Suggest a suitable material

Discussion in 'Off-Topic' started by strantor, Jan 6, 2015.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    I want to make something like a lazy susan turntable, but flush.
    Imagine a card table top made out of a 1" thick piece of MDF 48"X48", and you cut a 36" diameter hole in the very center. Now I want the inner disk (cutout) to remain exactly where it was, but rotate - I don't want it to be elevated or recessed like a lazy susan bearing would require. I was thinking to use a router to go back through the circular channel with a fluting bit like this :
    [​IMG] (pretend it says 1/2" instead of 3/16")

    and turn it into a bearing race on both sides, then fill up the channel with 1/2" bearing balls.

    I'm pretty sure that idea would suck because the MDF would crumble under heavy load. The load will be pretty heavy, in multiple axes; imagine this lazy susan card table has steel legs anchored to the ground and a pole standing up in the middle of the rotating disk - a fat man standing up on the table grasping the pole should not be able to damage or misalign the disk by throwing his weight against and away from the pole.

    So, what material is better than MDF for this? Obviously steel, but I can't cut steel with a router and fluting bit. I'm thinking some sort of polymer or composite. I've looked into lexan but it's super expensive in these dimensions. UHMWPE would have good lubricating qualities for the bearings but I don't think it's rigid enough. I could possible roll my own micarta or low-temp curing epoxy fiberglass but I would rather not spend all the time working on that. any ideas?
     
  2. djsfantasi

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    1. How big is the table?
    2. How thick is the table top? If the MDF or other material were only 3/4", the load bearing thickness would only be about 1/8". Certainly less than 1/4".
    3. Could you build up the table top butcher block style? You could get much greater thickness, the strength of hardwood, and durability.
    4. Rather than the 'tubular' bearing race, have you thought of something like a lap joint, with bearings in the bottom.
    5. Talking about bearing races, how are you going to fill the race with bearings? If horizontal, gravity will frustrate you. If vertically, you'll only be able to fill half the raceway. And then, how are you going to insert the circle?
     
  3. jpanhalt

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    Jan 18, 2008
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    If I read your description correctly, your plan calls for a 36" diameter ball bearing that will carry large axial/thrust and off-center loads and be made with ordinary wood-working tools.

    I think you will need something under the table to support the rotating part with something like a thrust bearing. You might also consider insetting a standard turntable ring such as these, but larger:
    http://www.mcmaster.com/#lazy-susans/=vcgx2a

    upload_2015-1-6_5-22-41.png

    John
     
  4. sirch2

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    Jan 21, 2013
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    A decent grade of ply should do it as far as the table top is concerned, you could even laminate two layers of 12mm or 18mm together (from experience don't laminate different thicknesses as they tend to warp. BUT I would have thought that the bearing channel would need to be a lot harder than timber to stop the balls creating pits and excessive wear.
     
  5. shortbus

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    Rigid casters. Mount them at an angle that corresponds to the diameter you want to support. The angles are wrong, but like this, with the period being the center point -

    / \
    .
    \ /

    This is just an example of the caster, use what ever is needed to support the weight. One place I worked used this idea for a welding turn table. http://www.harborfreight.com/materi...ighth-inch-light-duty-rigid-caster-41513.html

    edit: the post doesn't show the same as it did on my screen, just imagine that the example is all centered. :)
     
  6. MaxHeadRoom

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    Jul 18, 2013
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    Something like these may work?
    [​IMG]

    Max.
     
  7. #12

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    Your basic idea is correct, but jpanhalt has the answer. It's been done, and better than an amateur can do it.
     
  8. tracecom

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    Apr 16, 2010
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    Am I the only one who finds this a funny picture?
     
  9. djsfantasi

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    No, Just gross...
     
  10. strantor

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    Look, don't judge me. So what, I can't spin on the pole and I need some bearings under me. If you want to see me in action I'll post a video. ;)
     
  11. strantor

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    VBX has those for a decent price and after thinking about it, I think I can make that work, but I wish I could hold it in my hands before pulling the trigger. I assume that those are meant for downward force only, or mostly. My application (not a fat man's pole dancing jig BTW) will subject it to forces up, down, and sideways. Maybe if I got two of them, flipped one upside down, and sandwiched the disk between them it would work well, but now I'm spending over $400 just to see if my hairbrained idea works. I'm going to continue looking for a cheaper and/or more sure solution.
     
