It's actually for car headlights that are no longer available. To replace
the internal reflector assemblies with modern ones, as the originals are
plated plastic which fails. But the glass outer cover has a fresnel lens
built in which the modern reflectors don't need. So would it be
economically possible to have copies made of the toughened glass outer but
in plain glass? Or perhaps some other material?

--
*Where do forest rangers go to "get away from it all?"

Dave Plowman London SW
To e-mail, change noise into sound.

Replating the plastic sounds the most viable option. Bring it up on a
classic car forum - it must be a well-solved problem.

In article .com,
wrote:
Replating the plastic sounds the most viable option.

It's not - at least for manageable production runs. They're often of the
order of 10,000 minimum.

Bring it up on a classic car forum - it must be a well-solved problem.

I asked here because it's not easily solved and I'm looking for a viable
work round at a reasonable cost - and there are many here with various
skills and experience - probably more so than on a classic car group, of
which I read several.

--
*He who laughs last has just realised the joke.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article .com,
wrote:
Replating the plastic sounds the most viable option.

It's not - at least for manageable production runs. They're often of the
order of 10,000 minimum.

could you plate it with silver, using the Tollens(?) Reaction? IIRC it's
something like silver nitrate solution and an aldehyde, the silver is
precipitatedout on whatever surface the liquid is in contact with; amateur
telescope makers use it to silver their mirrors (for infra-red mainly, and
when a vapour-deposition chamber isn't available to 'em), and if you could
then coat it with a clear varnish/resin it'd stop the silver tarnishing.

Dave H.
(The engineer formerly known as Homeless)

Dave Plowman (News) wrote:

It's actually for car headlights that are no longer available. To replace
the internal reflector assemblies with modern ones, as the originals are
plated plastic which fails. But the glass outer cover has a fresnel lens
built in which the modern reflectors don't need. So would it be
economically possible to have copies made of the toughened glass outer but
in plain glass? Or perhaps some other material?

Am I right in saying you've got one light assembly thats lost
silvering, and need it fixed? For lights other than headlights the
simplest fix is paint the silvering white, but thats no good for
headlights. Glass can be silver plated glass using electrolysis. Before
people frown, yes it doesnt work like conventional electroplating, but
it does work. Put distilled water in the headlight plastic assy, put
silver electrodes in and pass 9v 1mA between them. Along the way silver
will fall out and plate the container. 1mA gets a small patch of plate
after many hours, so you'll presumably want more current.

There is also self adhesive mirror on a roll, if pushed you could chop
it and apply like a mosaic. Plating much better though! Hopefully
coating the plating thickly with clear varnish will help it stay in
place longer. Adding say 1% of fibre to the varnish should increase
lifetime further without having too much impact on optical clarity.

Redesigning the headlight optics doesnt sound an appealing prospect to
me, and it would look very out of chracter.


NT

Dave Plowman (News) wrote:

It's actually for car headlights that are no longer available. To replace
the internal reflector assemblies with modern ones, as the originals are
plated plastic which fails. But the glass outer cover has a fresnel lens
built in which the modern reflectors don't need. So would it be
economically possible to have copies made of the toughened glass outer but
in plain glass? Or perhaps some other material?

Am I right in saying you've got one light assembly thats lost
silvering, and need it fixed? For lights other than headlights the
simplest fix is paint the silvering white, but thats no good for
headlights. Glass can be silver plated glass using electrolysis. Before
people frown, yes it doesnt work like conventional electroplating, but
it does work. Put distilled water in the headlight plastic assy, put
silver electrodes in and pass 9v 1mA between them. Along the way silver
will fall out and plate the container. 1mA gets a small patch of plate
after many hours, so you'll presumably want more current.

There is also self adhesive mirror on a roll, if pushed you could chop
it and apply like a mosaic. Plating much better though! Hopefully
coating the plating thickly with clear varnish will help it stay in
place longer. Adding say 1% of fibre to the varnish should increase
lifetime further without having too much impact on optical clarity.

Redesigning the headlight optics doesnt sound an appealing prospect to
me, and it would look very out of chracter.

Almost forgot, another option would be paint the plastic with aquadag
or similar, and electroplate conventionally.

Some of these I've tried, some not.


NT

On Mon, 19 Jun 2006 21:17:43 +0100, "Dave Plowman (News)"
wrote:

It's actually for car headlights that are no longer available.

They're not cast, they're pressed. If you can achieve suitable surface
quality and accuracy with slumped glass (gravity presses it under its
own weight) then many hot-glass craft workers should be able to do
one-offs for you. Making the moulds isn't especially hard either. Try
asking in rec,crafts.glass.

In article ,
Andy Dingley wrote:
It's actually for car headlights that are no longer available.

They're not cast, they're pressed. If you can achieve suitable surface
quality and accuracy with slumped glass (gravity presses it under its
own weight) then many hot-glass craft workers should be able to do
one-offs for you. Making the moulds isn't especially hard either. Try
asking in rec,crafts.glass.

Thanks Andy - I'll give that a try.

--
*I yell because I care

Dave Plowman London SW
To e-mail, change noise into sound.