| How To Make a Cabochon, page 3 by Paul W. Cinnamon Step #5: GRINDING TO THE TEMPLATE LINE Grind the outer perimeter of the slab down nearly to the outline with the coarse grinding wheel or lap. Typically this wheel or lap will be in the range of 80 to 100 grit. When making this initial cut outlining the cab, I recommend trying to avoid any bevel. Cut the girdle of the outline as near to 90 degrees from the flat sides of the slab as possible. If the material is porous, or has a tendency to chip along the edges, you may need to move to the next higher grit wheel or lap and very slightly bevel the edges. This wheel or lap will typically be about a 180-grit. You may find it better to finish cutting with this grit until your cab fits perfectly inside the template cutout. STEP #6: DETERMINING THE TOP & FINISHING THE CAB BACK Visually inspect the cab to determine which side you wish to be the top. After making this determination, although it isn't necessary or required, I usually finish the flat backside of my cab. First I grind away all saw marks using the 100 grit wheel and then completely go over the area again with the 180 grit wheel. Then I move on to sanding, first with 220 grit, then 600 grit, 1200 grit, and finally 14,000 grit. I don't spend a lot of time doing this, and I don't polish the back, but the few minutes spent will produce a more professional appearing cab. I don't bother to dop the cab for this operation, but just hold it loosely with my fingertips. STEP #7: MARKING GUIDELINES ON THE CAB Lay the cab on its flat back side at the edge of a table with a square edge (rounded or beveled won't work), or on the edge of a flat square edged board. Using the marker described in Step #2, observe that the marker has about 5 stairsteps between the marker barrel and the felt tip. Rest the marker on one of these steps on the table edge or board edge with the marker barrel horizontal, and holding the marker in a steady position, slowly rotate the cab with your other hand while lightly contacting the felt tip. This should produce a very even parallel line around the outside girdle edge of the cab. Ideally, this line should be about half way between the bottom and the top of the cab. To find the exact center, taking care to hold the marker in the same position, turn the cab over and repeat the process. The space between the two lines should be the exact center of the cab girdle edge. Return the cab to its back and find another step on the marker tip that will produce a mark about 1/4 of the way up from the bottom of the cab girdle, and rotating the cab as before, scribe another line around the girdle parallel to the centering lines. Repeat this procedure again making another parallel line about 3/4 of the way up from the cab base. These lines will be used as guides to produce an even bevel on the top of the cab. A couple notes of caution regarding the felt tip pen. These pens are not inexpensive, and their life can be greatly extended if the tip is never allowed to dry out or become contaminated with oil, water, or rock dust. Wiping the slab dry of moisture and then cleaning it with denatured alcohol before marking will greatly increase pen life. Next, I mark a crosshatch series of lines spaced about an eighth of an inch apart over the top of the cab. These lines will be very helpful in keeping your cut even on the face of the cab, and in eliminating the possibility of leaving a flat spot in the center of the cab face. If you are concerned about the ink penetrating into the cab, you may mark these with an aluminum marker, or even a lead pencil. |