Re: [ATM] Vacuuming a Foil

["Malcolm Macdonald" <toliman@wave.co.nz>]

----- Original Message ----- 
From: "Treur, Harro" <H.Treur@wlb.amsterdam.nl>
To: <atm@atmlist.net>; <info@everest-coatings.nl>
Sent: Thursday, September 30, 2004 9:06 PM
Subject: [ATM] Vacuuming a Foil


> Hello,
>
> Yesterday-evening my neighbour and I had been discussing possibilities of
> spincast mirrors.
> Two hours later Robert ran into my home calling that he found the answer!!
> Why not span a thin reflective foil over the rim of a basket and then put
a
> slight vacuum beneath. This would create a paraboloic shape.
> This idea sounded familiar to me. Maybe I have read it once on the
> ATM-pages.

Yes, I too remember this discussion a few years ago. I seem to remember that
they had some succes but the main problem was the the connection between the
ring and the mylar. It would not stretch evenly enough over the entire
surface, and getting the exact same tention all the way arround was a
problem.

There was no spinning involved, just the light vacume at the back.

 >But in my opinion the problem is keeping the surface in shape,
> because I guess the surface is extremely dependent on the amount of
> air-pressure and temperature.

More important I think, is the evenness or consistancy of the material. But
a good few years on now there may be better quality materials on the market.

> While brainstorming we considerded building in a simple active
shape-control
> mechanism: a laserlight which reflects its light on the surface and ends
up
> on a photocell. As soon as pressure differences occur, the cell will
notice
> and will correct the amount of "vacuum".
> I think enough vacuum can be obtained by attaching an injection-tube to
the
> "Vacuumchamber".
> Pulling the tube somewhat outside will deliver the requiered
> amount of lower pressure.
> As soon as the photocell notices that a bit more vacuum is needed, the
> injection-tube is pulled outside by a motor until he correction is
> sufficient.
>
> Questions:
> 1 - How is your feeling about my neighbour's idea ?

Ans.  Give it a try. It may work and if it doesn't you have lost nothing.

> 2 - I would like to start some experimenting. Can anybody give a
suggestion
> what kind of foil could be used ? (a bit stretcable, good reflection, very
> little surface rougness).

I would suggest a silver 'Survival Blanket'  to practice on first. They are
cheep and there is enough meylar for a lot of mistakes.

Good luck   and keep us informed.

           Malcolm.

PS I seem to remember some advice.  Don't stretch the Meylar too tight. Just
enough to make it flat.

> Harro Treur
>
> Met vriendelijke groet
>
> Harro Treur
> Waterleidingbedrijf Amsterdam
> 020 - 5536 830
>
>
> _________________________________________________________________
>
> De informatie verzonden in dit e-mailbericht is vertrouwelijk en
uitsluitend bestemd voor de geadresseerde. Openbaarmaking,
vermenigvuldiging, verspreiding en/of verstrekking van deze informatie aan
derden is, behoudens voorafgaande schriftelijke toestemming van
Waterleidingbedrijf Amsterdam, niet toegestaan.
> Waterleidingbedrijf Amsterdam staat niet in voor de juiste en volledige
overbrenging van de inhoud van een verzonden e-mailbericht, noch voor
tijdige ontvangst daarvan.
>
> _________________________________________________________________
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.770 / Virus Database: 517 - Release Date: 28/09/2004

_______________________________________________
ATM mailing list http://www.atmlist.net/