
http://www.ptgcolumbus.org/files/page_pics_Staib.html

Jack Wyatt and Dave Peake have written about this
action in the archives, and recently Tom Harr of
ptgcolumbus.org posted the nice photos in the link
above and the Columbus newsletter, but I didn't see
any mention of how to regulate the checking.  (Yes, I
know you turn the regulating button screw, but which
way for what result, and what it the target
distance?).  

It appears to want to check very close, perhaps 3/8ths
inch.  I say "it wants to", because I found I had
little control over checking, other than on/off.  It
either jambed up before the hammer hit the string,
checked wherever it wanted, or didn't check at all. 
Is it that much of a hair trigger?  I must be missing
something.

Anyone a "Mastertouch" expert?  

As I found the piano, there was lots of
double-striking.  Excessive blow, insufficient key
dip, lost motion, wide letoff.  (Letoff regulation was
a breeze with no backchecks to get in the way). 
Mercifully, it had none of the check flange
self-destruction others have found.

When setting up a few test notes, I cranked up the
capstan to get some aftertouch.  In a normal action, I
would expect the checking to decrease and perhaps push
the hammer to the string as the wippen moves higher. 
The "Mastertouch" action actually stopped the hammer
firmly before reaching the string.  I had to get my
flashlight and look to see if there was a block of
wood between the hammer shank and the damper.  That's
what it felt like when the hammer stopped.  The
backcheck arm (for lack of a better term) was grabbing
the jack so firmly it stopped the hammer butt as if
there was a block of wood in front of it.  

I screwed in the regulating button on the arm, which
raises it away from the jack.  That gave the hammer
enough freedom to reach the string.  But I could not
predict how the checking distance would respond to the
movement of that button.  I just got each note to work
and had to be satisfied with that.  

The action did feel nice when I was done, and seems to
have held up very well after 90 years.  I would like
to know more about it for my next visit.  


Greg Graham
Brodheadsville, PA

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