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Shell Building Charts (Round Shells)Edit

From PyroGuideEdit

This page tries to give answers to questions everyone trying to make a successfull round shell sooner or later will have to ask. Keeping in mind the desired shell diameter such questions are e.g.: "How thick should my hemispheres be?", "How many layers are desirable for pasting the shell?", "How much grain will it take to lift my shell?", "What size stars for which shell size?" etc.

It is plain that one could work out the optimum data for each shell himself, but this would mean having to face a process of trial and error consuming both time and material. As pertinent data is available, this would mean to reinvent the wheel.

Round shells are notoriously more labour-intensive than their counterpart cylindrical shells. Nevertheless, some of the data needed to construct these intricate shells will be listed here.  Table 1  Using the 3-strip pasting method, this chart gives information on the dimensions and amounts of paper needed to wrap shells. Note that these are approximations. Depending on the shells you buy/make, and the mortars you use, this information could change.

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

Table 2  This table shows the size of various types of stars needed for each size shell and the approximate amount of each to complete the shell. Note that these are only approximations, as star tooling sizes will vary.

Shell size (inches): Size of Pumped Star: Size of Cut Star: # Pressed Stars: # Cut Stars:
3" 1/4" - 3/8" 1/4" ~110 ~100
4" 3/8" - 1/2" 1/2" ~130 ~120
5" 1/2" - 5/8" 1/2" ~150 ~140
6" 5/8" - 3/4" 3/4" ~160 ~140
8" 3/4" - 1" 7/8" ~160 ~150

Table 3  Typical round shell burst heights, mortar lengths and minimum safe display radius.

Shell size (inches): Burst Height (ft.) Burst Height (m) Mortar Length (single break) Radius in ft (m)
3" 400 120 15 in. 210 (65)
4" 500 150 20 in. 280 (85)
5" 600 180 24 in. 350 (105)
6" 700 210 28 in. 420 (125)
8" 900 270 34 in. 640 (190)

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