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Re: [PSUBS-MAILIST] Thermoforming acrylic sheet (domes)
Hi Brian,
My understanding is that machine process creates stresses in the
material. Annealing after machining will help relieve the stresses. To
have a relatively dimensionally stable piece of material that will hold
its diminsions after the annealing process a pre-machining annealing
process helps to take the shrinkage out. Whether you will still get
significant shrinkage from the post-machining annealing I do not know.
Regards,
Ray
atozed@juno.com wrote:
> The book says do it, I would.
> -Peter Korwin
>
> On Tue, 7 Dec 2004 14:13:19 -0800 "Brian Cox" <ojaibees@ojai.net
> <mailto:ojaibees@ojai.net>> writes:
>
> *Hi All, *
> * With my "doughnut" acrylic viewport all I plan to do
> is purchase a 24"x24"x4" and then cut a inside diameter of 20" and a
> outside diameter of 24" thus having a 2" thick viewport to look
> through. This will give me a 360 degree view but only 4" high.
> Does anyone know if I need to heat this piece of acrylic up first
> before I cut it so that any shrinkage that accurs will not change my
> dimensions? According to the infor below that would seem to be the
> case. Then would I need to heat it again after it has been cut?
> Maybe I don't need to heat is at all?*
> *//*
> *//*
> */Shrinkage
> /*Because of the orientation imparted during manufacture, acrylic
> sheet shrinks slightly when heated to thermoforming temperatures.
> Manufacturing direction can be determined from the sheet label or
> print on the masking. The lines of print are perpendicular to the
> direction of manufacture.
>
> Original dimensions won't change in fabrication operations not
> requiring heat. However, sheet heated to thermoforming temperature
> changes dimensionally by about 3 percent maximum shrinkage in the
> manufacturing direction and approximately 0.5 percent maximum width
> increase (transverse direction).
>
> Measure the shrinkage in a preliminary test, if acrylic sheet isn't
> held in a retaining frame. Then, determine the size of material
> required to compensate for shrinkage before cutting any blanks.
>
>
>
> Regards
>
> Brian Cox
>
> ----- Original Message -----
> *From:* Thijs Struijs <mailto:thijs-struijs@planet.nl>
> *To:* PSUBS <mailto:personal_submersibles@psubs.org>
> *Sent:* Tuesday, December 07, 2004 1:01 PM
> *Subject:* [PSUBS-MAILIST] Thermoforming acrylic sheet (domes)
>
> www.designnews.com/article/CA85859.html
> <http://www.designnews.com/article/CA85859.html>
>
> Thijs Struijs
>
>
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