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IndustryArena Forum > WoodWorking > Everything in between > How to Mill or Drill 3/4" Hole in 3" Hard Rubber Spheres
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  1. #1
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    How to Mill or Drill 3/4" Hole in 3" Hard Rubber Spheres

    There isn't much on this forum related to rubber materials that I can see but I hope someone can provide some advice, or where I might find the resources to solve this problem. I need to drill or mill or punch or otherwise create, 3/4" holes through dead center of 3" diameter hard solid rubber spheres. The material is slightly compliant (shore A durometer ~80). The dead center I think I have figured out - but ideas welcome :-). The problem lies in creating the hole >3" deep without burning the rubber or binding the bits. I've tried pilot holes, hole saw bits, drill press, hole saw with milling machine using water, soap, oil, graphite, silcone, and even WD 40 as lubricant. In all cases (except the small pilot holes) the compliance of the rubber ends up binding the bits. I'm attempting to freeze the material next before milling but I am doubtful this will work unless I freeze at far colder (liquid N2) temperatures than I have readily available. One might say just mold the spheres with this hole in the center but I am trying to avoid that tooling which is extremely cost prohibitive and out of the project scope entirely. Although not milling, does anyone have experience with arbor punches? Thank you in advance for ideas or redirection of this post./skidog

  2. #2
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    Re: How to Mill or Drill 3/4" Hole in 3" Hard Rubber Spheres

    Core drill, and LN is about the only option IMO.

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  3. #3
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    Re: How to Mill or Drill 3/4" Hole in 3" Hard Rubber Spheres

    I have used liquid air (hold can upside down) you can get at office supply stores for "coolant" during machining of rubber and some plastics. Not as cold as LN but readily available.

  4. #4
    Community Moderator ger21's Avatar
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    Re: How to Mill or Drill 3/4" Hole in 3" Hard Rubber Spheres

    I've used one of these carbide forstner bits to drill holes in hockey pucks with very good results.

    Freud Tools | 3/4" (Dia.) Forstner Bit

    Might be a little short, but if you can clear the chips, and go through in one shot, it shouldn't get too hot I don't think, unless the material is just too soft.
    Gerry

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    http://www.thecncwoodworker.com/2017.html

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    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  5. #5
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    Re: How to Mill or Drill 3/4" Hole in 3" Hard Rubber Spheres

    I'll be trying the 0deg F, and LN2 next round. The Forstner bit suggested by ger21 looks good to try too. Hockey puck is, if I recall, harder material than what I'm working with but I like the idea of that style bit. I think part of my problem is the compression force I need to hold this sphere in place while drilling. The material surrounding the hole being drilled is too soft to support the hole I'm making so the compression of the entire sphere continues through-out the drilling. A redesign of the application might allow me to drill two or more tiny 'pilot' holes through which I could place small steal rods of ~3" length then tighten the vice on those and they would act to keep the sphere from rotating and I wouldn't need to compress the actual rubber to much degree. Unfortunately, these extra holes would need to be filled later to create a smooth roller.
    You all have me thinking about options and really appreciate your input. (it all comes down to keeping the soft smooth sphere from moving while drilling and not compressing the material I believe) Thanks a bunch.

  6. #6
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    Re: How to Mill or Drill 3/4" Hole in 3" Hard Rubber Spheres

    I'd say cast the spheres in rubber with the holes in them; you can use a metal cylinder to form the holes (injection-mold push-rods are ideal). You can get liquid 2-part urethane in any durometer you want between hard and squishy. You can machine a metal mold or use silicone rubber to mold a sphere. That's going to be a lot easier than drilling accurate holes in rubber balls, or holding onto them without distorting the holes once you let go.See Smooth-On, Inc. - Mold Making & Casting Materials Rubber, Plastic, Lifecasting, and More for the rubber. It's not really that hard or expensive to do, but you can wait until after you've gone through another attempt at machining this stuff before you try it.
    Andrew Werby
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  7. #7
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    Re: How to Mill or Drill 3/4" Hole in 3" Hard Rubber Spheres

    You may want to think about holding them in a vacuum pot chuck.

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