I want to make a mould for a clear headlamp cover on a sports car.
The body is unpainted (right now) frp, If I could fill the 'socket"
in the front of the car with an expanding foam and work it into shape
after it hardens then I could get a positive, and then vacuum-mould a
bit of acrylic or polycarb to match. The fellow doing the body-work
and painting would like it very much if this did not ruin his nice
work. If there is not a non-sticky foam then what should I use as a
release agent - could be something as simple as parchment papaer I
suppose...

Is there a foam that would suit?

Any other suggestions welcome.

No, these covers are not otherwise available.

jmsiat fired this volley in news:e7a3f467-2d7c-4193-
:

I want to make a mould for a clear headlamp cover on a sports car.
The body is unpainted (right now) frp, If I could fill the 'socket"
in the front of the car with an expanding foam and work it into shape
after it hardens then I could get a positive, and then vacuum-mould a
bit of acrylic or polycarb to match. The fellow doing the body-work
and painting would like it very much if this did not ruin his nice
work. If there is not a non-sticky foam then what should I use as a
release agent - could be something as simple as parchment papaer I
suppose...

Is there a foam that would suit?

Assuming this is not a tight void that would suffer from the foam's
expansion, then line it with the thinnest polyethylene sheeting you can
find -- 1/2-mil "painter's tarp" material comes to mind. It's like dry
cleaners' garment bags.

Even where there are folds to take up the shape, the foam will expand to
compress the film tight against the cavity, and three or four thicknesses
will still take up only a few thousanths.

This is the same method they use to make custom-fit shipping boxes for
delicate instruments. One lines the box with film, applies foam, covers
the foam with another sheet, then "immerses" the object in the ersatz
"water bed" of rising foam. The poly-sheet keeps everything from
sticking to the foam quite effectively, so long as there are no sharp
corners that might poke holes in it.

LLoyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com fired this volley in
. 3.70:

Is there a foam that would suit?



Oh... and, I would use the highest-expansion foam available in order that
fine details will be reproduced. Cap off the whole affair with a final
sheet of poly in order to force the expansion back into the cavity.

Regular "great stuff" will work just fine, so long as you lightly spray
the inside of the (lined) cavity with water just before applying the
film. Great Stuff, being a one-part mix, requires moisture to cure.

LLoyd

I have two points. Generally, your plan will work. As a separation, mold release agent, you can use Saran Wrap (Cling Wrap), but
test it first. My first point is to be certain the foam can be removed mechanically. You will not be able to use just the foam as
a polycarbonate mold, as the temperatures to vacuum form will destroy the foam. ( I think). Second, there are 3 grades of
polycarbonate (lexan), natural, hardfaced on one side and hardfaced on both sides. Be sure you use the latter, or it will scratch
very readily.
Steve

"jmsiat" wrote in message ...
I want to make a mould for a clear headlamp cover on a sports car.
The body is unpainted (right now) frp, If I could fill the 'socket"
in the front of the car with an expanding foam and work it into shape
after it hardens then I could get a positive, and then vacuum-mould a
bit of acrylic or polycarb to match. The fellow doing the body-work
and painting would like it very much if this did not ruin his nice
work. If there is not a non-sticky foam then what should I use as a
release agent - could be something as simple as parchment papaer I
suppose...

Is there a foam that would suit?

Any other suggestions welcome.

No, these covers are not otherwise available.

On Mon, 22 Mar 2010 04:29:13 -0700 (PDT), the infamous jmsiat
scrawled the following:

I want to make a mould for a clear headlamp cover on a sports car.
The body is unpainted (right now) frp, If I could fill the 'socket"
in the front of the car with an expanding foam and work it into shape
after it hardens then I could get a positive, and then vacuum-mould a
bit of acrylic or polycarb to match. The fellow doing the body-work
and painting would like it very much if this did not ruin his nice
work. If there is not a non-sticky foam then what should I use as a
release agent - could be something as simple as parchment papaer I
suppose...

Is there a foam that would suit?

Any other suggestions welcome.

No, these covers are not otherwise available.

We used to foam parts in place in boxes by
1) spray foam in the bottom
2) put a sheet of poly on top
3) put the manpack radio on that
4) put down another layer of poly
5)spray foam on that
6)close the box.
It filled the spaces and left few voids.

Couldn't you put poly in the socket, add foam, cover, remove it from
the socket, fill voids, and cast from the result?

--
If we attend continually and promptly to the little that we can do, we
shall ere long be surprised to find how little remains that we cannot do.
-- Samuel Butler

On Mon, 22 Mar 2010 06:43:51 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:



Assuming this is not a tight void that would suffer from the foam's
expansion, then line it with the thinnest polyethylene sheeting you can
find -- 1/2-mil "painter's tarp" material comes to mind. It's like dry
cleaners' garment bags.

Even where there are folds to take up the shape, the foam will expand to
compress the film tight against the cavity, and three or four thicknesses
will still take up only a few thousanths.

