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I need castors for a kitchen island. I need to know what to get. Do all the castors need to carry full weight or do I divide by 4 to get say 4 50lb to hold a 200lb cabinet for example?

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    Hello, and welcome to Home Improvement. Would you add a picture of the island in question? And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Oct 3 at 11:10
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    There are more important factors such as : Will steel casters damage the floor, 2- Will polymer/rubber casters get a flat spot on the bottom sitting in one position, 3- Is the diameter large enough to permit easy rolling ( the smaller the roller , the smaller a particle that can stop it.) 4-.Do you want to move it a few inches or do you want to roll it to the next room ? – blacksmith37 Oct 3 at 15:41
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    @blacksmith37 excellent thoughts. Also whether the island will stay on the casters permanently or if there are weight-bearing jackscrews that can be lowered, like a refrigerator or some workshop-casters, to take weight off the round part and the axle. – Criggie Oct 4 at 1:31
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    Don't limit yourself to using 4 castors. 6 or 8 might fit your needs better than 4. – Dotes Oct 4 at 1:36
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    Will you ever pound meat on the table? That can have a sharp force increase on it – user2813274 Oct 4 at 10:22
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When buying castors, they're generally marketed as a set that can carry a total load. ie a set of 4 '200 lb' castors are meant for an object that weighs under 200 lbs.

I'd simplify your problem by estimating then doubling that. If an average person can lift 50 lbs, is the kitchen island something 2 people can lift? Get a set of 200 lb castors.

Would it take 4 people? Get 400 lb castors.

The difference in cost of castors is small enough that I might just get 1000 lb castors and call it a day.

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    Yes, double it. By the time you load down the island with pots, pans, food prep, a leaning person, etc, you can easily overload castors that are rated for just the "empty weight" alone. Paying more for better castors now prevents having to buy them later, along with the trouble of reinstalling them. – computercarguy Oct 3 at 18:58
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    Your four casters had better be able to support a 200lb cabinet and a 300lb man.... and then a safety factor of at least 2, so double that. And here we are at 1000lbs. +1 – Mazura Oct 4 at 1:06
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    If it's an island, someone will sit on it or stand on it at some point. I'd do 1000 pounds at a minimum, just for piece of mind. – Eric Hauenstein Oct 4 at 13:05
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    @EricHauenstein You will also want the locking wheels. – Dan D. Oct 4 at 14:01
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    You don't want to refuse spontaneous kitchen-table sex because you got the cheap castors. – dotancohen Oct 5 at 19:18
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How to weigh the kitchen island:

  • Get four bathroom scales. You almost certainly have one already; borrow the rest from friends.
  • Position the scales under the island in the (approximate) position that you intend to fit the castors. You may need to place blocks of wood on the scales so that the island doesn't hide the dial.
  • Read the weight that each castor needs to support off the scale.

At this point I would be very generous with the rating of the castors (stronger castors are not that much more expensive, and if one breaks it will be a real pain). - Certainly use the highest load for all four castors - Allow for the "stuff" you are going to put on the island (and in it if it has drawers) - Allow for a heavy man standing on one corner of the island (assume the castor they are standing over will have to take all their weight).

P.S. Sorry for your loss.

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    Minor improvement - instead of four scales, use blocks of wood the thickness of the scale in the other three positions, then rotate the scale between each position, measuring the weight at each point. Or, if the island is relatively symmetric, one position is probably enough. – tilde Oct 3 at 15:39
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    @tilde, a typical bathroom scale flexes as you weight it. Even if it does flex, a box supported on 3 corners with blocks will have a unpredictable balance point so you can't really determine how much weight should be on that 4th corner. – JPhi1618 Oct 3 at 17:57
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    4 measurement points with blocks won't work, it will cause measurement errors. The most measurement points you could have using that method is 3. However the least you can have for stability is 3, so it has to be 3. – Harper - Reinstate Monica Oct 3 at 18:03
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    @MartinBonner Yes, 3 blocks + 1 scale is a fail, for the reason it's possible for 4-foot things to wobble. 2 blocks + 1 scale can work if the measurement points are kept identical. – Harper - Reinstate Monica Oct 3 at 20:14
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    @tilde Great Idea. However, I would simple prop the two corners on the far end of the cabinet. Then set the scale under the middle of the other end of the cabinet. By definition this will weigh 1/2 the weight of the entire cabinet. I'm assuming the scale is centered under the center of of it's end of the cabinet. However, you only have the weight of the cabinet, please note Harpers point below. – Robert Cline Oct 4 at 23:51
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The problem is that your castors not only have static forces, they also have load forces (someone sitting on it) and dynamic forces of rolling it around.

If you've ever pushed a rolling cabinet around, you've experienced the "THUD" when it suddenly hits something and stops abruptly. That creates dynamic forces on the cabinet that can be even more than the static loads.

So you need to upsize by several factors, e.g a factor of 3-4.

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