Author: Chris P
Date: 2011-10-10 12:02
Keywork doesn't expand or contract anywhere near as wood or plastic does, plus the pillars only screwed 4mm into the joints.
On an S40c (and S% and XL-Z), the joint diameter at the top just beneath the crown is 22mm and the bore diameter is 3.9mm at that point, so there's plenty of wall thickness between the ends of the pillars screwed 4mm into the joint wall and the bore if you draw a diagram using these measurements.
Stresses on the joints of wooden instruments aren't longitudinal ones, they're outward forces exerted from the bore to the outside diameter so any keys mounted between pillars that run across the joints will be the first ones to suffer and they're the keys with the shortest key barrels - as the outside diameter expands or contracts with humidity, the pillars also move outwards or inwards which can cause these keys to bind, so the lower 8ve key and F vent are usually the ones that bind up first. Long keys mounted between pillars running along the length of the joint aren't affected as wood will expand and contract widthways more than it does lengthways.
On plastic instruments, thermal expansion/contraction is more pronounced and happens in all directions, so all keys have the potential of binding up when cold.
Former oboe finisher
Howarth of London
1998 - 2010
The opinions I express are my own.
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