This is the same method they use to make custom-fit shipping boxes for
delicate instruments. One lines the box with film, applies foam, covers
the foam with another sheet, then "immerses" the object in the ersatz
"water bed" of rising foam. The poly-sheet keeps everything from
sticking to the foam quite effectively, so long as there are no sharp
corners that might poke holes in it.

LLoyd

I bought some parts on eBay last month. The seller tried to use this
method of packing.

Short story, the Great Stuff melted the bag. A week of cutting and
scraping with a serrated knife finally freed my parts.

Test your bag.

On Mon, 22 Mar 2010 04:29:13 -0700 (PDT), jmsiat
wrote:

I want to make a mould for a clear headlamp cover on a sports car.
The body is unpainted (right now) frp, If I could fill the 'socket"
in the front of the car with an expanding foam and work it into shape
after it hardens then I could get a positive, and then vacuum-mould a
bit of acrylic or polycarb to match. The fellow doing the body-work
and painting would like it very much if this did not ruin his nice
work. If there is not a non-sticky foam then what should I use as a
release agent - could be something as simple as parchment papaer I
suppose...

Is there a foam that would suit?

Any other suggestions welcome.

No, these covers are not otherwise available.

Go to a hobby shop and look for "Mountains in Minutes".
http://www.hobbymasters.com/islemoun...dscapekit.aspx

Model railroad buffs use it. It's a two-part foam that is a lot less
sticky than one-parts like Great Stuff, and it expands more. I'd use
PAM as a release agent on the car if you'll want to paint later,
because silicone release agents can be diffult to remove completely
and they do play hell with paint. PAM is basically lecithin, easily
removed with detergent.

Once the foam cures, it's non-sticky and easily shaped with sandpaper
or hot element (hot wire or soldering iron) though hot seriously
stinks so have good ventilation.

This stuff is also pretty good insulation. I measured the thermal
conductivity once, don't recall now but it was quite low.

Larry Jaques wrote:
On Mon, 22 Mar 2010 04:29:13 -0700 (PDT), the infamous jmsiat
scrawled the following:

I want to make a mould for a clear headlamp cover on a sports car.
The body is unpainted (right now) frp, If I could fill the 'socket"
in the front of the car with an expanding foam and work it into shape
after it hardens then I could get a positive, and then vacuum-mould a
bit of acrylic or polycarb to match. The fellow doing the body-work
and painting would like it very much if this did not ruin his nice
work. If there is not a non-sticky foam then what should I use as a
release agent - could be something as simple as parchment papaer I
suppose...

Is there a foam that would suit?

Any other suggestions welcome.

No, these covers are not otherwise available.

We used to foam parts in place in boxes by
1) spray foam in the bottom
2) put a sheet of poly on top
3) put the manpack radio on that
4) put down another layer of poly
5)spray foam on that
6)close the box.
It filled the spaces and left few voids.

Couldn't you put poly in the socket, add foam, cover, remove it from
the socket, fill voids, and cast from the result?


Actually, a little more clearance is needed.

So, make a plug, slightly larger than the manpack radio...

Because this stuff has NO sense of humor.

--

Richard Lamb
http://www.home.earthlink.net/~cavelamb/

Don Foreman wrote:
On Mon, 22 Mar 2010 04:29:13 -0700 (PDT), jmsiat
wrote:

I want to make a mould for a clear headlamp cover on a sports car.
The body is unpainted (right now) frp, If I could fill the 'socket"
in the front of the car with an expanding foam and work it into shape
after it hardens then I could get a positive, and then vacuum-mould a
bit of acrylic or polycarb to match. The fellow doing the body-work
and painting would like it very much if this did not ruin his nice
work. If there is not a non-sticky foam then what should I use as a
release agent - could be something as simple as parchment papaer I
suppose...

Is there a foam that would suit?

Any other suggestions welcome.

No, these covers are not otherwise available.

Go to a hobby shop and look for "Mountains in Minutes".
http://www.hobbymasters.com/islemoun...dscapekit.aspx

Model railroad buffs use it. It's a two-part foam that is a lot less
sticky than one-parts like Great Stuff, and it expands more. I'd use
PAM as a release agent on the car if you'll want to paint later,
because silicone release agents can be diffult to remove completely
and they do play hell with paint. PAM is basically lecithin, easily
removed with detergent.

Once the foam cures, it's non-sticky and easily shaped with sandpaper
or hot element (hot wire or soldering iron) though hot seriously
stinks so have good ventilation.

This stuff is also pretty good insulation. I measured the thermal
conductivity once, don't recall now but it was quite low.

HIGHLY recommended for Ice Box insulation on sail boats.



--

Richard Lamb
http://www.home.earthlink.net/~cavelamb/

fired this volley in
:

Short story, the Great Stuff melted the bag

Then it wasn't polyethylene, or he used a hot-mix dispenser.

Polyurethane neither deteriorates nor sticks to polyethylene.

LLoyd