Figuring materials

[Cjs]

Wondering how to figure out my material list for a 34" casted dome, 3" thick cast of homebrew with ss needles.

[david s]

Use volume of a sphere = 4/3 x Pi x r3
calculate volume of sphere using outside diam (ie r = 20")
Deduct vol of inner sphere using r = 17"
Then halve the result because it's a hemisphere.

Add 2% of the dry weight of castable of stainless steel needles.
Also add around 2 grams of fine polypropylene fibres for every 10 litres (a bucketful) of castable

[AndrewT]

Maybe this (in metric):

diam radius volume
outer 1.02m .51 0.56
inner 0.86m .43 0.33
----
difference (shell volume) 0.230

divide by 2 (hemisphere) 0.115

times 2000 (kg/m3 required of castable) = 230kg of castable = 9.2 x 25kg bags.


Hopefully I didn't stuff it up.

[david s]

That sounds about right. The extra required for the entry equals approximately the same volume taken up by the oven mouth.