Welcome back. In this lesson we shall cut the crown of our round
brilliant. Run the GemCad program. Press the File Menu key
to get to the File Menu. Now we need to open the project.
Press the Open (O) key to reopen the project. GemCad will
ask you for the name of the project (file). Here, you could type
in the name of the project, but just respond by pressing the Enter
key, and GemCad will activate a file picker. This allows you to
open projects by clicking on their names with the mouse or by
selecting them with the cursor keys. You should see the name of
the current directory printed at the top of your display. You
should see the entry labeled file spec at the top of the
column of files. You should also see the name of your file and
perhaps other GemCad files. If you don't see your file name one
of two things could have happened. If you didn't gave your file
name an extension that doesn't begin with G, the file
will not be matched by the wildcard. If this is the case, click
on file spec and change the wildcard to *.*.
Now, all of the files in the current directory will be visible,
including your project file. If not, you are probably not in the
same directory as you were when you saved the file at the end of
the last lesson. You can navigate through the directory tree by
selecting the directories that end with the backslash \
character. The special directory ..\ is the parent of
the current directory, and clicking on it moves closer to the
root of the directory tree.
So, when you locate your project, move the cursor box around with the mouse or cursor keys to highlight your file name. Then press a mouse button or the Enter key. The stone should look the same as when you saved the project at the end of Lesson 1 as shown in Figure 7.
Now we are ready to cut more facets. Press the >Main Menu key to return to the Main Menu and then press the >Cut Menu key to get to the Cut Facets Menu. We shall now cut our crown mains at index position 64 at an angle of 40°. Press the Index (i) key and enter 0 for the index. Now, enter the angle by pressing the Angle (a) key and entering 40. Now we must enter a point on the facet. In order to see more clearly to position this facet precisely, we can zoom in on the End View. Move the cursor down to the girdle line on the End View. Then press the Zoom (z) key. GemCad will enlarge the End View to fill the entire screen. Move the cursor to where you want the main at index 64 to meet the girdle facets--decide how much girdle to leave by eye. The cursor should be positioned as shown in Figure 8.
Figure 8. Position the cursor to define the girdle thickness
Press the >Point Menu key. Then press the Pt on edge (e) key to pick a point on the facet-to-be. If the cursor snaps to the edge you wanted, enter y to cut the facets. Your display should look like Figure 9.
Figure 9. After cutting the crown mains
The mains meet at a point on the crown. (We're cutting cheap rough with an oversized preform.) We are now ready to enter information about the crown break facets. The cursor should be near the meet point of the crown facet we just cut at index 64 and the girdle facets. Since we want the break facets to meet here also, press the Meet pt (m) key to select this meet point. Enter y to use the point. You should see the message 1pt in the status box.
Now we need to zoom back out to get the big picture. Press the Zoom (z) key. You should now see all four views again as shown in Figure 10. There are only two magnifications--the zoom command toggles between the two.
Figure 10. Zoom out to see the big picture
Now we must decide how large to make the crown break facets. Instead of entering the angle explicitly, we shall let GemCad figure it out. Let's make a construction line to assist us in placing these facets. The minus key (the hyphen or -) is used to draw construction lines. The Constr line (-) command is also found in the Utility Menu. Let's draw a line. Move the cursor away from the stone and press the - key. Move the cursor again and press the - key again. GemCad will draw a dotted line from the first point to the second point. (You can use the Draw (d) command to erase construction lines.) Position the cursor in the Top View near the meet point of the main at 64 and the girdle. To help you position the cursor, you can press the Meet pt (m) key to snap the cursor to the meet point. Enter n (or simply press the Enter key) to discard the point. (Here we are only using the Meet pt (m) key to snap to the meet point quickly.) Press the - key to begin our construction line. Next move the cursor near the meet point of the main facet at index position 16 and press the Meet pt (m) key to snap to the meet point. Press Enter to discard the point. Next, press the - key to draw the construction line. Now move the cursor near the intersection of the construction line and the edge formed by the intersection of the mains at indexes 64 and 8. (The edge will align radially with the 4 index position.) Your cursor should be positioned as shown in Figure 11.
Figure 11. Position the cursor to set size of mains
If we enter a point on the edge at the intersection of the construction lines we will end up with about a 60% table. If you want a smaller table, move towards the center of the crown a bit. When you have the cursor where you want it, press the Pt on edge (e) key to set the point. If the cursor moves only slightly to snap to the edge, enter y to tell GemCad to use the point. You should see the message 2pt at the lower-left-hand corner of your screen. (If it says 1pt then you forgot to enter the meet point of the main at 64 and the girdle facets about four paragraphs back.) Now we need to tell GemCad at what index to cut the facet. Press the >Cut Menu key. Press the Index (i) key and enter “2”; as the index. GemCad should proceed to cut the 16 crown break facets, and your display should look like Figure 12.
Figure 12. Crown mains and breaks
Now we are ready to cut the star facets. Press the >Point Menu key to go to the Point Menu. The cursor should still be at the intersection of the main and break facets along the radius of the stone at the 4 index position. Press the Meet pt (m) key to enter the point and press y to use the point. Now we shall make two more construction lines. We want the line to begin at this meet point, so press the - key to start the construction line. Next move the cursor near the corresponding meet point along the radius at the 52 index position. Press the Meet pt (m) key to snap to the meet point, but press Enter to discard the point. (Again, we are only using the Meet pt (m) key to position the cursor quickly; we don't want our star facet at index 4 to meet here.) Press the - key again to draw the construction line. Now we shall make another construction line. Move the cursor near the meet point of the mains and breaks along the radius at the 60 index position and press the Meet pt (m) key to snap to the meet point, and press Enter to discard the point. Press the - key to start a new construction line. Move the cursor near the corresponding meet point along the radius at the 12 index position, press the Meet pt (m) key to snap to the point, press Enter to discard the point and then press the - key to draw the construction line. The two construction lines should intersect on the main facet at the 64 index position. Move the cursor to this point of intersection. Your display should look like Figure 13.
Figure 13. Establishing the meet point for the star facets
We want the star facets to meet the mains at this point. Press the Pt on facet (f) key to set this point and enter y to use it. This will drop a perpendicular down until it hits the main facet and set the point of intersection of the perpendicular and the facet. You should see the message 2pt at the lower-left-hand corner of your screen. Now we need to tell GemCad to cut the facets at the 4 index position. Press the >Cut Menu key. Then press the Index (i) key and enter 4. Gem will cut the star facets. Redraw the stone by pressing the d key to update the dimension lines. Your display should now look like Figure 14.
Figure 14. After the star facets are cut
Now for the table. Press the Angle (a) key and enter 0 (zero). Press the >Point Menu key. Your cursor should still be at the meet point of the main at 64 and the star facets. Press the Meet pt (m) key. As soon as you enter y GemCad will cut the table. Note that you only had to enter the angle zero and not the index since index has no meaning for angle zero. You should now see the completed brilliant cut on your display as in Figure 15.
Figure 15. The crown is complete
This completes our round brilliant. Note that the only angles we had to enter were 44 for the pavilion mains, 40 for the crown mains, and 90 for the girdle facets. The remaining angles were set by “eye”; by picking points along existing edges or on existing facets. This is often the way you will work when designing a new cut.
This completes Lesson 2, the crown of a round brilliant. Be sure and save the stone: Press >Cut Menu key, the >Main Menu key and then the >File Menu key. Then press the Save (s) key. Since we specified the project name when we opened it, GemCad will not ask you for a file name. GemCad will tell you that the file already exists and ask you if it's O.K. to write over the file. After saving the project, quit the program by pressing the Quit (Q) key.