Please help me resolve this head scratching DIY math problem...

[MetroMan]

Hey guys, I'm moving into Lofts399 at the end of the month and I'm going to use my place as a photo studio regularly. While figuring out my layout and furniture, I've come up with a scheme that will allow me to simply push the couch in a straight line into the bedroom and then hook a cross bar for my backdrop, set up lights and voilá, I have a large open studio.

I've run into one problem however. In searching for locking casters for my couch, I've found that they of course have weight limits. None of the casters in the 4" size I need supports more than 225 lbs.

Now, math has never been one of my fortes but I understand that that weight limit is for each caster. If all the weight of the couch and the people on it were bared by a single caster, it would certainly break. Since the couch has 4 casters, would the weight limit increase to 900lbs? I know that depending on where people are sitting on the couch, some casters will be stressed more. But will 3 average people on a couch weighing about 100lbs exceed the breaking point of any one caster?

I figure this is a problem for a math wiz to use a formula against. Any takers?

 

[MetroMan]

I don't mean to reply to my own thread but here's my thought process so far to get a discussion going:

I've determined that the load from the couch is stable since the casters are always in the same place. The back ones probably bare more weight since there is more couch on the back than on the front but for simplicity's sake, let's say that the 100lb couch puts an equal load on each caster. So that's 25lbs per caster. They have 200lbs of weight capacity remaining.

Now, if a 200lb person sits right in the middle, their weight divided by the 4 casters is 50lbs. There's 150lbs left per caster. If another 200lb person sits on the right seat, it's fair to say that most of their weight is born by the 2 right casters. Let's go with 3/4s of their weight, or 150lbs, divided by the 2 right casters, so 75lbs each, leaving each caster with 75lbs of load baring left. The remaining 50lbs is born by the casters on the other side, so that's 25lbs each. That's 125lbs remaining on the left side casters. Now somebody weighing 200lbs sits on the left so the previous calculations are mirrored, putting 75lbs on each of the left casters, and 25lbs on each on the right.

That leaves us with 50lbs remaining load baring capacity on each of the 4 casters. That's a safe tolerance I guess? I don't weigh 200lbs and I don't think many people in my group of potential guests does either, so I should be safe right?

... or am I totally wrong and this is much more complex than this?

 

[Admiral Beez]

I'm in the construction and home improvement products trade, and we always have a 4:1 safety ratio. I imagine the same goes for casters, so if it's rated for 225 lbs. you can be sure it's ultimate failure load is closer to 900 lbs each. if you look at the casters you have, if the tops and sides are metal, I am certain you couldn't possibly break them - in this case the failure would occur at the wheel or axle, but since the sides and top of the caster are metal, I'd say the wheel and axle are tough too.

Here's the caster you want http://www.homedepot.ca/product/3-inch-general-duty-swivel-casters/959444. Here's an assortment http://www.homedepot.ca/webapp/wcs/...atchallpartial&Dx=mode+matchallpartial&s=true Just stay away from the ones with plastic sides and tops and you'll be fine with your couch no matter how heavy or off centre your visitor.

 

[MetroMan]

Thanks Admiral Beez.