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January 1997

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Subject:
From:
Paul Gould <[log in to unmask]>
Date:
Tue, 21 Jan 1997 18:13:50 +0000
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Your absolutely right, warp direction must be consistent through all
layers of the construction and bow will definitely occur if warps are
crossed. This bow is impossible to remove.

In message <[log in to unmask]>, Bob
McGarry <[log in to unmask]> writes
>
>
>      The issue came up this morning with a customer of mine as to why I 
>would want  to deviate from his specification calling for alternating 
>the grain direction in the layup of a  6 layer MLB. I could'nt give 
>him  the answer he was looking for. It seems that in all his 
>experiences,  other vendors require cross graining to avoid warp and 
>twist and that  keeping grain direction constant was a no, no.
>     In all of my experiences the case has been just the opposite. WE 
>go out of our way to assure that materials are cut to order in the 
>proper direction so we can avoid cross graining. Maybe this practice 
>started years ago by recommendation of our laminate supplier, or 
>maybe after making many orders of  "potato chip" boards we decided to 
>watch the grain directions of our layups.
>     My thoughts on the advantages of  NOT cross graining are:
>1. Predicable  shrinkage compensated by scaling the artwork.
>2. No built in stresses from lamination thus less twist, warp in 
>subsequent processes.
>
>
>Can anyone  please ellaborate on this issue.
>
>Thank You.
>
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-- 
Paul Gould

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