Drill a 100% Centre in a Ball Bearing

If you use a coring bit like I showed in the video, it self centers (well, within the flexibility of the bit) on the round surface.
 
I actually watched the videos 4 of them.
1. Mr. Pete used 5/16" ball bearing
2. he annealed 3 steel one was brass so he didn't anneal it
3. he held the ball in a lathe collet
4. he face off a couple thou for a flat
5. he then center drilled with a #2 may have been#1 center drill 1/8 diameter point
6. then he drilled and tapped a 1/8" hole 1/4" deep
He made it look easy but he did finesse the drilling and tapping so the ball wouldn't push back into the collet or move.
you said you used a jig can you show it to us? This may be the problem.
 
My first attempt, i annealed a 8mm ball bearing. I milled a flat and eyeballed the centre (first mistake). I used a 3mm centre drill to start the hole and drilled it about 4mm deep using a 3mm drill. I do not have a collet set for my lathe so i tried to do it on the mill. My next attempt was to make the jig. I used alu block and centre drilled a 3mm hole. I drilled the 3mm hole deeper to about 6mm. I locked the bed if the milling machine and drilled a 8mm hole 4mm deep on the 3mm hole. Leaving the setup locked in the mill, i took a 5mm alu piece and drilled a 4mm hole through it. I enlarged the 4mm hole to 8mm for 4mm deep. Now the 8mm ball bearing lay snug in the 8mm hole. I clamped the ball with the top 5mm plate in the mill and centre drilled the ball and drilled the hole, but even with this setup the hole was off centre. Will upload pics of jig. I ordered a collet setup for my lathe because it looks like it is the way to go.


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It sounds like you may only have a mill?
Is there a way you can reverse the setup? What I mean is turn you mill into a lathe, clamping the ball in the chuck of the mill and holding the drill bit steady. By turning the ball, hole will more naturally be centered, as others have mentioned. You would still need to machine a small flat on the ball, to keep the drill from wondering, ideally doing this also by spinning the ball, so the flat is sure to be perpendicular to the axis of rotation.

Just trying to think out of the box.......
 
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Why not, as long as it provides a coaxial starting hole?
Like Wreck said, center drills are designed for making 60 degree holes for lathe centers to fit into. The 60 degree taper is also not a good choice for any following drill with a larger point angle because the drill will walk around as it catches on the 60 degree hole edges. Further, it is easy to break off the point of a center drill while drilling in harder materials, often ruining the part while trying to get the broken point out of the hole.
 
...The 60 degree taper is also not a good choice for any following drill with a larger point angle because the drill will walk around as it catches on the 60 degree hole edges. Further, it is easy to break off the point of a center drill while drilling in harder materials, often ruining the part while trying to get the broken point out of the hole.

Thanks Bob. You don't need to use the 60* portion--just the center drill portion. I've been using this in 316 stainless without a problem because I don't have a set of spotting drills yet.
 
Like Wreck said, center drills are designed for making 60 degree holes for lathe centers to fit into. The 60 degree taper is also not a good choice for any following drill ...

If you use the center drill on a piece of scrap held on your mill table, then clamp the ball into that conical
depression, the subsequent drill operation starts on a centered ball.
 
Thanks Bob. You don't need to use the 60* portion--just the center drill portion. I've been using this in 316 stainless without a problem because I don't have a set of spotting drills yet.
Using the 120 degree point of the center drill to spot a hole works fine for a 118 degree drill to follow, I do that sometimes. Needs to be a larger center drill for more than tiny holes to follow. If the center drill is used deeper than just the tip, it leaves a cylindrical hole that can be difficult for the main drill to follow.
 
I would like to thank all that replied, I learned a lot from your comments. I think it is safe to say that my milling machine setup is simply not rigid, accurate enough to drill the hole absolutely center. I looked again at Mr Pete's videos and I will rather use the collet in the lathe as he used and some of you suggested. But through my question I got to know some of you and it is clear that you are always willing to part with your knowledge, and for that I am very thankful. I am busy with a Wobbler Steam engine of my own design and when I am finished I would like to share it with you.

Thank you again.
Anton
 
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