Weighty question

If a caster with wheel is rated at 330 pounds, would a four-wheel base be rated at 330 or 1320 pounds? I need to build a mobile base with four braked caster wheels for my new lathe and plan to use around 500 lbs of sandbags in the cabinet to eliminate vibration.
TIA
Larry
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Gramp's shop wrote:

That is correct - if weight is distributed evenly.
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Michael Joel



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Michael Joel wrote:

Mis-read. 1320#.
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Michael Joel



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In typed:

And it's always on perfectly level floors. There's something very wrong if you need all that weight to dampen vibrations.
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1320, assuming: a) the weight is evenly distributed across all four wheels b) the frame is capable of bearing that load c) you really want to load the casters to their rated limit
If the weight is not evenly distributed -- which is likely to be the case with a lathe, since the headstock, motor, drive assembly, etc. are all at one end -- then less, in proportion to the distribution.
Suppose, for instance, that 60% of the weight is at one end, and 40% at the other. No two wheels can bear more than 660 pounds, so at the heavy end, 660 pounds = 60% of the total, so the maximum that can be supported is 1100 pounds, 660 on one pair and 440 on the other.

You could, of course, adjust the sandbags as needed to produce an even distribution.
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Doug Miller wrote:

Mathematically correct. The casters, however, probably have a fudge-factor built in. They may actually stand a 10% increase over their rated capacity, or 50%, or even 200%.
Larger wheels/casters will bear a greater load (usually) plus make the thing even more mobile.
The OP is likely okay, but, nevertheless, he should keep his toes from under the thing.
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On 3/6/2012 6:08 AM, HeyBub wrote:

Unless made in China, then the fudge factor may work the other way.
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On 3/6/2012 6:36 AM, Leon wrote:

No shit! ... LOL
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I sure wouldn't push the specs of a caster, US or Chiwanese. It doesn't pay.
-- Learning to ignore things is one of the great paths to inner peace. -- Robert J. Sawyer
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Correction: they are *supposed to* stand such increases over their rated capacity. If the casters under discussion are those available for a few bucks at Horrible Fright, I think it's something of an open question whether their actual load-bearing capacity even reaches that on the label, let alone exceeds it by some presumed but unspecified -- and unknown -- margin of safety.
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On 3/6/2012 7:38 AM, Doug Miller wrote:

There is ample evidence to suggest that, from drywall to baby formula, there is no word for "safety" in Chinese, at least when it concerns exports.
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Mathematically correct. The casters, however, probably have a fudge-factor built in. They may actually stand a 10% increase over their rated capacity, or 50%, or even 200%.
Larger wheels/casters will bear a greater load (usually) plus make the thing even more mobile.
The OP is likely okay, but, nevertheless, he should keep his toes from under the thing. ********************************** I second the larger wheel size comment. The bigger they are, the less problem there will be getting over some strips of wood or sawdust, or cracks and bumps in the floor. There always are some things in the way, unless you carefully sweep just before you move the unit.
Also, I aim at no more than 50% of the rated load on the wheels. It will move much more easily than a unit right at the wheel's load maximum.
-- Jim in NC
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On 3/5/2012 9:10 PM, Doug Miller wrote:

While the 1320# may be correct for a static load, I think the vibration will cause a faster deterioration of the castors, thus decreasing the load they will support.
Have you considered other methods of damping the vibration such as springs, rubber shims, etc. ie placing the lath on a secondary top and supporting the secondary top with the dampening system.
While not the weight you are looking at, I find that my grinder sounds better and I can keep thing on the bench, when I place rubber shims between it and the work bench.
I have a workbench that is a 30" X 52", it has a shelf and small cabinets at each end. The base and the top perimeter is made out of 2X4 with half lap joints. I suspect the average weigh on the wheels is a little over 400#. (Lots of tools, other junk, and there is a lot of space to fill.)
I used castors with about a 300 pound rating. With a static load, these castors served me well for about 15 years. When they died the rubber split radially and basically fill apart.
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wrote:

All caster ratings I've seen are by the wheel, so 1320 is your figure.
-- Learning to ignore things is one of the great paths to inner peace. -- Robert J. Sawyer
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All the suggestions you have received about wheel rating apply as well as the non-uniformity of the load.
Here is another consideration: When moving the lathe on an uneven floor (even a little uneven) there will be times when only three wheels support the load and , Murphy's law, it is only one wheel on the heavy end.
Good luck,
Bill
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On 3/6/2012 9:20 AM, Bill Leonhardt wrote:

and the stand about 40. Adding about 300 pounds of sandbags for some added stability. 1,320 lb aggregate capacity ought to serve me well.
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On Mon, 5 Mar 2012 18:44:04 -0700, Gramp's shop wrote

You need to design for only two of the casters carrying the load (think uneven floor). Three points define a plane, but when the load toggles between two of the four wheels, the other two will be carrying 100% of the load (although this condition is very transitory). Most of the stress will be applied when you are wheeling the lathe around.
-BR
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On 3/5/2012 8:44 PM, Gramp's shop wrote:

What everyone else said, but I would build a cabinet with drawers and such and weigh it down with tools and whatever. My shop has no room for sand bags.
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Jack
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