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# sagitta volume calculation

4 replies to this topic

### #1 astrobeast1

astrobeast1

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Posted 07 March 2013 - 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

### #2 Mike I. Jones

Mike I. Jones

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Posted 07 March 2013 - 06:26 AM

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

where s = sag, R = radius of curvature

Mike

### #3 astrobeast1

astrobeast1

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Posted 07 March 2013 - 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

### #4 Mike I. Jones

Mike I. Jones

Gemini

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Posted 07 March 2013 - 06:47 AM

Let r=D/2, then

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

Mike

### #5 astrobeast1

astrobeast1

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Posted 07 March 2013 - 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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