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astrobeast1
super member

Reged: 09/28/10

Loc: leicester england
sagitta volume calculation
#5717774 - 03/07/13 06:14 AM

Hello to all,
does anyone know of a source for calculating how much glass in volume is taken out from any given mirror blank when forming a sagitta =I am melting my own glass in preformed mould,s and wish to know if possible the weight of glass needed with some degree of accuracy.

many thank,s
Dan

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Mike I. Jones
Post Laureate

Reged: 07/02/06

Loc: Fort Worth TX
Re: sagitta volume calculation [Re: astrobeast1]
#5717780 - 03/07/13 06:26 AM

Volume of a spherical cap = (pi/3)(s^2)(3R-s)

where s = sag, R = radius of curvature

Mike

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astrobeast1
super member

Reged: 09/28/10

Loc: leicester england
Re: sagitta volume calculation [Re: Mike I. Jones]
#5717785 - 03/07/13 06:37 AM

thank,s mike,
appreciate that=very quick !
was wondering if there,s a simpler method like a calculator which only requires an input of the diameter and the planned depth-thank,s

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Mike I. Jones
Post Laureate

Reged: 07/02/06

Loc: Fort Worth TX
Re: sagitta volume calculation [Re: astrobeast1]
#5717792 - 03/07/13 06:47 AM

Let r=D/2, then

V = (pi/6)(s)(3r^2+s^2)

Mike

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astrobeast1
super member

Reged: 09/28/10

Loc: leicester england
Re: sagitta volume calculation [Re: Mike I. Jones]
#5717797 - 03/07/13 06:56 AM

My maths aren't so good as your,s---did you suspect ?

I will see if I can use both calc figures to my benefit. thank,s Dan

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