Re: [PSUBS-MAILIST] Thermoforming acrylic sheet (domes)

[Ray Keefer <Ray.Keefer@Sun.COM>]

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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