How is caster load bearing capacity calculated?

sonambulo

Diamond Member
Feb 22, 2004
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I'm building a desk out of pipe that will have four expanding stem casters, one in each corner post. Each caster is rated at 180 pounds load capacity.

If I put all four casters on does that mean I have a total load capacity of 180 pounds or 720 pounds?
 

KMc

Golden Member
Jan 26, 2007
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Technically, but that means all of them will be at, or potentially exceeding capacity depending on the weight distribution of the desk. Not much safety margin in that setup. Plus, I'm assuming you are going to put things on and in the desk, so you need to account for that as well.
 

PottedMeat

Lifer
Apr 17, 2002
12,365
475
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this says 720 - but as said above think about the distribution

http://www.shepherdcasters.com/caster-basics.html

Divide the load capacity needed by the number of casters your product will be using. For example, your cart will need to carry 600 pounds and will use 4 casters: 600 pounds / 4 casters = 150 pound load per caster would be sufficient for your cart.


heh never seen those expanding stem things before, usually i just weld a threaded nut in the tube
 

sonambulo

Diamond Member
Feb 22, 2004
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Unfortunately I can't weld. I was thinking about buying some plugs and tapping them but my gut is telling me they won't be particularly sturdy. I'm looking at approximately 200 pounds of pipe/butcher block resting on those wheels so I want this to be sturdy as hell.

I'm thinking that load capacity in fact is multiplied by caster. Think of staging, circ saw benches on (tiny) wheels, etc. I just want to be sure before I buy all the parts.
 

Miramonti

Lifer
Aug 26, 2000
28,651
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Well it obviously comes down to how the weight is distributed.

Yep, have to account for a little rocking as well seeing they are on wheels. If when it's built, these wheels don't roll easily, a shift in weight could put some force at a slight angle and not always on the casters directly top to bottom, where the rating is be designed to account for.
 

Miramonti

Lifer
Aug 26, 2000
28,651
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Well it obviously comes down to how the weight is distributed.

Yep, have to account for a little rocking as well seeing the weight is on wheels. If when it's built, these wheels don't roll easily (depending on surface etc.), a shift in weight could put some force at a slight angle and not always on the casters directly top to bottom, where the rating is be designed to account for.
 

sonambulo

Diamond Member
Feb 22, 2004
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Well it obviously comes down to how the weight is distributed.

The 200 noted above is distributed evenly across the structure. It's basically a box with the bench top laid across it.

I'm approximating 100 loads max on the top bench spread pretty evenly plus about 50-75 on the bottom shelf also spread evenly.
 

SphinxnihpS

Diamond Member
Feb 17, 2005
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You have to look at the weight these things MAY bear at any point in time. The problem is that I do not know if the 180lb figure is the failure weight limit of the caster, or weight limit for proper operation of the bearings in the caster. If the 180lbs is the failure point of the caster, I would get bigger.
 

sonambulo

Diamond Member
Feb 22, 2004
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I'm looking at another set rated for 280. That's about the heaviest I can find expandable.
 

3chordcharlie

Diamond Member
Mar 30, 2004
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The 200 noted above is distributed evenly across the structure. It's basically a box with the bench top laid across it.

I'm approximating 100 loads max on the top bench spread pretty evenly plus about 50-75 on the bottom shelf also spread evenly.
Don't forget that someone is going to stand on this desk at some point, and there's a good chance they will weigh more than 150-175.
 

twinrider1

Diamond Member
Sep 28, 2003
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720. Not that I'd push it all the way to 720, but those should be fine under normal use...even a normal sized person standing on top.
 

edro

Lifer
Apr 5, 2002
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Load capacities are always very safe to begin with. Your safety margin is already built in.
Go ahead and build right up to 720lbs.
 

dmw16

Diamond Member
Nov 12, 2000
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As others have pointed out it is a function of weight distribution. It's a pretty simple statics problem to solve.

I would agree that you should use the strongest ones that will work within your design constraints but you can keep in mind that the casters themselves have a factor of safety designed into them as well.

How heavy of a desk (with stuff on it) are you expecting to have?