In a message dated 6/8/2003 5:40:54 PM Eastern Daylight Time,
Tim@houlihan.flyer.co.uk writes:
> Paper changes its dimensions with temp and humidity like you would not
> believe.
> Some design offices plot onto Mylar or polyester material to minimise the
> problem
Paper changes its dimensions with temp and humidity like you would not
believe.
Some design offices plot onto Mylar or polyester material to minimise the
problem
Oh, I believe it. However, I don't think the 1/4"-3/8" on average size
change, not always shrinking, is necessarily all caused by the paper. Mylar
templates would be the answer, but not drawn on, but rather cut full scale where
they
could easily be used to trace the pattern onto whatever material is being cut
to shape. Mylar templates could easily and cheaply be computer cut much like
the vinyl graphics that are commonly seen on Europa's. Accuracy would not be an
issue.
Blueprinting the templates full size, as many other kit manufacturers do,
would certainly be a help. It's been my experience, from working in a metal
fabrication shop where we routinely used blueprints to make parts, that
blueprinted
templates are much more accurate than inexpensive photocopy paper. It also
has to do with the copier machine quality the blueprint was made on in the first
place. "Real" blueprint paper is much thicker and more dense than photocopy
paper, therefore it doesn't "move" like thin photocopy paper used in the
manual. Of course, I've also seen newsprint used for blueprints as well which
was
entirely unacceptable. Not saying that "real" blueprint paper doesn't change,
just not as much as I've noticed from the photocopied pages in my manual.
Whether or not blueprints are used for scaling parts for fabrication has more to
do
with what level of accuracy is needed. In our case, were accuracy is held to
1-2mm, they would work fine. If accuracy to .0001 mm were needed it would be a
different ballgame. The size differential I've experienced probably has more
to do with whether the templates in the maunals are copies of copies or copies
of originals and how accurate the originals were in the first place.
At any rate, I've spent a whole lot of time making sure parts fit correctly
and so far, roughly 700 hours into the kit, not one single template has been
accurate. I've learned to shape each part a little oversized out of 3 mm ply and
sand to fit, then transfer the shape to the actual material for the part. The
supplied templates act as a rough guide to the shape of the part being
fabricated, but their accuracy leaves a whole lot to be desired. Ah, but, what
the
hell, we're only building an airplane!
Regards,
John Lawton
Dunlap, TN
A-245
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