Action flange crushing

[Phillip Ford]

>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