Drill a 100% Centre in a Ball Bearing

faavs730222

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Hi, I am busy making Mr Pete's Wiggler Center Finder. I am really struggling to drill the hole 100% center in the ball bearing. It is always a bit off center, causing the needle not to really run center. I am busy now with my forth try. I tried a jig that is saw on the net, where you basically clamp the ball in a hole just as big as the ball. I uploaded a drawing showing how the hole comes out every time. It is really frustrating because I really need a accurate center finder for the milling machine and I am unable to find the wiggler type in South Africa, that is why i were so glad when i saw Mr Pete's Videos on making a Wiggler. I would really like to work on my accuracy because what is the use having all the expensive machinery and the machinist are not able to work accurate.
Any Ideas would be appreciated.

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If you want the hole in the center of the ball, you will need to be spinning the ball, not the drill. The ball will need to be centered so it spins without runout, and then the hole drilled undersized and finally bored to the finish diameter. A drill will only follow an existing hole, but will not move the hole where you want it. A boring bar can move the hole center. Drilling a hardened bearing ball is no easy task, to have it on center makes the task more difficult yet. I just went and looked at my old Craftsman wiggler set, which has three wiggler arms with balls for the pivot and one also has a ball for sweeping the work. All the balls appear perfectly centered. Grinding a small flat on the ball would give you a flat place to start the hole, and might also get under some of the hardest surface skin. The holder socket where the pivoting balls mount in also needs to spin true on the mill if you want zero runout in the needle. On commercial units the balls might be purchased soft and then hardened after machining the holes (and threads?) Not an easy project! Please let us know how it works out and what ideas you used...
 
You would have to anneal the ball to drill it, ream it to size and re harden it; I think most all bearing balls are hardened all the way through, although they can be bought soft. There is no real need to harden the ball to be used as a wiggler. I do not agree that the ball must be perfectly centered (how perfect is perfect?). It is the end of the "needle" that is made to run true, which I do by holding my 6" rule up against it while in rotation, bearing against it until the point runs true. I do roughly the same thing with the .100" point, by roughly truing it then creeping up on the part that I am referencing until no gap is visible, being lit from the backside; some folks approach the work , touch it, and let the diameter part run off sideways; I do not think this is the correct approach.
For the other type of edge finder, the cylindrical type, a small flat ground on the contact surface will increase its sensitivity, the flat need be no more than a fat 1/32" wide.
 
In spinning tops, we use a ball bearing as the contact point of the top. Sometimes it's ceramic, sometimes tungsten carbide, and sometimes more exotic material like ruby or sapphire. It's a real drag when the exotics chip. I had that happen, and came up with a plan to drill it out. The spinning top has a typical flat bottomed blind hole bored into it on center with the bearing pressed in. If you were to replicate this setup, you could hold the bearing in place. Drill a smaller hole all the way through the holder so that you can press the bearing back out (no longer a blind hole). There should be enough in this video that I made for you to get the key concepts that Bob mentioned above. Spin the bearing, not the drill.

By the way- I show the dremel diamond drill bit I used to drill the very hard ruby in the video. In my case, I simply wanted the bearing out of the blind hole. The shattering/brittleness was of no concern. Your case would be more picky.

 
If you want the hole in the center of the ball, you will need to be spinning the ball, not the drill.

All things being equal, machine, tools, material condition and set up, choosing to turn the work or the tool when drilling will make zero difference, one may drill in a lathe by spinning the work or drill in a drill press by spinning the tool.

If conditions are not equal such as drilling in a lathe that lacks sufficient spindle speed it will not be ideal, a mill would be a better choice given a higher spindle speed. I should imagine that the major problem is incorrect tool choice, a wobbly machine and position errors from the start.

As a side note what are the applications of a wiggler that an edge finder or center finder will not accomplish? I've worked in machine shops for 30 years and have never had one and have never seen anyone in a commercial shop use one, it is entirely possible that I am missing some application for it.
 
All things being equal, machine, tools, material condition and set up, choosing to turn the work or the tool when drilling will make zero difference, one may drill in a lathe by spinning the work or drill in a drill press by spinning the tool.

If conditions are not equal such as drilling in a lathe that lacks sufficient spindle speed it will not be ideal, a mill would be a better choice given a higher spindle speed. I should imagine that the major problem is incorrect tool choice, a wobbly machine and position errors from the start.

As a side note what are the applications of a wiggler that an edge finder or center finder will not accomplish? I've worked in machine shops for 30 years and have never had one and have never seen anyone in a commercial shop use one, it is entirely possible that I am missing some application for it.
Wreck, this is about centering the hole in the ball, not just drilling a hole...
 
The one advantage of wiggler over center finder is its very slim, other than that I think a center finder is more accurate and easier to use. I use my wiggler maybe once a year, edge finder almost every time I am on a manual mill.
 
I understand, however you opined that one must rotate the work rather then the tool, please explain this if you will.
Simply that drilling a hole in the center of a spinning part tends to center the hole on the axis of rotation, as we commonly do on a lathe. Note that I did add that the hole would then need to be bored for an accurately centered hole. I also noted that the ball needed to be spinning true with the center of rotation, and that a flat spot on the ball was needed to get a straight start. Is there an error with my thinking?
 
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