Venerable Lapdog

he Fine Art of Field Collecting for and the Making of Spheres

By Jay E. Bates

Making of spheres is not difficult but it takes large rocks and much time, usually from 24 hours to 50 hours of sawing on large rock saws and grinding and polishing on sphere machines. Softer material such as alabaster, onyx, and marble will cut faster and are desirable for first time sphere cutters. The ideal finished size for most spheres to maximize value and desirability is about four inches. Because of the size of material needed to make a sphere, it can get costly to buy all your material. Luckily you can go on SFGMS club field trips and collect large rocks that make ideal spheres.

Part One: Finding that One-of-a-Kind Rock to Make a Sphere

Some of my favorite places to search for large rocks suitable for spheres on field trips are the Monte Cristo Mountains in Nevada, Davis and Lassen Creek in California for sheen obsidian, many onyx and marble quarries and locations, and the Clear Creek area for jadeite. There are also many jasper and jasper/agate locations in many states that can also make very desirable spheres. I usually look for rocks on field trips that are about 6 inches in the minimum width and wet them down to get a good view of the colors and patterns. The farther you walk away from parking areas the more likely you are to find large enough rocks for spheres as most people are not willing to carry large rocks any distance. You should try to select a rock with a minimum of cracks and holes. However, a vug with crystals can be desirable feature for some spheres. I have also made some nice spheres from Morgan Hill Poppy jasper with cracks since the material seems to stay together while grinding even when shot through with cracks. Using such material does require the use of Opticon or similar stabilizer with rock dust of the same material before sanding. It takes a good eye to visualize a final sphere from your rock and selecting for pleasing colors and patterns makes the whole process worthwhile in the end. Some material such as sheen obsidian or star rose quartz are always desirable for spheres as you do not have to worry about orientation for optical effects since with a sphere you always get the desired optical effect on a couple sides of the sphere.

Another good place to look for large rocks for spheres is at weekend rock sales. Many times excellent material can be found at such sales at reasonable prices. Don’t be afraid to negotiate a lower price as usually the sellers do not want to end up with large rocks on their hands after the sale. Similarly, once in awhile you can score a nice rock for a sphere at the end of a rock and gem show since the dealers are reluctant to lug large rocks back to their vehicles.

Part Two: Sawing Your One-of-Kind Rock into a Cube and Later a Octadecagon

Once you get your unique specimen home you will need to wash it off and measure its least dimension to determine how big of a sphere you can roughly make. Most of you will be using the large saws in the shop. BEFORE YOU USE THE LARGE SAWS IN THE SHOP YOU WILL NEED TO BE CHECKED OUT BY AN INSTRUCTOR IN THE USE OF THE LARGE SAWS. If you bend a blade in the large saw it costs a lot of money to replace. If you do bend a blade you may have to pay for it. I am around on most Friday evenings, when I am not out field collecting, to help with sphere making. On Fridays, I or another instructor will help you once or twice with setting up the large saws until we are confident you are using the right procedures.

When placing a rock in the two larger saws place a block of wood in the vise opposite to the rock to provide a counterforce to the rock in the vise. Remember the vise acts like a teeter-totter on the connection in the middle. Use wooden wedges to get maximum grip on the rock. Finally give a yank on the rock with your hand to see if you can pull it loose before starting the saw. If at any time during the sawing you see smoke or hear a significant change in noise coming from the saw stop the saw and see what is going on. Get help if necessary.

To begin sawing first find the flattest and largest side to your specimen, make your first cut parallel to that side and as close to that side to minimize lose of material. Once that cut is made, lay the flat cut side down on the saw carriage and make the next cut on the flattest and biggest side at 90 degrees from the first flat cut side.

You will now have two flat sides at 90 degrees from each other. Keep one of the flat sides down on the carriage and the other flat side up against the from of the carriage and make another cut minimizing the loss of material but getting another side 3/4 to nearly the same size as the first two cuts.

After the third cut, get out your tape measure and measure the least dimension between either flat side and opposite sides near where the center axis of your sphere is going to be. This is going to be the maximum size your can make your sphere. Choose a size slightly less that your determined maximum size and make a fourth cut that distance from one of the flat sides with again one flat side on the bottom of the carriage and another flat side up against the front of the carriage. Keep doing the same for the last two cuts until you have a cube.

Once you have a cube you will now have to mark your cube with lines as to where the cuts are going to be made to get an eighteen sided solid (octadecagon) that can be put into the sphere making machine after some rounding of the corners. The following values are used to scribe your cube for the cuts:

W is the width of the cube. X is the distance in from an edge of the cube to where a line is scribed parallel to the edge of the cube. B is the width of each of the eighteen sides of the final eighteen sided solid. Use an aluminum scribe to scribe the lines.

