Making plastic parts

"cavelamb himself" wrote in message
...
Peter Dohm wrote:

Actually, I did have a car a while back with one of those rear window
brake
lights that eventually failed. For no obvious reason, the replacement
bulb
(of the same physical size and generic part number) quickly burned
through
the top of the plastic casing--despite having a peice of foil (which was
original equipment) directly above the bulb. That was also in the 1amp
range at 12-14 volts; but I believe that the clearance was closer to a
quarter inch.

A strobe should generate much less heat, especially localized heat, than
an
incandescent bulb; but this is a good problem to keep in mind for nav
lights. Of course, LEDs have become an affordable and reliable
alternative
that also eliminate much of the heating problem--especially if the
current
source is remotely located.

Peter



Peter,

I just happened to have the plug and one of the "experiments" on hand.

Guess I need to revise the clearance question to LESS than 1/2 inch.

This one, I believe, is polycarbinate (DUE TO THE LACK OF BUBBLES IN THE
PLASTIC).

The lexan attempts were made with .065 scrap from my windshield.
Every one of those bubbled like crazy in the baking phase.

Lexan is hydroscopic and retains considerable water.
This stuff "boils" out while heating unless "baked" out at below 212
for several hours. It was kinda pretty with the colored light on inside
it. But not exactly the sleek smooth aircraft parts I had in mind...

Pic at:
http://www.home.earthlink.net/~cavel...sc.htm#wingtip

More clearance, thicker plastic, maybe they use some kind of special
stuff - I really dunno there.

Just that thin stuff with a fairly hot bulb simply didn't work...

YMMV

Richard

I am not really sure why, but I was thinking of the type of lens that ends
up being an entire corner of a wing, so that it has a lot of volume and a
lot of area. Now that I have thought about it, 12 to 14 watts is a *lot* of
heat for this size lens.

I am not sure what material is used in the currently offered commercial
assemblies, but it may very well be glass. (As you might guess, I also
don't know what material to use as a mold for glass--much less how to form
the resulting mold.)

Peter

Peter Dohm wrote:
"cavelamb himself" wrote in message
...

Peter Dohm wrote:

Actually, I did have a car a while back with one of those rear window

brake

lights that eventually failed. For no obvious reason, the replacement

bulb

(of the same physical size and generic part number) quickly burned

through

the top of the plastic casing--despite having a peice of foil (which was
original equipment) directly above the bulb. That was also in the 1amp
range at 12-14 volts; but I believe that the clearance was closer to a
quarter inch.

A strobe should generate much less heat, especially localized heat, than

an

incandescent bulb; but this is a good problem to keep in mind for nav
lights. Of course, LEDs have become an affordable and reliable

alternative

that also eliminate much of the heating problem--especially if the

current

source is remotely located.

Peter



Peter,

I just happened to have the plug and one of the "experiments" on hand.

Guess I need to revise the clearance question to LESS than 1/2 inch.

This one, I believe, is polycarbinate (DUE TO THE LACK OF BUBBLES IN THE
PLASTIC).

The lexan attempts were made with .065 scrap from my windshield.
Every one of those bubbled like crazy in the baking phase.

Lexan is hydroscopic and retains considerable water.
This stuff "boils" out while heating unless "baked" out at below 212
for several hours. It was kinda pretty with the colored light on inside
it. But not exactly the sleek smooth aircraft parts I had in mind...

Pic at:
http://www.home.earthlink.net/~cavel...sc.htm#wingtip

More clearance, thicker plastic, maybe they use some kind of special
stuff - I really dunno there.

Just that thin stuff with a fairly hot bulb simply didn't work...

YMMV

Richard


I am not really sure why, but I was thinking of the type of lens that ends
up being an entire corner of a wing, so that it has a lot of volume and a
lot of area. Now that I have thought about it, 12 to 14 watts is a *lot* of
heat for this size lens.

I am not sure what material is used in the currently offered commercial
assemblies, but it may very well be glass. (As you might guess, I also
don't know what material to use as a mold for glass--much less how to form
the resulting mold.)

Peter




Well, I think we know it has been done before.
I know I've seen those corner style covers.

But the details?

Might be I was just too close and too thin for the amount of heat.

Continue researching this, Peter.

Like my Ex was fond of saying..."Three weeks in the lab will save you
4 days in the library every time".

