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To run GemCad, type GEMCAD at the DOS prompt. GemCad will print its version number and copyright notice. After you press any key or mouse button to acknowledge the message, GemCad will switch your display to the graphics mode. Your display should then look something like Figure 1.
Figure 1. Display when GemCad is first run
This is an actual screen dump with a VGA display. In EGA and VGA modes, GemCad displays white lines on a blue background. These have been reversed for ease of printing. (An EGA display will look slightly less resolved vertically, and a CGA will look considerably less resolved vertically.) The screen is divided into four views, similar to an engineering drawing. The Top View is at the upper-left, the Side View is at the upper-right, the End View is at the lower-left, and the Bottom View is at the lower-right. The index gear is indicated by a circle of numbers in the Top View. When GemCad is first run, a 64-tooth index gear is used. The index positions start at 64 at the bottom of the Top View and increase counterclockwise. This rather peculiar orientation was chosen to keep facets cut at small index numbers visible in the Top, Side, and End Views simultaneously. This will make better sense as we cut our first stone. (You can make the I.D. position be at the top if you want. See the Index gear (g) key in the reference section at the back of this manual.))
While working through this tutorial, be careful not to press the standard alphabetic keys unless responding to questions that GemCad asks. Most of the alphabetic keys are shortcuts for commands that we shall learn to execute with the function keys. Caps Lock should also be turned off (the light should not be lit) since there are more commands than letters, and commands performed by pressing capital letters are generally more dangerous than commands performed with lower-case letters.
What better way to learn than by doing! Let's begin with a standard round brilliant in quartz. We will use 44° for the pavilion mains and 40° for the crown mains. A round brilliant has eight-fold, mirror-image symmetry and can be cut on a 64 index gear. These are the default settings when GemCad is first run. (You can change the symmetry with the Symmetry (y) command described in the reference section of this manual.) We shall begin by cutting girdle facets at 90° to preform the stone. At the left of your display you will notice the title “MAIN MENU” and several lines beginning with F1-F6 that correspond to the function keys on your keyboard. The function keys will be along the left or top of your keyboard depending on the model. In the Main Menu, all of the labels begin with the > character indicating that selecting the corresponding function key will move to a different menu. Now, experiment with moving around in the menu structure by pressing the function keys corresponding to labels starting with > If you are using a mouse, you can also point at one of the function key legends to cause it to “light up.” Then press any mouse button to execute the highlighted choice.
You will notice single alphabetic characters to the right of function key labels. These are abbreviations for the corresponding function key commands. Typing the alphabetic key is equivalent to pressing the corresponding function key. So what's the shortcut if either takes but a single keystroke? The advantage is that you don't have to be in any particular menu to execute a command with an alphabetic key. This saves you the trouble of wandering through the menu hierarchy if you already know the commands since all the commands are available all the time. If you type reasonably well, the alphabetic keys might be easier to locate than the function keys. Remember to be sure that CAPS LOCK is off (the light is not lit) since upper-case commands are different from (and generally more dangerous than) lower-case commands.
The help key is F11 (or Shift-F1) in every menu. If you press the Help (h) key followed by another function key, GemCad will print a one-sentence description of what the key does. This tells what the key does when it is not preceded by the Help (h) key. You should have received a sheet of paper listing all of the menus. (A file called MENUS.TXT contains the same information.) Use this for a road map as you explore the menus. After you have explored the menus, get back to the Main Menu by pressing the >Main Menu function key.
Figure 2. Girdle facets
Cutting is done while in the menu called Cut Facets Menu. To get to the Cut Facets Menu from the Main Menu, press the >Cut Menu key. We shall begin by cutting 16 girdle facets at 90° to preform the stone. (GemCad can handle only faceted or knife-edge girdles--it cannot handle a round girdle.) Using a 64 index, the girdle facets are at indexes 2, 6, 10.... To tell GemCad to cut at index position 2, use the Index (i) key. You will see the question, “Index?” appear at the top of your screen in dark letters on a white background. Enter 2. (That is, press the 2 key and then press the key labeled Enter.) You can correct mistakes with the Backspace key any time before pressing Enter. Any time GemCad needs a response from you, it will prompt you at the top of the screen. After you enter the 2, you will notice the message i2.0 in the status box at the lower-left-hand corner of your screen. This portion of the screen contains information about facets about to be cut.
