Forwarded Message from Ken Martindale

[Jonathan Wallace <jon@whoweb.com>]

Hello Ray,

I got your paper on the window forming and here is my comments and
experience. My Sub is a one man wet Sub.

Here is my experience on forming a window for my Sub. I bought a sheet
of Polycarbonate 1/4 inch thick from Home Depot here in Melbourne,Fl. I
then cut a circle out about 22 inches in diameter which was the largest my
wife's oven would take. I then bought a Wok (that's right, a Wok!). I
polished the bottom of the Wok for my mold with the idea that I would let
the polycarbonate flow around the Wok to get close enough the my
requirements.

I then experimented with several smaller pieces in the oven to see what
temperatures were needed to dry the plastic out before reaching the
flowing temperature. I found that at least one day at 212 F was needed to
remove the absorbed water in the plastic. I believe the plastic will absorb
water directly from the atmosphere.

I then placed the circle of polycarbonate above and on the Wok in the
oven. I set the temperature at 200 F and left it in for three days. At the
end of this time I raised the temperature control on the oven towards 380 F
until the plastic flowed around the Wok.

Here was the results:

1) The plastic also flowed around the wife's oven grates.

2) I still got some bubbles in the plastic.

3) I ended up with a useable( marginally) window which I have not
polished.

4) My Wife, when she found me grinding the polycarbonate off the grates,
soured a little on the idea of a Sub.

5) I decided to use the window only if I could not do better. Recently I
talked to Florida Technology and found they used a company here in
Melbourne called "Viplex". I intend to contact them but haven't done so yet.

My experience is consistant with your comments in your paper. I would
like to add that the temperature sensor in my Wife's oven is located at the
top of the oven and when I blocked the lower part of the oven with the
Wok, the oven temperature tended to go out of sight. I feel that if a fan,
as you mentioned, were added that the home oven would work. My
experience with the temperature control was that it was adequate but the 
fan would help considerably. I was able to watch the plastic through the oven
window and when I saw the plastic begin to flow I turned the temperature
down.

 I do not recommend this as a viable technique and agree with your
comments you currently have in your paper. I would suggest that you add drying
temperatures and forming temperatures for polycarbonate and acrylic if
you can find a reference.

I am also considering making my own oven, larger, with a fan and a
precision temperature control. I would opt for the Droop forming if the window
dimensions were not too critical.

The reason I am not doing too much on the window now is that I am
designing and building the motor control electronics. I am finding this a lot
easier as I have a background in power electronics.

The last major problem is floatation which I think I have solved with
floation balls from Flotech.

Good luck with your paper.

Ken Martindale