Cutting and drilling round objects is both difficult and dangerous. This is a step by step guide to making a jig to help drill spheres.
I recently posted a similar Instructable about how to make a jig for cutting and drilling cylinders which can be viewed here (https://www.instructables.com/id/Safely-Cut-a-Chane...
You will need:
Plywood (about 14 by 6 inches or more)
4 3.5 inch 1/4 20 bolts
8 1/4 inch washers (or 4 washers and 4 t-nuts)
4 1/4 20 wing nuts
1 inch forstner bit (or spade bit)
2 inch forstner bit (or spade bit)
5/16 inch drill bit
Step 1: Mark, Measure and Cut
Cut your plywood into one 6'' by 6'' piece and one 6'' by 8'' inch piece. The larger piece will be for the bottom of the jig and will allow for easier clamping.
Next mark an X in in the middle of the 6'' by 6'' piece to find the center. Also make marks an inch away from each corner on the lines making the center X. The center X will be for drilling the hole that holds your sphere and the four corner holes will be for the bolts clamping everything together.
Step 2: Drill
Stack the two pieces of plywood with the square piece on top. Line the square piece up with 3 of the 4 sides of the rectangular piece. Drill a hole with the larger drill bit directly in the middle of the two pieces. It is best to clamp the pieces on top of one another to ensure that the holes are lined up perfectly.
Use the 5/16 drill bit to make a hole at each of the marks you made an inch away from the corners.
Switch to the 1'' forstner bit and drill 3/8 inch deep pockets each of the 5/16 holes. Drill matching pockets on the bottom side of the rectangular piece too. These pockets will be where the washers or T-nuts go and also will create a space for the head of the bolt to rest so that the jig lies flat on the bed of the drill press later.
Try to keep the two pieces of plywood lined up well throughout all of this drilling. It will be easier to bolt everything together if the two sides match perfectly.
Step 3: Add the Hardware
If you are using T-nuts insert them into the pocket on the bottom of the larger rectangular piece of plywood. and thread in the bolts. If you are using only washers insert them into the hole and thread a hex nut on the other side to keep the bolts in place.
Next, press in the washers into the holes in the smaller square piece of plywood and place it on top of the bolts. Thread the wing nuts on top of the bolts and your jig is pretty much finished.
If your marking and drilling was precise it should fit in any orientation. If your jig is like mine and the marking was not perfect it will only fit in one orientation. In this case it might be a good idea to put a directional mark on the top piece to remind you which orientation fits best.
Step 4: Drill Your Spheres
Now you are ready to safely drill holes in spheres. Open up your new jig as far as possible and place your sphere in between the plywood pieces. This jig will only work for spheres that are large enough to make contact with the edge of the hole before touching the table. Tighten the wing nuts on the top evenly to clamp the sphere in place.
Once the sphere is securely clamped in place you can line up a drill bit on the center of your sphere and drill away. I used this jig for a project that will be appearing on Instructables soon.