In this lesson, we will find out how to make a cutting schedule. We will also optimize the angles for quartz.
Open the project to read our brilliant back from disk. Now, change to the Diagram Menu. To list out the cutting schedule, press the List to scrn (l) key. Let's study this for a moment. GemCad will clear your screen and list the schedule. The first line shows the name of the project. The next shows the refractive index. The next shows the total number of facets, with and without the girdles. Next come the symmetry of the stone and the index gear. The next section gives the relative dimensions. The abbreviations refer to the drawing of the stone. Next, comes the facet data. Each tier of facets is shown on a separate line. The angle of the tier (in degrees) is given, and then the index of each facet is given. All facets in a tier are cut at the same angle and cutting depth. Unfortunately there is no way to tell which line goes with which tier. We will remedy this shortly. After you have viewed the listing, press any key to redraw the stone.
Now, let's name (or label) the facets. Move the cursor inside the table in the Top View. Press the Name (n) key. GemCad will highlight the facet ask you for the name of the facet. Enter T for table. GemCad will then redraw the facet and label it with a T. Names can be up to three characters long, but one or two character names make for less clutter. Name all the facets as shown in Figure 16.
Figure 16. After naming all of the facets
Now, press the List to scrn (l) key to list the cutting schedule. Now each line of the facet data begins with the name of the corresponding tier. You can name two facets on a tier with different names, but only one will be printed in the listing.
Now let's analyze the optical performance of our stone. Move the cursor inside the table near the perimeter of the table and press Waytwace (w). GemCad will trace the ray into the stone and back out. (The raytrace command is in the Cut Menu.) Repeat the same for the star and the crown break facets. If your screen becomes too cluttered, redraw with the Draw (d) command. In particular consider the rays shown in Figure 17. On your screen, the portion of the rays inside and outside the stone are shown in different colors. Light entering the stars, mains and breaks leak out the pavilion. Only light entering the table is returned through the crown.
Figure 17. Some light rays
Now let's lower the angles. Move the cursor inside one of the crown mains. Press the Blink facet (b) key (located in the Utility Menu. The angle of the facet will be shown in the box in the upper-left-hand corner of your screen and should be 40°. Now let's scale the crown to make this angle 27°. Make sure the cursor is still inside a crown main and press the Tan ratio (T) key. (This command is in the Cut Menu.) GemCad will tell you what the old angle was and ask you for the new angle. Enter 27. GemCad will immediately rescale the crown.
Next, move the cursor inside a pavilion main and change the pavilion mains from 44° to 42°. The smaller angles are near those recommended by Long & Steele and result in a much better performance for quartz. Now, use the Waytwace (w) command to check the performance. You should see rays similar to Figure 18. All light entering vertically through the mains, and stars now exits through the crown.
Figure 18. Paths of light rays after changing the angles
Execute the Playback (P) command (in the Utility Menu). GemCad will show an animation of the stone. The completed stone should look like Figure 19. You can list a cutting schedule to your printer by moving to the Diagram Menu and pressing the List to file (L) key and entering PRN for the file name. The resulting schedule should look like the listing in Table 1, but the angles might be a bit different since their numerical values were not entered but were set by “eye.”
Figure 19. The completed brilliant
LESSON.GEM
Angles for R.I. = 1.54
57 facets + 16 facets on girdle = 73
8-fold, mirror-image symmetry
64 index
L/W = 1.000 T/W = 0.583 T/L = 0.583
P/W = 0.450 C/W = 0.108 H/W = (P+C)/W+0.02 = 0.578
P/H = 0.778 C/H = 0.187 Vol./W^3 = 0.190
GIRDLE
G 90.00 02-06-10-14-18-22-26-30-
34-38-42-46-50-54-58-62
PAVILION
M 42.00 64-08-16-24-32-40-48-56
B 43.31 02-06-10-14-18-22-26-30-
34-38-42-46-50-54-58-62
CROWN
M 27.00 64-08-16-24-32-40-48-56
B 33.08 02-06-10-14-18-22-26-30-
34-38-42-46-50-54-58-62
S 15.66 04-12-20-28-36-44-52-60
T 0.00 Table
Be sure to save your design with the Save (s) key. This completes the tutorial on the round brilliant.