Author: vboboe
Date: 2006-07-23 18:41
... good point, wrowand, it probably should have read 'extreme expansion and contraction', and the bit about cracks was poorly placed in the same sentence without adequate qualification, this isn't really what i meant, sorry folks
... had better try to clarify my understanding on this matter, please bear with me
The weather is hot right now, so immediate issue at hand is keeping oboe within a reasonable temperature range, emphasis on what's the top end of the range -- possibly about 40C / 102F -- after that, getting extreme, but grenadilla wood itself can probably handle hotter than that
Car parked in summer will heat up rapidly and go off my own car interior themometer at top end 60C / 130F, so no idea how much hotter than that it really is, and we're talking moist Pacific west coast marine environment, not an even greater extreme such as arid and super-hot Death Valley desert conditions
... my current understanding is that extreme expansion or contraction of metal in post-holes, frequently enough, LOOSENS posts. (Extreme contraction includes very cold conditions, but we're in the hot season) Superhot metal posts in contact with wood post holes rapidly dries out the wood snugly adjacent to them, and dry wood shrinks. Dry wood cracks more readily than moist wood.
And, when discussing well seasoned grenadilla which is a dense and quite dry (albeit resinous) wood to begin with, 'dry' and 'moist' are only comparative words.
Hopefully nobody's abusing their oboe in this manner, over-heated once only may not be a problem, but several times might, especially if the wood isn't being oiled or humidified adequately enough -- should immediately clarify here that local playing conditions determine advisable frequency of oiling or humidifying -- oil helps resist excess atmospheric moisture, humidifying helps wood survive excess atmospheric dryness, and oil helps keep humidified wood moist longer
wrowand writes
<<The coefficient of thermal expansion for nickel silver is on the order of
0.00002 mm/mm/degC which means that even over a 30 deg temperature range, it would only change 0.06%>>
Seems worthwhile commenting here that the diameter of post-holes is small (somebody else please provide size & do the math, don't have time to research it just now) and 0.06% metal expansion over 30 degree temp range in that small space would equal what ***percentage*** expansion in the post-hole?
In some places on the oboe post holes are set very close to vents (G#, D trill), and my current understanding is that the G# position in particular is a fairly common place for cracks ... therefore, to my mind, it's not unreasonable to intuitively presume that post expansion next to the G# key in particular would hasten any potential to crack there ... especially since this key is in frequent use and applies considerable torque on each of its support posts every time it's used
general principal i like to remember -- storing anything made of wood in extreme heat dries out the wood excessively, which can lead to cracking and splitting anywhere cut wood fibre ends are exposed, such as toneholes.
As for the plastic liner concept, Buffet Greenline and others, i'm very cautious about this innovative solution to resist cracking. My experience with anything plastic lined is that, over a period of time, plastic separates or degrades, it just cannot stay bonded or perfectly intact indefinitely, and once it starts bubbling, peeling or flaking off in the bore, oboe's toast. We may be talking 20-30 years ... or only 5 if the oboe endures excessive heat treatment
... which is why methinks first year oboe player lucyw want want to err on the side of comfortable caution to protect her gorgeously beautiful new instrument (and please, lucyw, don't worry about the plastic liner :-)
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