Grinding a flat face on a 1" ball bearing? - Page 2
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  1. #21
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    This is what i'm going to try:

    1. cut a piece of tube - in my case 1/2" and file it flat on both faces.

    2. Place the ball in a machinists vise with the tube holding the ball. Gently add clamping force to the ball using the V-slot in the vise

    3. Put the vise on my surface grinder and go at it.

    I think this is a combo of a few of the suggestions. I'll post when I'm done - just ordered some 3/4" balls off of e-bay.

    Cheers,
    Bob Welland

  2. #22
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    I think the idea behind using a bearing ball to set a clamp is to ensure that the flat bottom of the work is evenly against the bottom of the vise. This makes sense when only one side of the work is flat and you want to mill a surface parallel to that flat side. When the work is clamped you want to ensure that the work does not ride up on the jaws on the vise and introduce air gaps between the bottom of the vise and the one flat side.

    First of all, observe that if you put a parallelogram-shaped piece of work in a clamp it will obviously ride up the jaws. If you put a bearing ball on the side with the low point of contact (POC) it will prevent this:

    </font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">-------| ________________|-----------
    | / R /| high POC
    | B / / |
    | /R / |
    | / (work) / |
    | / / |
    | / R / |
    low | / S / |
    POC |/_______________/ |
    --------------------------
    (vise)
    ---------------------------------------------

    B - flattened bearing ball location
    S - single flat surface
    R - rough surfaces</pre>[/QUOTE]In the diagram above the bearing ball ensures that the work is flat against the bottom of the vise. Without the ball the work will ride up the jaws on the high side.

    Even if the work seems square an unequal pressure between the points of contact on the two sides of the vise combined with a bad contact angle may cause the work to slip on the jaws and move off the bottom.

    GOAL: The goal is ensure that at the point of contact with the highest force the contact angle is pointing down.

    For example, in the diagram above as long as the friction of bearing ball B against the jaws exceeds the upward force of the high POC then the work will stay tight against the bottom. This is because the ball is on an acute slope of the work. If the ball was on the other side of the jaws the work would ride up.

    ROUGHLY RECTANGULAR WORK:

    If the work is nearly flat on its sides it may have a microscopic profile like this on its surface:

    </font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;"> ___
    |_
    _|
    |__
    _|
    __|
    |_
    |_
    _|
    |__
    ____|
    |_</pre>[/QUOTE]In a case like this what happens is that the ball crushes the tiny ridges in the work and forms a convex bearing surface that mates to the ball. As long as the depth of this cavity is an order of magnitude deeper (5-10x) than the surface irregularity then you are guaranteed a clamping force perpendicular to the jaws of the vise.

    In other words the "divot" that is made on the work is what keeps the work from slipping on the jaws and leaving the bottom of the vise.

    You want to use a hard bearing ball because the divot is what makes the system work.

    It is a good idea to use a hardened parallel plate to protect the jaws of the vise from the ball.

  3. #23
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    By the way in "Machine Shop Trade Secrets" the use of the ball is specifically cited for locating the pressure of the vice in its center. If rough sawn stock is put in a vice and does not have parallel sides it will put unequal pressure on the different ends of the movable jaw, not a good thing for the vise. To remedy this Harvey recommends using the ball to locate the pressure in center of the center. Here is the excerpt (from p. 217 -- Blocks):

    "1. Use a modified ball bearing to hold rough sawed stock in your milling machine vice.

    A steel ball with a flat can be used to apply pressure to the center of the vice and the center of rough sawed stock. The ball should be used when there are no parallel surfaces on the stock for the vice to close on. You may have to use the ball a few times to some surfaces roughly square and parallel before you begin the precision squaring process as described in the following paragraphs. The flat on the ball allows the vice to be closed tightly without damaging or indenting the vice jaw. The ball should be large enough so that it can be held in place without smashing your fingers when you close the vice. A three-quarter or one inch ball bearing ground with a flat about a half-inch in diameter works well."

    He then goes on to detail how to make a precision blocks (and plates) on a milling machine. Get the book for details. It is a great book and has a couple hundred such techniques described along with photographs.

  4. #24
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    McMaster Carr has machinable, low carbon, bearing balls, case hardened, rockwell c60. Tough stuff, but if you can get past the case, you're half way there. Also, why wouldn't cylindrical brass, or bronze not work? It won't dimple the work but will keep the work from lifting?

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    Rough the xcess off on grinding wheel-Get bit scrap bar drill/ream hole to drop bearing into.Split saw cut to depth of hole dont split the scrap bar/block in two .Hold in vise
    Last edited by onecut; 04-08-2017 at 11:55 AM.

  6. #26
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    Regular hex nuts have a nice internal chamfer for the threads. This is a quick and readily available "fixture" to support a ball for machining.

    Use one on either side of the ball bearing and clamp in a vice. It gives opposed circular contact areas, which is about the best you can do when working with a sphere.

  7. #27
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    what I did was take a piece of flat bar about 1" long and 3/4" wide and a little thicker than 1/2 the diameter of the ball. Drilled a hole in the center of the block and bored it about .002 smaller than the ball but not all the way thru the block(just almost) Take your ball over to the press and press it in the hole in the block and your done. why all this grinding on the ball. You now have your squaring ball that won't hurt your vice jaw and what little dimple your may put on your part your going to mill off anyway when you square that side. works well for me. Gary

  8. #28
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    Quote Originally Posted by gcgold1 View Post
    what I did was take a piece of flat bar about 1" long and 3/4" wide and a little thicker than 1/2 the diameter of the ball. Drilled a hole in the center of the block and bored it about .002 smaller than the ball but not all the way thru the block(just almost) Take your ball over to the press and press it in the hole in the block and your done. why all this grinding on the ball. You now have your squaring ball that won't hurt your vice jaw and what little dimple your may put on your part your going to mill off anyway when you square that side. works well for me. Gary
    Just hold it in a 5C collet, that is what I did when I had to drill through a 3/4" ball bearing and then drill another hole half way through intersecting the first one at exactly 90 degrees. 5C has plenty of grip.

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  10. #29
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    Toolmakers vise, but my ball is only 1/2" in diameter and I used the surface grinder. The V in the fixed jaw kept it from moving around and a parallel kept it from moving down.

  11. #30
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    When I made my flatted ball I chucked it in my 3 jaw and hard turned it.

    Afterwards I realized I didn't have to make it. I could have taken a spherical nut & washer combination and used it in place of the ball. Added benefit: no Brinell marks.


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