True. I just wanted to establish the question of weight division. I was told by a cow-orker once (who claimed to be an expert on such things) that each caster would have to be able to support the entire weight of the item.
While it is sitting there static, each caster will be carrying 25 lbs of the load, maybe a bit more or less if it’s not balanced. However, I would put four 100 lb casters on it. If you are putting the thing into a u-haul, for example, and its rolling up/down the ramp and one of the casters catches on something, it could easily end up temporarily supporting most of the weight of the thing.
Seriously, you can’t go wrong by over-designing. As pointed out by engineer_comp_geek, there is dynamic as well as static loading to consider. Placing casters on an object implies that you intend to move it from time to time. Depending on the surface you move it over (wood, tile, carpet, asphalt etc.), the dynamic loads can be quite significant. Using a higher rated caster will (generally) make it easier to move and will also last considerably longer due to it’s heavier bearings.
The dynamic loads also include a shear force (opposing the direction of motion) to be accounted for. So regardless of the caster’s ability to bear weight, the method of attachment will need to be sturdy enough to prevent them from being ripped off during movement, i.e., 200 lb. casters won’t do any good if attached with 3/8" #4 wood screws.
Mr. Blue Sky didn’t specify what the piece of furniture would be, but you have to also allow for people or things that may perch upon it. Even a table, which you’d think of as not ever holding a person, will eventually have somebody sit or lean on it. If it’s a 200-lb. guy perching on one corner, then your load planning changes drastically.
If you recess the casters, allow for the wheels to sink into thick carpet; otherwise you’ll have a thing with wheels that won’t roll. I have such a thing in my living room. Also, allow enough room for the casters to swivel.
Or;
You could have the piece of furniture in the exact center of your house, and there could be a powerful earthquake, causing all the walls to fall away allowing the roof to fall and be supported by that piece of furniture…
not that I am actually good at building stuff, but if you’re planning on moving this peice around a lot, you might want to work in some extra bracing where the leg meets the body. My mom the piano tuner has repaired many an instrument because someone tried to move in on it’s little wheels and the leg ripped loose from the body. Just too much torque at the end of those long legs.
(PS. if you ever have to move a piano, never roll it! Rent a dolly or hire some guys to dead lift the thing, even it it’s an upright. The casters are decoration only!)
I thought you were talking about people who cast magical spells or wield the forces of magic. I’m glad you were not, as I was reluctant to give out any of the secrets from my grimoire.
Another thing to keep in mind is that it’s almost impossible to perfectly and equally balance the load amongst all four feet in a rigid structure. Most of the force will be supported by three of the feet, and the remaining foot will only support a small amount. At the very least, then, each foot should be able to support 1/3 the force.
But again, this assumes a very rigid structure. The less rigid it is, the more equally the force will be balanced across all four feet.
If this is something like a hassock or coffee table where it’s conceivable that someone might sit on it, plan on that someone sitting on just one corner, so one caster is carrying essentially all the weight of the person and your item. In this scenario, even a 100# caster wouldn’t be enough. Happily, casters for things like desk chairs are easy to find, and typically rated for 225# each or so.
Not to mention, lightweight casters just look flimsy and ARE flimsy. Snag one on a door threshold while moving this thing, and expect it to snap off.
Actually, the casters on our upright work quite well. However, the piano is so heavy, and the wheels so small, that in rolling the piano across the living room we left quite visible indented tracks across the hard wood!
I’m glad it worked for you (or almost worked), but I’ve seen both uprights and grands get their legs tweaked. Those people probably tried to move their pianos against carpet or some other complication. Since the repairs are expensive and ruin the main purpose of most pianos (decoration), standard advice is not to try it without proper equipment or a few beefy friends.
Sorry for the hyjack, just trying to spread valuable info, since all us dopers move pianos so very frequently.
Come on, Mr. Blue Sky, you’ve kept us in suspense long enough. Just what the hell are you building?
For furniture that gets moved only occasionally, using plastic “skid pads” instead of casters has advantages: cheaper, easier to mount, less obtrusive, less likely to leave marks in the floor, and easier to slide than you might think.