overcentering justified?

[David Love]

Bob:

I have found it awkward to measure the center pin height as well.  The
method I now use incorporates the Jaras String height gauge as well.  That
way, the string height and center pin height are taken with the same
measuring device and even if the absolute measurement is off, it is the net
difference that counts and it will be correct.  To measure the center pin
height, place a straightedge along the top of the hammer flanges extending 
out over the end of the action (I take measurements from both the bass and
treble end BTW--sometimes they are different).  Now place the Jaras gauge
under the straight edge along side the action and take the reading.  Then
measure the distance from the top of the flange to the center of the center
pin and subtract that from your initial measurement.  That will be your
center pin height. 

David Love
davidlovepianos@earthlink.net


----- Original Message ----- 
From: Bob Hull 
To: davidlovepianos@earthlink.net;Pianotech
Sent: 8/21/2003 7:19:55 PM 
Subject: Re: overcentering justified?


I have carefully checked my Jaras string ht. gauge and it is right on.  I
need to come up with a better rig for measuring the flange center pin ht. -
something more stable, but I don't think I have a faulty measurement there.
The string rises ( different strings rise at different rates) as it goes
toward the bridge.  I have wondered if the action rail could change height
in the middle compared to the ends where I measured.  
Humidity changes could cause a very slight change in string ht as the
bridge rises but not enough to affect regulation I suppose.  If center rail
glides are down to far they could affect flange center pin ht.     

I bored some new hammers at 48 mm bore distance and they regulated well. 
They were able to have 45mm blow, .390 (9.9) dip, and .030 aftertouch.  So,
I guess that's the bore distance I'll use.  Thanks for all your help.

Bob

David Love <davidlovepianos@earthlink.net> wrote:
Perhaps your string height measuring device is improperly calibrated. Or,
you measured the flange center pin height incorrectly, or both. The only
other possibility is that the strings run downhill to the bridge by the
amount of the difference. That doesn't seem likely. 

David Love
davidlovepianos@earthlink.net


----- Original Message ----- 
From: Bob Hull 
To: Piano tech
Sent: 8/21/2003 8:03:08 AM 
Subject: Re: overcentering justified?


When I measured the distance from the key bed (workbench) to the hammer
flange center pin and subtracted it from the string height near the hammer
strike point, why did it give me a 2" (50.8 mm) difference? This is a
different indication of bore distance from when I put a line level on a
hammer shank and compared a 50.8mm bore distance to a level on the strings.
The 50.8mm bore shows that when the hammer is raised to the string the
bubble indicates a slightly undercentering. The old 48 mm bore shows a
shank that has almost exactly at the same level (slight rise) as the
string. 

Since the string ht. was measured at a distance about 130mm (length of
shank to center of hammer molding) away from the center pin ht. it seems
like it should have indicated
the same distance as the level/bubble comparison test. ???

Why didn't it? Any ideas?



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