Thanks,...There seems to be a lot of useful information on their site, especially about technical properties. I am certainly interested in their pages on forming thermoplastics.

Joseph

Joe,

Start here

Regards,

One Sky Dog

_http://www.chemcastacrylics.com/technical/mx4.htm_
(http://www.chemcastacrylics.com/technical/mx4.htm)

Joseph,

I formed my transparent fuel guages from Lexan (polycarbonate) and
they worked perfectly first time.

First the caveats. Acrylic (perspex)is easier to form, is harder,
more prone to cracking and is much less strong. It will blow or
vacuum form with ease, provided you follow some simple rules. It is
also available in a multitude of colours - which lexan is not.

If you use a mold, male or female, the quality of finished product is
entirely dependent upon the finish of the mold. You want a mirror
finish? The mold must have one.

If you blow or vacuum form the final shape is determined by two factors :

1. the plan view of the "holder" i.e. circular results in a
hemisphere, pear shape results in a teardrop, etc.

2. the pressure differential which determines the finished height.

Because there is nothing touching the surface, you get a mirror
finish and good optical qualities by default.

For acrylic, the trick is to hold the blank sheet - typically 3 mm
securely in a frame whilst it is heated. The exact temperature can be
found from the manufacturer's web site or the product sheet. It is
evenly and slowly heated until it sags under its own weight. The
frame is then sealed and clamped to the air / vacuum source and the
pressure briskly increased/ decreased until the desired hieght / depth
is reached.

The pressure is held until the part cools. The frame is then
unclamped, the final shape released from the frame and the excess cut
away with a dremel and grinding wheel. It is a good idea to mask the
edge of the cut with tape. Support both sides by frequent taping acoss
the cut. Warm everything before cutting.

For stretch forming, which is most appropriate for lexan, the first
trick is to realise that it is very prone to absorbing moisture which
manifests itself as bubbles in the finished product. For this reason
it vital to preheat and prepare the material for some time - typically
30 minutes prior to preforming.

I used metal tools because it was easier to get the clearances and the
finish I wanted. These I also put in the temperature controlled oven
and brought them up to temperature. Again the temperature is
important and is such that the blank is like uncooked pastry - floppy.

When I was ready, armed with the leather gloves, I removed the bottom
form onto a nearby bench, quickly laid the blank over the form - it
draped well, and then quickly forced the external ring down over the
bottom form and the blank to get the sharp transitions I required.

It cooled quickly, is very tough - hit it with hammer tough. and
easily trimmed.

Hope this helps

Regards

John



I


--- In Q-LIST@..., "Joseph Snow" <1flashq@...> wrote:

I am getting ready to install Nav lights in the Main wing tips and

atop the vertical stabilizer. I will be carving the wing tips and top
of the vertical stabilizer from blue foam; then, covering with a 2
layers of BID. I then want to make custom clear plastic lens where
the position light will be installed.

I remember someone on the list describing how the lens were made.

It seems the clear plastic is heated to about 300 deg., then forced
over the part or a mold of the part to stretch and form the clear
plastic. After cooling, the formed plastic is trimmed and installed.

Has anyone on the list done something like this? Can you point me

to a detailed description, perhaps in Q-talk, on the Web, a book or
article? What type of plastic?

How thick originally? Temperature? Etc.

Thanks,

Joseph Snow

[Non-text portions of this message have been removed]

Dave Ekstrom here:

dekstrom@...

http://www.ultralightsoaringaviation.com
<http://www.ultralightsoaringaviation.com/>





_____

From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
Mark A. Pearson
Sent: Monday, August 07, 2006 9:09 PM
To: Q-LIST@...
Subject: Re: [Q-LIST] Custom Wing Tips



Sam (Hoskins), do you have Dave Eksrom's address, he can do this or describe
how it's done. I lost his address the last time I had to deal with a worm or
something.

Mark Pearson

Tony Bingelis has 5 pages on "Working with Acrylics" in "The Sport Plane
Builder." One section deals with "drape-forming" plexiglass in the home
oven. Also has installation, drilling and other tips.

Mike Perry

Sam (Hoskins), do you have Dave Eksrom's address, he can do this or describe how it's done. I lost his address the last time I had to deal with a worm or something.

Mark Pearson

Companies like the _Aircraft Windshield Company_
(http://rds.yahoo.com/_ylt=A0oGkjse6ddEH.4A2YhXNyoA;_ylu=X3oDMTBxbnNibGg1BGNvbG8DdwRzZWMDc2MEdnRpZANGNjY1Xz
k5/SIG=170p24qhn/EXP=1155087006/**http://local.yahoo.com/details?fr=dd-local-t
l1&id=20566456&stx=aircraft+windshield+company&csz=Los+Alamitos+CA&ed=FNuYn616
0Swp1owPbCQmDG0kdo.A14yYPcTEvluYJGxt_gc3lLEUq96TmliCa37E1e5tKsc-) - (562)
430-8108 - 10871 Kyle St, Los Alamitos, CA - routinely carry molds of various
aircraft canopies and window. They stretch plexi all the time. Once, I had a
custom part built for my motorcycle windscreen. There are probably a
number of places near you that could assist. If you make a nice internal mold
shape, it probably would not amount to much to get them to warm up some material
and stretch a part. It only requires a convex mold side.

Phil Lankford

I am getting ready to install Nav lights in the Main wing tips and atop the vertical stabilizer. I will be carving the wing tips and top of the vertical stabilizer from blue foam; then, covering with a 2 layers of BID. I then want to make custom clear plastic lens where the position light will be installed.

I remember someone on the list describing how the lens were made. It seems the clear plastic is heated to about 300 deg., then forced over the part or a mold of the part to stretch and form the clear plastic. After cooling, the formed plastic is trimmed and installed.

Has anyone on the list done something like this? Can you point me to a detailed description, perhaps in Q-talk, on the Web, a book or article? What type of plastic?
How thick originally? Temperature? Etc.

Thanks,

Joseph Snow