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?
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.
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.
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.