Spurlock shimming method.-last

[JIMRPT@AOL.COM]

In a message dated 5/07/2001 1:53:39 AM, Tom C. wrote:

<<"I'd be tempted to poke a hole in your balloon analogy. The board will
swell up as it regains moisture, but I'm not so sure about the glue line
swelling.">>
 OK I can take some hole poking cause I admitted my analogy wasn't 'air 
tight' to begin with.:-)  But if the glue line doesn't expand and contract 
with the board then should there be any question as to where 'some' "cracks" 
along shim lines come from? If there is a moving force operating on a joint 
between a flexible/plastic surface and a non-flexible/plastic surface won't 
the "crack form at the interface/shim line of the two surfaces? 


<<"My take is that the joint between two boards, or board and
shim, takes a beating because of not only the pressure of the expanding
pithy stuff, but the dissimilar rates of expansion of juxtaposed
members. However, that doesn't seem to explain compression ridges.">>

 Well my take is that it does exactly explain the "compression ridges". At a 
panel junction it seems that the less dense panel suffers the most 
compression/distortion due to cellular destruction/malformation than does the 
more dense panel. Differring expansion/contraction rates also come into the 
equation which adds to the effect I suppose.

IMO:
Finally..... 
a.) Shims developing cracks comes from improperly prepared cracks. Cracks 
that are not prepared in such a way as to be shimming on 'relatively' 
undamaged wood are 'pre-cracked' so to speak. :-)
b.) A shim/crack that is properly prepared at the lowest point of a boards 
contraction cycle will be exposed to more "pressure" at the boards highest 
expansion cycle......more "pressure" equates to my mind as being the same as 
'more propensity' to re-crack along the glue line.
c.) Shimming is a real alternative to replacing the entire board. Replacing a 
board simply because a few glue lines have failed, or cracks developed, does 
not make sense 'if' all the other factors in board evaluation are positive.

 It is alright with me for others to have differring opinions...that does not 
needfully make any of us less right or wrong.
Jim Bryant (FL)
p.s. Of course if Del would hurry and finish his research/development work we 
could shift our discussion from shims to some other facet of soundboard 
erratum problems. :-)