question about marble size & how much rod it would take....

[istandalone24/7]

ok i've got an important question...i need to make a 8cm (3.15") marble, and can someone point me in the right direction for how much 30mm rod it would take to get there?
i swear that i've seen a calculator somewhere for this exact purpose, how much X sized rod does it take to make an X sized sphere.
can someone point me in the right direction? i appreciate any help and/or advice in this matter.

have a good day everyone, and flame on.

[Jackass Glass]

the volume of the marble would be 22.457924999999996 cubic inches. http://www.calculatoredge.com/enggcalc/volume.html#cylinder

If i used this correctly: http://www.onlineconversion.com/object_volume_cylinder_tank.htm

and input 22.457924999999996 for volume and 1.33 inches (33 MM )for the radius

you get a length of 16.16 inches. which i dont think is correct just in my head lol. anyway the tools are there...

[Sparko]

Hrmm, no but this is fun to think about, its like a word problem from school i actually want to try to do. I suck at math but.... "maybe", now look everyone i said maybe so dont kill the messenger but....What if you took a 1 inch piece and made a marble of it and saw how big it was...Then once you measure the diameter (id use my digi calipers), you could use that number to figure out how much you would need to make one thats 3.15''. Just a thought.

[istandalone24/7]

they guys on FB group "glassblowing tips from dicks" came up with about 15" of 30mm rod. which is what i ended up using, roughly. that was the lens alone, add the section with the silver shavings and opal, than backed in cobalt with some wrapped and raked striking colors i should be just about 3.15" exactly.

thanks everyone.

[aommaster]

If, by any chance, you'd like to do this calculation again, you can use the following equation to get the length of glass needed to make a sphere of a given diameter:

l = 2/3 x (dm)3 x (1/dr)2

where:
l is the length of rod you need
dm is the diameter of the marble you're making
dr is the diameter of the rod you're using to make said marble

Only thing to watch out for is that you use the same units all the way throughout.