I needed to drill some brass balls and I needed the holes to be consistent and square (tangent?) to the surface of the ball. For this instructable, I used brass balls, but the same technique can be used for steel ball bearings, with the exception that the case hardening of the ball must be ground off on the area where you wish to drill.
- Vertical Mill (Bridgeport) or Drill Press
- Drill Bit(s)
- Ball Mill or Larger Drill Bit
- Two pieces of scrap metal plate or plywoods roughly the same size.
Step 1: Drilling
If you're using a mill, go ahead and center the drill bit where you'd like the hole, then lock down the table. If you're using a drill press, make sure that the table is locked and the vice is secured to the table. The success and repeatability of this setup relies on rigidity.
- Once everything is locked down, take you're first plate, clamp it in the vice and drill through with the same size drill bit you'll be drilling the ball. This plate will be your clamping lid.
- Swap out the drill bit for a ball mill (of the same diameter of your ball bearings) or a larger drill bit. Drill a shallow hole into the plate. The hole should not be deeper than the radius of the ball.
- Test fit the ball to make sure it seats well in the hole, but doesn't sit below the equator of the ball.
- Remove the first plate from the vice, and insert the second plate.
- Repeat lines 1-3 above on the second plate.
- Now you're ready to drill the ball. If you're drilling steel ball bearings, they're most likely case hardened, and cannot be drilled with standard drill bits. Luckily, the case hardening is very shallow. Use whatever grinder you prefer to grind a small flat spot roughly the same diameter of the hole you'd like to drill on the ball bearing.
- Drop the ball into the hole you've drilled on the lower plate. If you've ground a flat spot, ensure this is on the top now.
- Lower the upper plate on the ball and clamp in place. Evenly tighten the clamps. If you're drilling steel balls double check that the spot you ground hasn't shifted.
- Drill away! You can also use this opportunity to tap the ball as I did.
Step 2: Assemble
There are many different applications for a drilled ball bearing, and even more for a tapped ball bearing. Use your imagination and be safe!