Designed by Bob Keller 12.03.01 Bob Keller
Angles for R.I. = 1.54 and up 64 facets + 7 facets on girdle = 71 1-fold mirror-image symmetry (Pseudo 7-fold) 96 index L/W = 1.011 T/W = 0.397 T/L = 0.393 P/W = 0.411 C/W = 0.219 H/W = (P+C)/W+0.02 = 0.650 P/H = 0.633 C/H = 0.336 Vol./W^3 = Vol./W^3 = 0.215 Brightness at 0° tilt for RI = 1.54 COS = 77.3 ISO = 92.9
Brightness at 0° tilt for RI = 1.76 COS = 73.6 ISO = 92.1
Pavilion 1 41.00 96-14-27-41-55-69-82 Cut to culet centerpoint g1 90.00 96-14-27-41-55-69-82 Match 1, set size and establish girdle Crown a 50.00 96-14-27-41-55-69-82 Match g1, level upper girdle line b 38.78 04-10-31-37-45-51-59-65-86-92 Meet a.g1.g1.a b' 39.59 18-23-73-78 Meet a.g1.g1.a c 33.52 04-10-18-23-31-37-45-51-59-65-73-78-86-92 Meet b.a.b d 27.34 04-10-31-37-45-51-59-65-86-92 Match c d' 26.87 18-23-73-78 Match c e 21.76 96-14-27-41-55-69-82 Meet d.c.c.d t 0.00 Table Meet e.d.d.e
Seventh Heaven Cutting Notes
The Seventh Heaven Design File is available for GemCad users. At right is a photorealistic raytrace model of Seventh Heaven rendered for RI = 1.76 using GemCalc.
Seventh Heaven is a bright heptagon (7-sided) shape cut for materials of medium to heavy color saturation. Cutting a true or "regular" heptagon as a girdle outline (all edge lengths and angles equal) to Platonic perfection without resorting to fractional indexes requires the use of an index gear that is whole number divisible by 7, such as a 56 tooth gear (7x8). Many faceters do not have a perfect "hepta" gear for their machines, but 96 tooth gears are commonly owned and they close to whole number divisible by 7 (96/7 = 13.77). By rounding off a tooth here and there (14+13+14+14+14+13+14 = 96), it is possible to approximate the shape of a regular heptagon with a 96 gear so closely as to be practically indistinguishable in appearance.
Seventh Heaven employs what could be termed "Pseudo 7-fold" symmetry. It can be cut for the most part using the 96 gear as if it had true 7-fold symmetry. But cut that way all around there are eight facets on the crown which will not quite meet up properly if cut using the same angle and depth as the rest of the facets in the b and d courses. These are the b' facets (18-23-73-78) and the d' facets (18-23-73-78), which must be cut at slightly different angles than the others in their courses to meet precisely all around. When this is done as detailed in the cutting instructions, the design symmetry is actually 1-fold.
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© Bob's Rock Shop Bob Keller