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Drill a 100% Centre in a Ball Bearing

Discussion in 'QUESTIONS & ANSWERS (Get Help Fast Here!)' started by faavs730222, Aug 29, 2017.

  1. faavs730222

    faavs730222 South Africa Active Member Active Member

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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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  2. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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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...
     
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  3. benmychree

    benmychree United States John York H-M Supporter-Premium

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    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.
     
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  4. wildo

    wildo Active Member Active Member

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    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.

     
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  5. Moderatemixed

    Moderatemixed Canada Active Member Active Member

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    PM me with your address and I'll send you a Starrett wiggler set; I think that I have an extra one. I grew up in Zim but am Canadian, glad to help out. Cheers.


    Sent from my iPad using Tapatalk
     
  6. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    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.
     
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  7. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Wreck, this is about centering the hole in the ball, not just drilling a hole...
     
  8. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    I understand, however you opined that one must rotate the work rather then the tool, please explain this if you will.
     
  9. Doubleeboy

    Doubleeboy Active User Active Member

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    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.
     
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  10. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    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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  11. DAT510

    DAT510 United States H-M Supporter - Premium Content H-M Supporter-Premium

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    When I had to drill into a steel ball, I mounted it in a collet on my lathe, also using a collet stop to give the ball an additional "backstop". I then machined a small flat spot on the face, at a diameter slightly smaller than the hole I wanted to drill. This was to keep the center drill from walking around on the curved surface. After center drilling, I proceed to drill the desired diameter for the through hole.

    Hope this helps.
     
  12. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    Not at all, however it is not the spinning part that helps center, it is the tool which is free to move when drilling in a lathe, one would hope that a part held firmly in a lathe spindle is not free to move about if you know what I mean.
    If both tool and part are held rigidly which one rotates is unimportant all other conditions being equal.

    If doing such a job I would never use a center drill to start but a spotting drill, then a center if a 60 Deg. shape is required, center drills are not required to have accurate diameters only accurate angles, they are for making centers not drilling or starting holes.
     
  13. Bob La Londe

    Bob La Londe United States Active Member Active Member

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    My thoughts.

    Find a collet you can put a depth stop in. Put the ball bearing in the collet in your lathe. Use an end mill to cut a tiny flat. Then center drill or a spotting drill, then drill. Use a stub length screw machine drill. If its a good hard bearing it might still not work.

    Even a big heavy center drill will walk a little on a spherical surface. I do something like that to drill the side hole in high pressure injection probes.

    A cheap and cheesy edge finder is a fairly tight bearing assembly pressed on the end of a shaft. Its not super accurate, but its something anybody can make.
     
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  14. whitmore

    whitmore United States Active Member Active Member

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    Consider an EDM plunge tool (the cheapest kind of EDM tooling) onto a rotating
    hardened ball. If the rotation axis is not aligned to the plunge axis, this makes a tapered hole. It's
    relatively easy to press a stem into such a hole. Heck, if you want to get fancy, you can
    do this to a tungsten carbide ball... or boron carbide. If your tool is cylindrical, and at
    least half the diameter of the entry, it makes a clean frustum-of-a-cone cut.

    The ball DOES have to be spun on its axis, which ought not be hard to arrange. Harder,
    is keeping the ball elecrically connected so your rotary holder mechanism doesn't get sparked.
     
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  15. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    All good comments, Wreck. I also agree with the advice on not using a center drill for starting drilling operations.
     
  16. faavs730222

    faavs730222 South Africa Active Member Active Member

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    Thank you very much for all the replies. What I would give to have your experience. The reason I opted to make a Wiggler is because I were not able to find a Center Finder either. I tried to "convert" my Edge Finder to a Center Finder. We are not so Geared for the Hobby Machinist here in SA (I would like to hear form other members form South Africa where they get there tools). You can find the items on ebay or even suppliers themselves on the net, but most of the times the postage is more expensive than the actual item. I am really indebted to people like you, because if I have a problem, I know where I will get help. Thank you again.
     
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  17. quickcut

    quickcut South Africa H-M Supporter - Premium Content H-M Supporter-Premium

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    You can get the UK cromwell/Kennedy tools in SA. I usually order from SATOOL. (other than a customer I have no association with them. ) They have quite a comprehensive catalogue . I just phoned them and they can supply a 5 piece wiggler set for R 200.00 approx.

    hope this helps

    charles
     
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  18. faavs730222

    faavs730222 South Africa Active Member Active Member

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    THANK YOU VERY MUCH CHARLES! Does SaTool have a website, or can you order form them out of the Cromwell Catalogue?
     
  19. quickcut

    quickcut South Africa H-M Supporter - Premium Content H-M Supporter-Premium

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    You can just quote the Cromwell tool catalogue number, phone them quote the part number, from the catalogue . They are online to the main indent agent, so if it is not in stock with them they can get it from the agent. In your case the agent had 27 in stock , when I asked. Hope you come right

    cheers charles
     
  20. Silverbullet

    Silverbullet Active Member Active Member

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    I think his problem starts with the ball getting the flat spot and hole started straight correct. When making the wiggler he should have made the ball and rod one piece . I'd use a ground tool to turn the ball and point out of drill rod then there's no problem centering .
     
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  21. wildo

    wildo Active Member Active Member

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    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.
     
  22. ezduzit

    ezduzit United States Active User Active Member

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    Why not, as long as it provides a coaxial starting hole?
     
  23. Kenny G

    Kenny G United States Steel Registered Member

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    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.
     
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  24. faavs730222

    faavs730222 South Africa Active Member Active Member

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    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.


    Sent from my iPhone using Tapatalk
     
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  25. DAT510

    DAT510 United States H-M Supporter - Premium Content H-M Supporter-Premium

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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.......
     
    Last edited: Aug 31, 2017
  26. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    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.
     
  27. ezduzit

    ezduzit United States Active User Active Member

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    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.
     
  28. whitmore

    whitmore United States Active Member Active Member

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    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.
     
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  29. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    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.
     
  30. faavs730222

    faavs730222 South Africa Active Member Active Member

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    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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