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  #1  
Old 06-08-2007, 04:40 AM
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Weight limit on casters.

May sound like a dumb question but say a caster has a weight limit of say 125 lbs. If 4 are used on a rolling tool cabinet does it mean the weight limit of the cabinet is now 500 lbs? HF has the 3 inch light duty casters on sale for 1.99. I asked one of the people at the store to confirm and they said that if 4 casters are used the weight limit is increased 4 fold but they didn't seem to confident with their answer. Just wanted to confirm with the board.
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Old 06-08-2007, 07:21 AM
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In theory that is right, assuming the load is evenly distributed. The problem is that the HF casters, as well as the ones sold in the box stores, are nowhere neare the rated capacity in performance. The frame/wheel will hold the load but the axles and bearings are substandard and will bind when rolling or turning (for swivel casters).
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Old 06-08-2007, 09:14 AM
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Another factor is that if you have an uneven floor, the total load may at times be supported by as few as two casters. This will be brief, as the cabinet rocks around, but having one caster off the floor almost continuously, so that the load is carried by only three, can occur quite easily.
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Old 06-08-2007, 10:21 AM
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I built a rolling sheet goods rack with 4" casters from HF, and two of them (casters) subsequently failed on me-the axles tore out. I will not buy any more of those from HF, next time I will spend the extra and get good functional ones from one of the online sources.

Paul
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Old 06-08-2007, 10:44 AM
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Quote:
Originally Posted by LarryG View Post
Another factor is that if you have an uneven floor, the total load may at times be supported by as few as two casters. This will be brief, as the cabinet rocks around, but having one caster off the floor almost continuously, so that the load is carried by only three, can occur quite easily.

This is a very valid point.
I'll go farther and say a lot has to do with weight distribution. If you distribute the weight evenly and the unit is stiff enough so it does not "conform" to the contour of the floor, then the so-called center of gravity (CG) is centered and the unit acts as if all the mass were concentrated there.
So in the case where a four-wheeled item is on an uneven floor, the vast majority of the weight is actually carried by two casters, not three. And this condition is not brief, but more or less continuous. The weight on the third, side caster is only a tiny fraction goverened specificially by the amount by which the true CG missed the center-line drawn between the two casters bearing most of the load.

The only time three of four casters would share the load equally would be when the load center is off-center of the cart and geometrically between the three casters.

So, it's also possible that the entire load of the cart will be on one wheel, this happens if the CG is over one corner. This might happen when, for example you sit on one corner of the cart. But its not likely to be a normal condition as the cart would be on the verge of tipping over, it would be virtually unstable.

I think it would not be unwise to choose casters so that each could carry at least 60-75% of the total weight, this allows for dynamic loading such as where you push it and the leading caster encounters a small bump. In addition the rolling and swivelling performance will degrade as you approach the load limit, being conservative preserves the easy-rolling/steering you would want. That means, for a 500 lb. total load, I would choose casters rated for 300-375 lbs each. That's way more conservative, than dividing the load equally (125 lbs per caster), but I hope I explained why.
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Last edited by LCHIEN; 06-08-2007 at 11:48 AM.
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Old 06-08-2007, 11:03 AM
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I think Loring is on target as usual. I think the common rule of thumb is to not exceed the total weight limit of three of your four casters. A 300 lb load would need 4 casters rated at 100lbs each.If your floor is rough or uneven, I would go up in size before I would increase capacity although they usually go hand in hand.
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Old 06-08-2007, 03:54 PM
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I personally don't like going over what two caster can hold, on most things. Things always seem to weigh more than what you think, you seem to stuff more things in them down the road than what you first planned them for, larger margin of safety.
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Old 06-08-2007, 04:18 PM
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Build carts with three casters, then? Each has to be 33% beefier, but there will never be a time when all three aren't on the ground?
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Old 06-08-2007, 04:39 PM
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Quote:
Originally Posted by cgallery View Post
Build carts with three casters, then? Each has to be 33% beefier, but there will never be a time when all three aren't on the ground?
Stability is much less, though.
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Old 06-08-2007, 06:45 PM
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Quote:
Originally Posted by LCHIEN View Post
Stability is much less, though.
Good point. I suppose you could have some "emergency casters" in the corners that are (for example) 1/4" higher than the center caster. They could provide some extra stability in the event that the unit starts to come over. Not very elegant, though.

How about four caster independent suspension?
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