Now we need to tell GemCad at what angle to cut the facet. To do this, press the Angle (a) key. GemCad will ask “Angle?” at the top of the screen. Enter 90. (Press the 9 key, the 0 key and then the Enter key.) You might notice the message a90.00,i2.0 appear briefly in the status box at the lower-left-hand corner of your screen while GemCad cuts the sixteen girdle facets! Your screen should look like Figure 2. GemCad knows to cut sixteen facets because it is set for eight-fold, mirror-image symmetry. (These are the default settings, but they may be changed easily.) GemCad will cut a facet or course of facets as soon as you have given it enough information. In this case, we specified the index, angle. For the other facets we will cut later, we will also have to specify a cutting depth, but for this first tier of facets, a reasonable cutting depth is assumed. The fundamental rule of GemCad is that it cuts a set of facets as soon as you give it enough information to completely specify one of the facets.
The four views of the stone are projections of the stone onto the faces of a cube. The advantage of cutting facets in the Top View is that the x coordinate is shared with the End View and the y coordinate is shared with the Side View. Neither axis of the Bottom View aligns with any of the other views.
A word about correcting errors in entry: Entering two different indexes will cause the first index to be discarded. If you make a mistake entering the index, simply enter it again. If GemCad has just cut a facet that didn't come out as you hoped, you can use the Undo (u) key found in several of the menus. This will undo the previous command that changed the stone. The Undo (u) command only undoes the last change to the stone. The undo command will not undo itself. If GemCad is busy cutting off facets or otherwise taking longer to do something than you might expect, press the Esc key to interrupt. This will automatically perform an undo.
Now back to our brilliant. We shall cut the pavilion mains next. We need to indicate to GemCad at what depth to cut the mains. You specify the cutting depth of a facet to GemCad by entering one or more points on the facet-to-be. You specify points to GemCad by moving the cursor around on the screen and by making choices in the Point Menu with the function keys. Now go to the Point Menu by pressing the >Point Menu key.
The cursor is located at the intersection of cross-hairs on the screen that look like a + sign. To move the cursor around on the screen, you can use either the arrow keys on the calculator-style numeric keypad or the cursor keys (if your keyboard has them). The odd numerals 1, 3, 9, and 7 on the numeric keypad make the cursor move diagonally. If the numeric keys on your keyboard are the same keys as the cursor keys, it doesn't matter whether or not the Num Lock key is active. Now experiment with moving the cursor around. The cursor accelerates if held down--that is, the step size increases the longer you hold down a key. GemCad can also make use of a Microsoft or compatible mouse (most are). If your mouse doesn't do anything, its probably because you have not loaded the driver software supplied with your mouse. See the section on mice at the end of the reference section of this manual.
Move the cursor down to near the center of the End View. If you press the space bar, GemCad will draw a pair of dotted lines across the screen intersecting at the cursor. This allows you to line up things in different views. Move the cursor so that it aligns horizontally with the dot at the center of the Bottom View and so that it aligns with the vertical edge of the girdle facet at the center the End View. (Pressing the space bar again will remove the previous cross-hairs.) When the cursor is in the End View, it specifies the x and z coordinates. When it is aligned horizontally with the dot at the center of the Bottom View, the z coordinate is zero. Your cursor should be positioned as in Figure 3.
Figure 3. Positioning the cursor to pick the girdle line
Press the Pt on edge (e) key. This causes GemCad to look in the view containing the cursor is for the edge nearest the cursor. The cursor does not have to be exactly on the edge; it will “snap” to the nearest edge. If the (x, y, z) coordinates GemCad prints are close to (0.0, 1.0, 0.0), enter y in response to the question about whether to use the point. GemCad will ask you this question whenever you enter a point with any of the commands in the Point Menu. You should see the message 1pt in the status box at the lower-left-hand corner of your screen.
What if you enter y to use a point when you didn't mean to? If you redraw the stone with the Draw (d) key in the Cut Facets Menu or Point Menu, all points, the angle, and the index will be discarded. The status box will display the total number of facets.
