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

[tmsmalley@usinternet.com]

If I recall correctly in the Kent Markham semi wet sub plans - he recommended using air to inflate the warm plastic using a collar and schrader valve - and have a flat metal sheet for the plastic to push against in front to make a flat area to see through that wouldn't have the distortion of a semispherical bubble. Of course this was 30 years ago and ambient pressure sub!
Tim


>
>From: "Dan H." <machine@epix.net>
>Date: Wed, 02 Jan 2002 08:54:43 -0500
>To: personal_submersibles@psubs.org
>Subject: Re: [PSUBS-MAILIST] First post -Acrylic Canopy design forming
>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
>>
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