Okay all you mechanical engineers ...


... answer me this question. If a caster wheel is rated at a load carrying capacity (which it is) how is the rating determined? I have a 600# tool I want to put on casters. Does each caster have to be rated at 600# or can I get four casters, one on each corner, that are each rated at 150# (or more) load bearing capacity?
This is important because casters with higher load bearing capacity are much larger and I want to keep the added height of the tool down to the bare minimum. Thanks all for your answers ...
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150# casters will work fine.
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Doug Miller (alphageek at milmac dot com)
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DIYGUY wrote:

Hello... Amateur here, but my thinking is you're going to have to go with a caster that's rated for the 600 #'s because of the weight effecting it when moving or shifting your tool.
Two thoughts.....If you have four casters (and I could be out in left field here) that are rated for 150 # each and move the machine laterally and hit a crack in the floor or something that stops the wheels you have now transferred the load onto two of the four wheels, which would be doubling their load from 150 #to 300 #. My other thought is that even though the load is spread among four casters it's still 600 #'s pressing down on all four of them.
Usually the load rating on a caster is a bit understated, so you might be able to get away with 300 # rated casters.
Just my offerings (or ramblings depending on your view).........
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If the floor isn't flat, the load can shift to two of the wheels. If you move the tool fast enough, you could get it up on one wheel on an uneven floor, but that's pretty extreme.
I wouldn't go with anything less than 300lb capacity. If the machine is not nice and symmetric, the load will be to one side and the capacity would need to higher than 300lb.
You'll also have to add the weight of what's on the machine if it is used with casters in place.
Mike
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I would go with four 200# casters
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DIYGUY wrote:

Strictly depends on the load balance...if it is a uniform load, the weight is shared equally by all four. (To visualize, think of you standing up straight, weight on both feet--each is half your total. Now slouch and put your weight on the one--it's carrying essentially the whole load.)
I'd oversize by some, even though there will be a safety factor in the design (unless they're a really, really cheap import and then I wouldn't trust the rating, anyway) primarily because the heavier ones will roll easier if they're not at the load range limit and the installation will just feel more solid.
Someone else suggested 200#/ea--that would be a good target methinks.
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Well, we could get into center-of-gravity calculations and draw free-body diagrams. But I don't think that's what you asked. :-)
Most of the answers given already are correct. Its a valid engineering approximation to divide 600 lb across the four wheels for most stationary tools. However, don't just use the weight as a factor. Caster material and minimum caster diameter are just as important. You can get a lot of casters that will do the minimum load of 150#, but I sure wouldn't put a stationary tool on 2 inch soft neoprene casters. For one thing, cheap soft casters will tend to get flat spots holding up a heavy stationary machine. I'd say you probably should not have anything less than 3 inch diameter wheels. Go with industrial grade casters, too. That rules out most of the things you find in Lowe's.
For a retail outlet source, I think the heavy duty casters sold by Woodcraft are more along the lines of what you would be looking for.
When you calculate height, remember to look at the actual height of the overall caster, not the nominal diameter of the wheel.
Bob
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DIYGUY wrote:

If you have a Northern Tool in you area, they have a pretty good selection of casters.
Tom
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It occured to me that we all focused on answering your question about casters. I was thinking.. It sounds like you are contemplating putting the machine right on top of the casters. Virtually all the machine stands I've seen have the casters mounted outside the legs of the machine, so the machine can sit as low as possible. Height of the caster should not be major factor. Also, for a stationary machine that weighs 600 pounds, I would think you should use metal construction. You will be hard presssed to build your own out of metal and save any money as compared to buying a commercially built stand.
Bob.
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Load factor is one thing. Yes, the 150# caster is able to take the total load of 600# assuming equal distribution.
Size is a whole 'nuther factor. I'd not use less that a 4" caster for a tool stand. To put this into perspective, go out to the curb in front of your house. What will go over the curb easier, the 27" wheel of a bicycle or the 6" wheel of a baby carriage? Smaller wheels are more likely to get hung up on a wood chip than a larger wheel.
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Go to mcMaster Carr http://www.mcmaster.com /
They have 1001 casters in 200 to 600 lb range. Everything you ever wanted to know about casters are described there.
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how smooth is your floor?
think about where the weight goes when one wheel hits a bump.
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DIYGUY (in snipped-for-privacy@g14g2000cwa.googlegroups.com) said:
| ... answer me this question. If a caster wheel is rated at a load | carrying capacity (which it is) how is the rating determined? I | have a 600# tool I want to put on casters. Does each caster have | to be rated at 600# or can I get four casters, one on each corner, | that are each rated at 150# (or more) load bearing capacity? | | This is important because casters with higher load bearing capacity | are much larger and I want to keep the added height of the tool | down to the bare minimum. Thanks all for your answers ...
I have a 75# shop cart with four 150# rated casters from my local lumberyard. I loaded a 90# panel (gently) onto the cart and pushed it across the shop - crossing two joints in the concrete floor. Two of the caster wheels failed.
Right now I'm thinking about plastic-tired steel wheels with a minimum rating of 600#.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto/solar.html
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