Mechanical Engineer Needed
February 16th, 2009Weight
Help me out here.
I want to build a revolving table. On one side, I’ll have my 12″ sliding miter saw. It weighs about 85 pounds. On the other, I’ll have my dry-cut saw and bench grinder. Between the two of them, it’s probably 130 pounds. I want the grinder and dry-cut saw on one surface, and the miter saw on the other. If you don’t know what I mean, I’m talking about a table that revolves on an axle. When one set of tools is upside-down, the other is ready for work.
I was thinking I’d make the table part from two pieces of thick plywood sandwiched around maybe four pieces of lumber going across the plywood. What should I use for the axle?
I have a piece of galvanized fence post about 1 1/2″ in diameter. It would cost me some rigidity, as the big 1 1/2″ hole would go through the crossmembers. But I think it’s strong enough to support the tools.
February 16th, 2009 at 6:36 PM
I’m no engineer, but your plan sounds doable. The only thing is the large hole that you mention: use 2 X 6’s for the sides instead of 2 X 4’s and you’ll be OK. (if I have your plan correctly pictured in my head.)
February 16th, 2009 at 7:39 PM
I’m a EE that plays at being an ME…does that count?
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You’re basically talking about a Composite Struture (kind of like my foam/fiberglass composites for my airplane) where the spacing between the skins is what gives you your rigidity (most of the load is carried in the “skin”). If you wanted to go “super rigid”, you could also bond in a styrofoam core between the plywood sheets, but depending on the size, I’m not sure it’s worth it.
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For “Weight and Balance” (sorry I couldn’t resist thowing in a pilot term…), you may want to balance the Miter Saw on the center of it’s side, and then balance out the grinder and dry-cut saw against each other. Weigh them and compute their moments (moment = weigth X distance) and then position the heavier item inward to match the moment of the other item. The whole thing should balance freely then.
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For bearings and such, you already know about McMaster-Carr and are probably already searching their catalog…right?
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BTW, the plywood doesn’t have to be that thick to be incredibly strong…it’s the separation of the skins that gives the structure strength. Of cource if you are going to attach power-tools to it with Lag Bolts, then thicker is better. The alternative is to put in “Hard Points” (2×4’s?) where the tools will attach.
February 16th, 2009 at 7:41 PM
And apparently I having trouble with my spelling tonight…better go do something mindless like polishing the shower knob.
February 16th, 2009 at 7:50 PM
There are off the shelf components that do what you want. They’re a bit expensive, but not prohibitive. You might also look at trailer axle assemblies. You can just buy the stubs and flanges.
February 16th, 2009 at 8:04 PM
“you may want to balance the Miter Saw on the center of it’s side, and then balance out the grinder and dry-cut saw against each other”
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It’s going to work out that way for reasons of space and ergonomics, regardless. If it helps me turn the thing, even better. The sliding saw will take up an entire side; I figure 40″ by 20″. The dry-cut saw is like a miter saw; it has to be positioned near one end of the table, with the blade parallel to the axle. If I turn it, the grinder will interfere with the workpieces. The grinder has to face the other end, or else the dry-cut saw may interfere with it.
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“The only thing is the large hole that you mention: use 2 X 6’s for the sides instead of 2 X 4’s”
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Not sure I can. If the table is too thick, the finished assembly will be too tall to rotate inside the cabinet.
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I’m hoping to avoid bearings. Will I really need them? It’s not like this thing will turn more than twice a month.
February 16th, 2009 at 9:07 PM
not bearings for the sake of the ease but the load. Email me a sketch and i can show you how i might do it.
February 16th, 2009 at 9:09 PM
Dont use an axle, use a ring bearing on a pedestal. That way you dont have to worry about weight and balance.
February 16th, 2009 at 9:42 PM
Hi Chris,
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“Dont use an axle, use a ring bearing on a pedestal. That way you dont have to worry about weight and balance.”
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If you mean a Lazy Susan style ring bearing, I think Steve wants the platform to flip end-for-end (where one set of tools is actually upside down while your using the other set). Or he may be intending to flip it “front-to-back”…I’m not quite sure. Regardless, that kind of “flipping” with hundreds of pounds of weight, would be a lot easier if things were in balance.
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As for the wood “bearings”, maybe it would help to have a couple of wood bearing blocks interior to the table?
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Fun project…post pictures!
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Now to go back downstairs and paint another coat of clear-coat on the new shower knob.
February 16th, 2009 at 9:47 PM
Steve said:
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“I have a piece of galvanized fence post about 1 1/2? in diameter. It would cost me some rigidity, as the big 1 1/2? hole would go through the crossmembers.”
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Okay, so you already have bearing blocks interior to the table…must be the Clear Coat fumes getting to me. 🙂
February 17th, 2009 at 12:03 AM
Go buy 2 engine stands. If they don’t work out for this, something else will come up.
February 17th, 2009 at 8:36 AM
What’s a lag bolt?
February 17th, 2009 at 8:44 AM
Don’t you mean a rotating table, as opposed to a revolving table? To my mind, a rotating table would have the machines mounted all on the same plane and would spin in lazy susan fashion. Are you referring to this, or a table top that has something mounted on each face, where when one tool is in use, the other is suspended below it, upside down?
February 17th, 2009 at 8:47 AM
Never mind. I’ll start reading the whole post before I move on to the comments.
February 17th, 2009 at 10:56 AM
What an amazing idea! Too bad it will never catch on.
February 17th, 2009 at 12:43 PM
Huh?
February 17th, 2009 at 1:23 PM
I say bearings aren’t necessary because all you’re ever going to do is spin the thing one half or one and one half revolutions in a day or two every few weeks. In my mind the key would be to have positive “stop” positions that can be locked out in the bench once the tools are upright in the working position.
Here’s the trick to balancing the different load/weight of the sliding miter saw versus the drycut and the grinder…ready?
Offset the shaft/axle away from the center line toward the heavier components i.e. move it toward the side of the deck where the drycut and the grinder will live.
You can do this in the garage floor by taking the plywood deck you want to use, put the fence post pipe under it, tack the tools (saws and grinder in their approximate positions with sheetrock screws and move the post around underneath like a kid’s “teeter totter” until you get close to balanceing.
Then clamp everything down with U-bolts or whatever and move the miter saw to the opposite side of the second deck you add–being careful that your wood distribution added is uniform and you got a home made version of a “flexible tooling station.”
February 17th, 2009 at 1:34 PM
Scuse me, I thought it was obvious, but I realize I was being obscure.
Not a lazy susan bearing (I think they’re called racetrack bearings actually?); 2 large ring bearings, two pedestals; one on each side.
It significantly reduces the torsional and balance problems of having an axle, and allows for better and more useful tabletop construction.
Probably considerably more expensive though.
February 17th, 2009 at 2:05 PM
Leo’s trying to figure how to do it with a Bobcat.
February 17th, 2009 at 3:04 PM
🙂
February 17th, 2009 at 6:36 PM
“Leo’s trying to figure how to do it with a Bobcat.”
🙂
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Does a Bobcat have a PTO?
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I can think of possibilities if so…
February 18th, 2009 at 12:54 AM
After reading both the post and the comments, I’m THOROUGHLY
confused.
How about a sketch of what you have in mind?
Thanks!