Drilling holes in spheres

[mklotz]

A friend asked me to drill holes in some wooden spheres. The procedure I used to get the holes on diameter can be used on spheres of almost any diameter and material.

I drilled holes of diameter a bit smaller than the sphere diameter in some plywood plates. Bolts through these plates and anchored in the mill T-slots allowed me to trap the ball and clamp down on it so it couldn't move under the action of the drill. Here's a view of the setup from above...

This side view shows the bolts and the way the sphere is trapped...

and the finished product(s)...

Once the sphere was clamped, I found its diameter by taking a very slight pass across its top with an endmill. This produced a tiny flat on the top the center of which I eyeballed (hey, it's wood after all). A center in the mill chuck then allowed me to line up on the diameter.