Now we can tell GemCad at what index to cut the mains. Press the >Cut Menu key. Next, press the Index (i) function key. Enter 0. (Index position 0 is the same as index position 64.) You should see the message 1pt,i0.0 in the status box. Now press the Angle (a) key and enter the pavilion main angle 44. GemCad will then proceed to cut the eight main facets. Redraw the stone with the Draw (d) key. Your screen should look like Figure 4. The Draw (d) command updates the dimension lines. The List to scrn (l) command gives the numerical values of various ratios of the dimensions indicated by the abbreviations.
Figure 4. After cutting the pavilion mains
Now, you might be wondering what the bottom of our stone is doing in the Top View. Not to worry: we will transfer the stone later. Generally, you will find it easiest to cut facets on the Top View. You might also be wondering how GemCad knew to cut only eight main facets but sixteen girdle facets. Since we are using mirror-image symmetry, index position 64 (or 0) is mirrored by itself. The same is true for the star facets which we will cut at index position 4, 12, 20....
Now we will cut the pavilion break facets. Instead of telling GemCad at what angle to cut the breaks, we will tell GemCad where to cut the facet and have it figure out the angle. The cursor should still be near the meet point of the main facet at the 64 index and the girdles in the End View. (You don't have to be right on the meet point, just near it.) Press the key labeled >Point Menu. Now press the Meet pt (m) key. The cursor should “snap” to the nearest meet point and ask you whether to use the point. Answer with a y if GemCad has found the meet point of the girdles and the main at index 64. Now move the cursor to the Top View. How far down do you like your pavilion break facets to extend? Some faceters prefer about half way from the girdle to the culet. I prefer them cut about two-thirds of the way down to the culet. Move the cursor wherever you desire along the right edge of the main at index 64 as shown in Figure 5.
Figure 5. Defining the extent of the pavilion break facets
When you get to the point, press the Pt on edge (e) key. GemCad will snap to the nearest edge and ask you whether to use the point. If you're satisfied, enter y. You should see the message 2pt displayed. Next, go back to the Cut Facets Menu. We shall cut our break facets at index positions 2 and following. Press Index (i) key and respond with 2. After GemCad cuts the 16 break facets, your screen should look like Figure 6.
Figure 6. After cutting the pavilion break facets
Note that you didn't have to tell GemCad at what angle to cut the breaks; it figured it out from the index and the two points you entered.
We have now completed the pavilion and are ready to transfer the stone. Press >Main Menu function key and then go to the Cut Menu by pressing the >Cut Menu. Press the Xfer (x) key to transfer the stone. Your display should look like Figure 7.
Figure 7. After transferring the stone
It is a good idea to save your work frequently to protect your work from yourself and from power-outages. This is particularly important when designing a new cut. Let's save our work now. Press the Main Menu key and then press the File Menu key. Press the Save (s) key. GemCad will ask you, “Project name?” GemCad is asking you for the name of the file in which to store the project. Enter something like lesson.gem. If a file by that name already exists, GemCad will ask you if it is O.K. to write over the file. If the file does not yet exist, the file will be created. The data files that GemCad reads and writes may have any legal DOS file name (eight characters or less plus an optional three character extension). (It's best for to name your GemCad files with names that have extensions beginning with g so that the file picker can find them without having to change the wildcard.)
It is a good idea to save your work frequently when designing a new stone. This is done with the Save (s) command. With the Save as (S) command, GemCad will always ask you for the file name, whereas with the Save (s) command, GemCad only asks if you haven't yet given it a name. It will still ask if it's O.K. to write over an existing project, however. If you inadvertently exit the program without saving your work, if the power should fail, or (forbid!) the program should “crash,” you can still recover most of your work. Run GemCad press Enter and then immediately press the Undo (u) key (found in several of the menus). This will get you back to just before the last change. To save its work, GemCad uses a file named GEMCAD.BAK in whatever directory from which it was run. It updates this file whenever you make a change to the stone. Note that the undo command will not undo itself.
Lesson 1 is now complete. You might want to take a break now to let the stone and your brain cool off a bit. If you have used the Save (S) as command and specified a project name and the status message “Saved” has been printed in the upper-left-hand corner of your screen, it's safe to exit the program. This done with the Quit (Q) selection in the File Menu.
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