  12. jpanhalt

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    Yes, downward force mostly. Calculate the twisting moment from a 22-stone man hitting a 5'-lever at 6 to 10 feet per second (e.g., an NFL lineman hitting an opponent). For that torque, I think you are looking for the impossible with wood that is just 1" thick with the best of wood screws.

    John
     
  13. wayneh

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    Sep 9, 2010
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    For the wooden platform I would use plywood, as thick as necessary. If you need to laminate multiple layers, I'd use glue and a maybe few recessed bolts. You could lay laminate on top to cover the bolt holes and provide a very durable surface. Assuming the back does not need to be smooth, you could lay support beams across the back to get a lot of strength and stiffness without so much plywood thickness.

    For the axle, I'd consider using...an axle. You can buy a trailer spindle bearing that would easily handle the loads. I'd use a disc brake drum - with the right hole pattern - with the spindle, to distribute the stress where it connects to the wooden top.
     
  14. strantor

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    1. the table doesn't exist yet, but I'd like to make it 48"x48"
    2. I'm thinking about 1" should be ideal. possibly 3/4"
    3. Yes, I could, but I don't have a multi-ton press, so there would likely be some gap
    4. I think that's basically what the lazy susan bearings (like jpanhalt linked to) are - That scheme would support top load, but side load would try to lift it up on one side. Unless there's a top lap joint with bearings on top as well - a sandwich again.
    5. I was imagining drilling a diagonal "loading hole" and passing the bearings into the race, then plug it. It would probably leave a snag spot though. I haven't 100% worked that out.
     
  15. strantor

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    I don't think my mind's eye sees what you're trying to show me. There won't be much room for any casters unless they're super tiny. Here's the drawing I made initially, as an idea what I'm after. In the drawing I'm using some simple lathe-made bobbins as rollers (or could be made with large shank bolts w/ large washers). I don't think these rollers will work because I imagine the bobbin flanges will eat up the edges of the MDF.
    rotable.png
    rotable2.png
     
  16. strantor

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    I need the bottom free of obstructions. I gave the analogy of the fat man on top of the table to illustrate that rigidity is needed in all axes. A more appropriate analogy would be: The disk in the table should be able to rotate freely, without lifting or dipping on any side, as a fat man swings from the bottom of the disk on a pendulum.
     
  17. #12

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    Just a note about gluing plywood. I needed some 3" thick plywood so I glued (3) one inch pieces together, sandwiched them between a pair of 1/2 inch thick steel plates and parked a truck on the stack. It squeezed out so much glue that the assembly failed.

    The moral of the story is: Don't use all the pressure you can find.
     
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  18. djsfantasi

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    Re: 2 - As far as the table thickness, look at the sketch I made of your original idea. I was trying to make a point in my earlier post, that 3/4" is insufficient to support the bearings. I think 1-3/4" is a minimum. Choosing a hard wood is critical, too. Maple or Oak, I'd think.
    Untitled.png
    Re: 3 - I don't think you need a multi ton press. A good selection of pipe clamps would likely be sufficient for a 4'x4' table top.
    Again, in #4 remember that the lap joints need a minimum thickness to support the bearings. And a lap joint sandwich would be 2" or more in thickness. Maybe more when accounting for the space of the bearings.
     
  19. Wendy

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    Mar 24, 2008
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    The object in post #12 reminded me strongly of a microwave carasel bearings.
     
  20. shortbus

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    Quote Strantor, "I don't think my mind's eye sees what you're trying to show me. There won't be much room for any casters unless they're super tiny. Here's the drawing I made initially, as an idea what I'm after. In the drawing I'm using some simple lathe-made bobbins as rollers (or could be made with large shank bolts w/ large washers). I don't think these rollers will work because I imagine the bobbin flanges will eat up the edges of the MDF."

    I didn't realize the bottom had to be free too. The casters would have been mounted to a base and then the platform setting on top of them. Can I ask what your building? Or is it top secret?
     
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