Action flange crushing

[Dean May]

I always tighten flange screws to near the point of stripping the screw. I
never bother to check to see if the flange is "crushed" or not. I have never
had one come loose that I have tightened like this.

Caveat Emptor: 25 year anecdotal evidence only. Your results may vary.

Dean
Dean May             cell 812.239.3359
PianoRebuilders.com   812.235.5272
Terre Haute IN  47802

-----Original Message-----
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On Behalf
Of Phillip Ford
Sent: Saturday, November 20, 2004 11:29 AM
To: Pianotech
Subject: Re: Action flange crushing

>Phil,
>
>I don't understand.
>
>>>I am continuing to investigate action screw torque.  One thing
>>>that has turned up on some correspondence is the admonition not to
>>>crush the flange. Any thoughts on why this is a bad idea, other
>>>than aesthetics?
>
>Why would you "want" to crush the flange and cause damage? If one
>does, sooner or later, it's going to cause a problem. JMHO.
>
>Avery

Perhaps I should have started this whole thing out by defining what I
mean by crushing.  I mean any permanent deformation of the flange.
If you remove the flange you can see an indentation where the screw
head was or where the flange contacted the rail.  I don't mean
torquing the screw down until the flange cracks or breaks.

I would 'want' to crush the flange if someone showed me some data
that flanges that have been slightly deformed or preloaded actually
have less tendency to get loose with changing humidity.  I would want
to carefully avoid it if  someone showed me data indicating the
reverse.

If it really is important not to have any permanent deformation of
the flange then one way to avoid it might be with a torque limit.
The problem with a torque limit is that it has to take into account
tightness of the screw in the rail, the compressive yield strength of
the particular flange (which will depend on the material it's made
from, and if it's wood will depend on what tree it came from, what
section of the tree, how it was cut, and how it was aged), etc.

I know that there are many people out there rolling their eyes
because I'm posting on this topic (just make the screws tight enough
and shut up), but it amazes me that on something this basic there
seems to be no industry specs or data.  This topic is like most piano
topics (such, as we have recently seen, wound trichords) - you can
find many people willing to give you, in an authoritative voice, a
'definitive' answer.  It's hard to find many that can offer a
convincing reason to go with it, and fewer still who can offer any
data, evidence, or experience to back up that reason.  (Thanks to
those that have offered examples of problems with overtorqued flanges
in service).  If you were to ask me how tight the hammer flange
center should be, and I responded - tight enough, but not too tight
(gram gages are for amateurs) - would you consider that a meaningful
response?  And if I gave you a gram reading, or number of swings, and
you asked me where that number came from and I responded - well, it
seems right to me, and I have over twenty years of experience in this
field - would you consider that a meaningful response?

I think much investigation into this topic would quickly show that
wooden flanges and wooden rails (or at least wood screws into wooden
rails) are a bad idea with regard to consistent action screw torque,
assurance of no flange damage in the short or long term, and long
term flange tightness.  Perhaps most people would prefer not to know
(except Kawai, of course).

I will finish this by asking you why, in your opinion, is crushing
the flange going to cause a problem (and what would be the nature of
that problem) sooner or later?

Phil Ford
_______________________________________________
pianotech list info: https://www.moypiano.com/resources/#archives