Seasonal pitch change:

[RicB]

Hi Jason

Everything reacts to temperature changes. Metal does too.  So no doubt 
the plate does change its dimensions some. But no-one has even come 
close to measuring the effect this eventually has on tunings. Nor has 
anyone looked at what degree any change in rim height, or other case 
dimensions can effect tuning.

In the end tho basically one (or both) of two things can happen seen 
from the strings perspective.  Either the speaking length is altered due 
to a shift in the relative positions of the two terminations to one 
another, or something can cause a change in the over length of the 
string.  A tilt in the bridge could effect the former, bridge deflection 
changes can affect the later.  Pin block tilting could also effect the 
later tho I dont think anyone has shown this actually does happen.

My approach is to take a look at what results in any specific assumed 
change.  And both of the ones we've looked at so far dont seem to 
account for the pattern of out of tuneness that we see occuring.  I cant 
help but thinking that there is something more significant going on at 
bridge endpoints and breaks then has been tabled so far.  But who knows ?

Cheers
RicB


    At the risk of sounding stupid, I am compelled to ask again: Does the
    cast-iron plate change its dimensions with temperature changes? The
    distance
    from tuning to hitch pins might change just as railroad tracks
    shrink and
    swell in length - no? I'm just thinking it must be a contributing
    factor.

    Jason