W=X+X+B =2X+B X=.707B* B=1.414X W=3.414X X=.2929W

*From trigonometry for a 45 degree angle to get the equal widths on all the sides of your eighteen sided solid and a maximum sized sphere from your cube.

Original Cube Width X X in Sixteenths
________________ ______ ____________

1.0 .29 5/16
1.25 .36 3/8
1.5 .44 7/16
1.75 .51 1/2
2.0 .58 9/16
2.25 .65 5/8
2 .5 .73 3/4
2.75 .80 13/16
3.0 .87 7/8
3.25 .94 15/16
3.5 1.02 1
3.75 1.09 1 1/16
4.0 1.16 1 3/16
4.25 1.23 1 1/4
4.5 1.31 1 5/16
4.75 1.38 1 3/8
5.0 1.45 1 7/16
5.25 1.52 1 1/2
5.5 1.6 1 5/8
5.75 1.67 1 11/16
6.0 1.74 1 3/4

Once your lines are scribed you can use either a jig or a block of wood to cut at a 45 degree angle from each flat of the cube along the lines scribed on each flat. There is a metal jig for the middle large saw in the shop and a wooden jig that can be clamped to either of the two larger saws. You can also use a plain old block of wood cut at a 45 degree angle to tilt your cube at 45 degrees to the saw blade.

Lines are scribed on the cube using an aluminum marking scribe or permanent marker.
Once your lines are scribed you can use either a jig or a block of wood to cut at a 45 degree angle from each flat of the cube along the lines scribed on each flat. There is a metal jig for the middle large saw in the shop and a wooden jig that can be clamped to either of the two larger saws. You can also use a plain old block of wood cut at a 45 degree angle to tilt your cube at 45 degrees to the saw blade. With your cube now cut and tilted at 45 degrees in the saw you now need to cut off the corners to get an octadecagon. This will take twelve cuts.

After the octadecagon is completed you will need to take it to a rough grinding wheel to round off the corners even more; in our shop that means using the 80 grit diamond wheels. Do not push the octadecagon against the diamond wheel, let the wheel do the cutting without excess force as that wears out the diamond wheels prematurely. Also do not grind on the very edge of the wheel as that can remove a strip of diamonds from the wheel.

When the corners have been substantially ground off, it is time to place the rounded octadecagon in the sphere grinding machine. We have one sphere grinding machine dedicated to rough grinding and one for sanding. There is also a dedicated sphere machine in the polishing room for final polishing. All of our sphering machines were built by Richardson’s Ranch in Oregon, who is no longer building sphering machines. I have built several sphering machines from scratch as discussed in an article in the June 2005 Rock and Gem Magazine entitled “Bates’ Sphere Machines” Please feel free to contact me if your are interested in building your own sphere making machine.

With the rounded octadecagon, in the rough grinding machine in the corner of the shop, the spring tensions need to be adjusted to get the right force of the grinding cups against the octadecagon. Also the angles of the grinding cups needs to adjusted to get the proper motion of the octadecagon in the cups. A “random walk” motion of the octadecagon is needed to get even grinding on all sides of the octadecagon. If the octadecagon does not move randomly in the cups during grinding you will only get circular grooves ground into your octadecagon. If that happens, you will need to remove the octadecagon from the sphering machine and return to the grinding wheel to totally remove the circular grooves from your octadecagon. The angle of the grinding cups is adjusted using an end wrench to move one of the grinding cups toward the middle or away from the middle of the sphere machine and tightening down the locking nut on the cup hinge when you have the octadecadon doing the proper “random walk” in the sphering cups. As you grind, you will eventually arrive with a round sphere except for some round dots. You will need to keep grinding until all the round dots are ground away. Once the round dots are ground away you have a sphere.

After grinding, the sphere is placed in the sanding sphere machine and various grits of silicon oxide are applied to the sphere with a steady water drip to make a sanding slurry. You will use coarse grit, usually 220, then 400, ending with 600, to remove all the scratches from your sphere. Adjustments to the sphering machine are similar to those you used for the rough sphere grinding machine. The sphere is then thoroughly cleaned with soap and water before placing in the polishing sphering machine for final polish. Final polish is obtained using a slurry such as water with tin oxide or cerium oxide or other similar polishing compound. Run in the polishing sphering machine until the desired polish is obtained. Your sphere is now complete for you to proudly display. Congratulations!