Re: [PSUBS-MAILIST] First post -Acrylic Canopy design forming

["Dan H." <machine@epix.net>]

Ashman,
Your heading in the right direction with your method, heat an acrylic, but
there's more to it than that.

BUT!!!!  First of all I have to ask;  Did you do any research about what this
viewport will withstand?  I know you wrote:
"P.S i know some of you are wondering about the thickness, this submersible
is not designed for deep depths, and the thickness is not a concern."
Unless your building a wet sub, it's a BIG concern and even a wet sub has
pressure differences.

There are standards for viewports, but I don't think you'll find one listed with
the design your looking for.  Before you dive your sub with this design, be sure
to test it to at least twice your max. diving depth, WITHOUT  YOU inside.

As far as forming acrylic, your on the right track, but you need an convection
oven to do it well.  Another thing that might be helpful is to purchase a piece
of polished stainless steel, or at least a smooth piece of thin steel sheet that
you can flex to the shape and be mounted to keeps this shape for a mold of the
inside of your curve.   Place this mold with your acrylic sheet over top of it
in a convection oven so it will heat uniformly.  Some weight or pull downs might
be needed depending on how much curve your looking for.  To do this job properly
you need an oven with precise temperature controls so you can control the cool
down process.  Even the heating should be done in increments, but it must be
cooled at a slow rate to reduce internal stresses.

Also keep in mind that the acrylic will shrink a little in size when you do
this.  Not much, but if you have some leeway with your finished size it will
help.  You can also trim to size after the bending but than you have to do
another oven process to stress relieve it.  Before using your mold you should
sprinkle it with a light dusting of talcum powder to enable the acrylic to creep
across the mold surface as needed.  Don't apply to much because any talc left in
a lump will show up in the surface finish of the acrylic.  You might want to do
some experimenting on one or two till you get your method fined tuned.  The
material isn't that expensive.

You probably could bend the acrylic with a heat strip as you mentioned but
you'll never hold an exact curvature by hand.  The hotter the area, the easier
it bends, and it's almost impossible to heat the sheet evenly by hand.  But,
probably the most important thing is the stress relieving process that has to
follow your bending or cutting.  The last thing that must follow any operation
that applies heat of any kind, cutting, drilling etc., is a stress relieving.
That takes hours and hours in a convection oven.  The total time depends on the
thickness your using and the temp you heating to. The forming temp is higher
than the stress relieving temp.

Get yourself a copy of PVHO.  It's the standards for "pressure vessel for human
occupation" design.  In there is a section about viewports and the information
you'll need to design a viewport and stress relieve it.  Don't expect to find
the shape your creating because you won't find it as an approved design, but the
acrylic information might help you.

Good luck and remember don't guess if it's going to hold at depth, calculate and
test it.

Ashman Vi wrote:

> Hello everyone at PSubs. And a Happy New year to you all.
>
> I have often visited your site, and browsed through your Archives, and the
> conversations regarding information and advice is brilliant.
>
> I have a question for you guys, that i hope some of you may be able to help
> answer.
>
> Question: Im looking to make a canopy for a submersible out of clear
> acrylic, or other plastic material.
>
> The thickness of the canopy would be around 1/2 inch thick.  What im
> wondering is, how could i form my own canopy from acrylic.  Guaranteed,
> there is not an existing mould around for the form i want. The shape is
> almost a flat window with a slight curvature, would it be better to buy a
> certain amount of pre-made flat acrylic and heating it to required form? and
> cutting to the desired dimensions? the surface area isnt all the big either.
>
> Lets say i have a surface which has the required curvature, and i was to
> place the said pre-made acrylic on it, and use say a " heat blower " from a
> wall stripper, or a portable electric heater. Or another heating device to
> soften the plastic. Would this work, and is there any other methods? also,
> how hot would the arcylic need to be for it to be able to be maluable
>
> Has anyone tried making anything like this on their own in Psubs?
>
> P.S i know some of you are wondering about the thickness, this submersible
> is not designed for deep depths, and the thickness is not a concern.
>
> Sincerely
> AshmanVi
>
> _________________________________________________________________
> MSN Photos is the easiest way to share and print your photos:
> http://photos.msn.com/support/worldwide.aspx