Richard

"cavelamb himself" wrote in message
...
Peter Dohm wrote:
"cavelamb himself" wrote in message
...

Peter Dohm wrote:

Actually, I did have a car a while back with one of those rear window

brake

lights that eventually failed. For no obvious reason, the replacement

bulb

(of the same physical size and generic part number) quickly burned

through

the top of the plastic casing--despite having a peice of foil (which
was
original equipment) directly above the bulb. That was also in the 1amp
range at 12-14 volts; but I believe that the clearance was closer to a
quarter inch.

A strobe should generate much less heat, especially localized heat,
than

an

incandescent bulb; but this is a good problem to keep in mind for nav
lights. Of course, LEDs have become an affordable and reliable

alternative

that also eliminate much of the heating problem--especially if the

current

source is remotely located.

Peter



Peter,

I just happened to have the plug and one of the "experiments" on hand.

Guess I need to revise the clearance question to LESS than 1/2 inch.

This one, I believe, is polycarbinate (DUE TO THE LACK OF BUBBLES IN THE
PLASTIC).

The lexan attempts were made with .065 scrap from my windshield.
Every one of those bubbled like crazy in the baking phase.

Lexan is hydroscopic and retains considerable water.
This stuff "boils" out while heating unless "baked" out at below 212
for several hours. It was kinda pretty with the colored light on inside
it. But not exactly the sleek smooth aircraft parts I had in mind...

Pic at:
http://www.home.earthlink.net/~cavel...sc.htm#wingtip

More clearance, thicker plastic, maybe they use some kind of special
stuff - I really dunno there.

Just that thin stuff with a fairly hot bulb simply didn't work...

YMMV

Richard


I am not really sure why, but I was thinking of the type of lens that
ends
up being an entire corner of a wing, so that it has a lot of volume and
a
lot of area. Now that I have thought about it, 12 to 14 watts is a
*lot* of
heat for this size lens.

I am not sure what material is used in the currently offered commercial
assemblies, but it may very well be glass. (As you might guess, I also
don't know what material to use as a mold for glass--much less how to
form
the resulting mold.)

Peter




Well, I think we know it has been done before.
I know I've seen those corner style covers.

But the details?

Might be I was just too close and too thin for the amount of heat.

Continue researching this, Peter.

Like my Ex was fond of saying..."Three weeks in the lab will save you
4 days in the library every time".

Richard

It really is always Hell, when anyone's Ex was right...

Peter

"Peter Dohm" wrote in message
. ..

(snipped over 100 lines of text)

It really is always Hell, when anyone's Ex was right...

Peter

(For a 2 line reply.)

Peter ......

I encourage you to *please* snip the excess lines from your reply.

Thanks for your consideration,
Rich S.

"Peter Dohm" wrote

I am not sure what material is used in the currently offered commercial
assemblies, but it may very well be glass. (As you might guess, I also
don't know what material to use as a mold for glass--much less how to form
the resulting mold.)

You can make the mold out of about anything that will stand the heat. Wood
has been used, and so has plaster of paris, or even dry sheet rock compound
or concrete. The trick is to line the surface that will be touching the
lexan or plexi with felt, or lacking that, an all cotton material like
t-shirts are made of. The plug needs to be perfect, because any defect in
the plug will transfer onto the plastic lens. Caution, if you go with woven
cloth, some of the weave pattern will come through onto the plastic. Not
good for windshields, but probably OK for light lenses.

When you use lexan, you need to put it in a low temp oven, of around 150 (I
think) for several hours to let all of the water slowly evaporate out of it.
That will prevent the bubbles in the plastic.

The plastic (acrylic or plexi) should be mounted in a frame, and clamped
securely around the edges. When you are ready to mold it, bring the
temperature up rather slowly, until you get a nice amount of sag in the
middle. Then you are ready to pull it down onto the plug.

The plug should be mounted on a base that has a support which is at least
smaller than the outside of the plug, and the support should be on a base
that will not tip over as you begin the process of pulling the plastic down
around the plug. It should be held there until it cools, almost to room
temperature. The excess can then be cut off with an abrasive cut off wheel
on a dremmel tool or die grinder.

If there are rather sharp, deep bends, it may be necessary to smooth the
plastic onto the plug as it is being pulled downward. Wear cotton gloves,
with perhaps a thicker pair of gloves under it to keep from burning your
hand. You will need a helper, unless you came outfitted with more than two
hands. g
--
Jim in NC