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Re: [ATM] Thermal Mass - WAS Tees instead of triangles
Hi Cary, i feel i have to reply to this ;-)
As far as i know i am the sole maker of the plates and posts type of
mirror blanks, and i agree with all you say,
from actual experience using them.
As an example here is a foucault image of my latest 25" f/4 post and
plates mirror :
http://www.cablevision.qc.ca/astro/25F4parabola.jpg
the mirror is supported only by a center hole in the backplate.
here is another image when it was close to a sphere, same center
only support :
http://www.cablevision.qc.ca/astro/25ins_fev05_foucault.jpg
indeed, the mirror is very rigid, and does cool down very quickly.
> Now the catch!!! No one is commercially producing cellular mirror blanks -
> yet....
>
i can make them, they work extremely well, but so far i have been unable to
interest
anybody !
Human nature issue maybe ?
Jean-Guy Moreau
----- Original Message -----
From: "Cary Chleborad" <Cary@Chleborads.com>
To: <atm@atmlist.net>
Sent: Saturday, May 21, 2005 2:28 AM
Subject: [ATM] Thermal Mass - WAS Tees instead of triangles
>
> This topic has drifted along to thermal issues and I thought it would be
> appropriate to follow on with this.
>
> Now that people are considering the scale of thermal differentials between
> the optic and the ambient air and even seeking active cooling solutions -
> what about cellular structured mirror blanks?
>
> There have been a couple of folks in recent years that have been fusing post
> and plate structure systems together. The advantage of such as system is
> one can achieve the cross section of a very thick mirror blank at only ~1/3
> the mass of an equally thick solid blank.
>
> The interesting thing about such a blank is that the amount of heat is
> directly proportional to the mass of the blank. On this basic principle
> alone a cellular mirror with 1/3 the mass of a traditional mirror will
> thermally equalize three times faster.
>
> Now, it gets better! Heat flows out of a structure at a rate proportional
> to the thickness of the material it is flowing from. The cellular structure
> ends up having web thicknesses as much as 1/16 the thickness of a
> traditional blank. The heat can now escape the blank at a rate insanely
> faster than our poor old plano solid blanks.
>
> To recap, 1/3 the mass = 1/3 the heat. Which can escape the blank 4, 8, 16
> times faster than traditional blanks. You end up seeing thermal
> equalization rates that take minutes instead of hours and with no fans.
>
> Now, to top it off and make it sound like an infomercial:
>
> It still gets better!!! A cellular blank is not only less massive and cools
> much faster; it ends up being much stiffer than and equally thick and solid
> blank. Furthermore if the cellular blank is made by a full casting instead
> of fusing plates and posts the cellular structure can be designed to be
> totally self supporting. The mirror then sits right on the collimation
> bolts!! No more fussing with complex mirror cell designs!!
>
> Now the catch!!! No one is commercially producing cellular mirror blanks -
> yet....
>
>
> -Cary
>
>> > > I'm using this idea to address the thermal problem:
>> > >
>> > > http://www.balinka.com/portfan.htm
>> >
>> > You should really consider a front blowing fan. With the 3 inch thick
>> > mirror, getting the air moving on both sides is going to help a lot.
>> > Also, perhaps even more important, a rear fan doesn't break up the
>> > thermal boundary layer on the front side that causes much of the image
>> > distortion.
>> >
>> >
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>
----- Original Message -----
From: "Cary Chleborad" <Cary@Chleborads.com>
To: <atm@atmlist.net>
Sent: Saturday, May 21, 2005 2:28 AM
Subject: [ATM] Thermal Mass - WAS Tees instead of triangles
>
> This topic has drifted along to thermal issues and I thought it would be
> appropriate to follow on with this.
>
> Now that people are considering the scale of thermal differentials between
> the optic and the ambient air and even seeking active cooling solutions -
> what about cellular structured mirror blanks?
>
> There have been a couple of folks in recent years that have been fusing post
> and plate structure systems together. The advantage of such as system is
> one can achieve the cross section of a very thick mirror blank at only ~1/3
> the mass of an equally thick solid blank.
>
> The interesting thing about such a blank is that the amount of heat is
> directly proportional to the mass of the blank. On this basic principle
> alone a cellular mirror with 1/3 the mass of a traditional mirror will
> thermally equalize three times faster.
>
> Now, it gets better! Heat flows out of a structure at a rate proportional
> to the thickness of the material it is flowing from. The cellular structure
> ends up having web thicknesses as much as 1/16 the thickness of a
> traditional blank. The heat can now escape the blank at a rate insanely
> faster than our poor old plano solid blanks.
>
> To recap, 1/3 the mass = 1/3 the heat. Which can escape the blank 4, 8, 16
> times faster than traditional blanks. You end up seeing thermal
> equalization rates that take minutes instead of hours and with no fans.
>
> Now, to top it off and make it sound like an infomercial:
>
> It still gets better!!! A cellular blank is not only less massive and cools
> much faster; it ends up being much stiffer than and equally thick and solid
> blank. Furthermore if the cellular blank is made by a full casting instead
> of fusing plates and posts the cellular structure can be designed to be
> totally self supporting. The mirror then sits right on the collimation
> bolts!! No more fussing with complex mirror cell designs!!
>
> Now the catch!!! No one is commercially producing cellular mirror blanks -
> yet....
>
>
> -Cary
>
>> > > I'm using this idea to address the thermal problem:
>> > >
>> > > http://www.balinka.com/portfan.htm
>> >
>> > You should really consider a front blowing fan. With the 3 inch thick
>> > mirror, getting the air moving on both sides is going to help a lot.
>> > Also, perhaps even more important, a rear fan doesn't break up the
>> > thermal boundary layer on the front side that causes much of the image
>> > distortion.
>> >
>> >
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>
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