This is a guide on how to build a reasonably accurate jig for drilling a hole in a sphere with a hand drill. Following this step by step is very important to get successful results. There are basic measurement skills involved. The more accurate the measurement combined with the ability to match that measurement to the proper tool, the more successful your results will be. There is probably room for improvement to this technique.
Step 1: Parts & Tool List
•bolts(2), washers(2 or 4) & nuts(2)
•hole saw or spade bit that corresponds to the size of the ball
Step 2: Determining Measurements
I wanted to drill a hole in a 1" ball, so in this instructable all of my measurements will relate to that size. it is easy to adjust this jig for a sphere of a different size but once the jig is created it will only be accurate for the size of sphere it was created for. First, measure the size of sphere you would like to drill into, in this case 1". You want the middle layers to be roughly the same width as the diameter of the sphere. I used 1/2" plywood for my jig and 4 layers. In my example my ball is 1", so the two middle layers are 1/2" and they add up to 1".This technique can be done with as little as three layers or several if necessary. I wouldn't recommend using layers any narrower than 1/2" for the top and bottom layers. The top and bottom layers will be your drill guides, so, for accuracy's sake the thicker the better.
Cut your pieces to be the same size with sufficient amount of area around your ball. You want enough space to put two screws in each end and plenty of area around your sphere to be able to drill into it without compromising the strength of the jig. It will be easier to assemble if the pieces are cut the same size.
Step 3: Marking, Clamping and Drilling
In my example there are 4 layers sandwiched together. Number the layer accordingly and put an index mark so they can be put back together exactly the same way. Here I used a line next to my numbers. Mark it so that it is obvious how it goes back together.
Sandwich your pieces together and clamp securely. Measure your bolts and drill a hole with the proper size drill bit on one end of the jig. Insert the bolt and tighten the washer & nut. Keeping the clamp on, drill another hole in the other end of the jig. Try to drill as straight as you can, this will help with the accuracy of the final result. Remember we're trying to do something accurately without the proper tools so any effort you make to be a precise as you can will help. Assemble the bolt, tighten everything and remove the clamp.
Step 4: Pilot Hole
Determine what size hole you want in your sphere. Find the corresponding drill bit and drill a hole in the center (both lengthwise and width). Drill the hole all the way through the jig. If your jig is too wide drill in from the top as far as you can. Then take the jig apart and remove the top layer,put it back together aligning your index marks and drill the rest of the way through. Write the size of the bit next to the hole.
Dis-assemble the bolts and remove both the top layer and the bottom layer of your "sandwich". Align the two middle layers together matching the index marks and bolt them together. You now have the middle layers aligned and bolted with a hole in the center the size of what you want your final hole in your sphere to be.
Step 5: Making a Cavity
Measure your ball and obtain the corresponding drill bit or hole saw. A hole saw in this instance would probably be more accurate than a spade bit. My final result didn't have to be super accurate so I used a spade bit.
The hole that we drilled in the center is going to be a pilot hole to guide the bit you use to drill your cavity for the sphere. A bit to widen the pilot hole is ok, just do not drill a hole larger than your tip of either the spade bit or the core bit of the hole saw. Be patient and let the drill do the work don't force it, and try to be as accurate as you can. You want the drill to naturally follow the path of the pilot hole. Drill all the way through your center pieces.
Step 6: Drilling Your Sphere
Now take the bolts out and re-assemble with all pieces of your "sandwich", again note the index marks. Confirm that everything is oriented in the right direction and each side is facing the same direction as it did when you marked it.
So you now have several layers of wood with a cavity inside that is the size of your ball. You can insert your ball by loosening the bolt on one end and removing the other bolt or by removing the top layer completely, insert sphere and confirm that your index marks line up, re-assemble, and tighten the bolts. Get the drill bit that corresponds with the hole in the center of the top piece. This should be the drill bit that is the size written on the top of the jig. Carefully insert the bit in the hole and drill into your sphere, the hole in the top piece should keep your bit in line with the hole in the bottom piece. Try to be careful not to influence the bit to veer from it's intended path. Drill all the way through, if you want a hole that goes completely through the sphere, or drill to the depth you want, remember to subtract the top layer depth when measuring how deep you want to drill. If your bit isn't long enough you can flip the jig over and drill from the other side.
Step 7: Parting Thoughts...
You should now have a sphere with a hole in the center. it should be reasonably accurate if all the steps went well. I want to add a few extras that aren't detailed here but are worth noting. On my project I wanted additional holes on the sides that were perpendicular to my other holes. Since my "sandwich" layers were an even number, making the center essentially between two layers, I was able to put a wire through the holes and assemble it starting with the center layer and drill a hole 90° from my other hole. I'm sure there are several ways to improve on this design, feel free to comment with any additional details or alterations that might improve it!
Step 8: New Update
I decided to document the process of getting perpendicular holes just in case not everyone was following along. The 1st photo shows another jig after I made alterations to make additional holes. I used a Dremel tool to carve a groove in the center of the jig. I inserted a couple of nails to hold the ball in place, re-assembled the jig and drilled my perpendicular holes.Since my goal for this sphere was to have a set of holes on top/bottom and left/right sides, I inserted another piece of wire in a groove perpendicular to the groove before and drilled an additional hole in the back of the ball.