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home made 80 mm shell

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Hi guys! I have made my hemispherical paper shell with a mould! they are 80mm EXTERNAL DIAM.(made with 10 layers of kraft paper) how many layers of pasting are necessary to complete the shell? and what internal DIAMETR. of mortar can i use? thz!!
sorry for my bad english ^_^

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I'd say 5-6 with a good booster (more than usual).
And what about a mortar that fits the size of the shell? (after pasting)
Maby 4" cuz 3" is too small

Edited by 00h

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thx! Because I read on pyroGuide that for the 3'' shell are required 13 layers( posted charts)
Mortar size (inches): Actual Shell Size (inches): Paper weight: Number of wraps: Size of paper strips:

3" 2-5/8" 30-40lb 13 3/4" wide x 4" long
4" 3-3/4" 50-70lb 9 1" wide x 5-1/2" long
5" 4-5/8" 60-70lb 10 1" wide x 7" long
6" 5-9/16" 60-70lb 12 1.5" wide x 8-1/2" long
8" 7-1/2" 70lb 14 1.5" wide x 11-1/2" long

What do you think about it? is correct?
For the size of mortar i don't know because i used 8.5cm inside diam. with 1 layers but the break is ugly and asymmetric.. I have supposed 9 cm internal diam..
What metod is the best to use for pasting?

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I use gom tape, and as a booster for 3 inch shells 3 grams flash.
And just paste around the shell side to side all around.
Cuz of the big-ass booster you don't need a lot of pasting.

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No problem ^_^ but remember testing is the best way to find out if something works.( unless it involves safety)

Edited by 00h

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okkk!! I saw on pyroGuide how to make 3'' shell but i don't undestand the formula y=x+3/pi ( what is pi?) and why he use 3 strip pasting metod that correspond to multiply for 2 the layers to find effective layers? can you explain me this? ....another answer.... sorry ^_^ can I replace red gum with shellac in colored composition without problem?






link:
http://www.pyroguide.com/index.php?title=C...hell_%283%22%29


this is the text from pyroguide:
This shell needed 10 layers of pasting (=20 effective layers) to complete. The diameter of the finished shell should be y=x*3/pi, where y is the diameter of the finished shell and x is the size of the mortar. So for this shell it should be 3*3/pi=2,86". Making it this diameter might take a lot of time for beginners, however it is not as problematic with small shells like this one. Making shells like the size of 6" or bigger will take a lot more of work. After the layers of pasting, let the shell dry completely.

Edited by only connect

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Never heard of Wikipedia?

π (sometimes written pi) is a mathematical constant whose value is the ratio of any circle's circumference to its diameter in Euclidean space; this is the same value as the ratio of a circle's area to the square of its radius. The symbol π was first proposed by the Welsh mathematician William Jones in 1706. It is approximately equal to 3.14159 in the usual decimal notation (see the table for its representation in some other bases). π is one of the most important mathematical and physical constants: many formulae from mathematics, science, and engineering involve π.[5]

π is an irrational number, which means that its value cannot be expressed exactly as a fraction m/n, where m and n are integers. Consequently, its decimal representation never ends or repeats. It is also a transcendental number, which implies, among other things, that no finite sequence of algebraic operations on integers (powers, roots, sums, etc.) can be equal to its value; proving this was a late achievement in mathematical history and a significant result of 19th century German mathematics. Throughout the history of mathematics, there has been much effort to determine π more accurately and to understand its nature; fascination with the number has even carried over into non-mathematical culture.

The Greek letter π, often spelled out pi in text, was adopted for the number from the Greek word for perimeter "περίμετρος", first by William Jones in 1707, and popularized by Leonhard Euler in 1737.[6]

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On pyroguide stays 3*3/pi and not 3^3/pi :(

ooo stupid error.... ^_^ I have another question.. the last one :P what is the external diametr. for a 4'' and 3'' shell bought without any pasting?

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