How to determine the size steel I need to support a given weight

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I know I dont know something and need some advice please.I am a self taught person who happens to own a welding machine.  Need to create a 4'x8' frame that will support roughly 3000 pounds thats on casters.I have three questions...Can someone give me advice on what size steel I should use to support the weightHow many casters should be under this frame?Can anyone point me to a chart or such that I should have been able to easily locate had I know what I was looking for here so I dont have to post noob questions.(Just cause I am doesnt mean I have to act this way)I would look this up if I new where to look.Thanks in advance.Hobart Handler 140Longevity LP-40D Plasma Cutter14" chop saw4.5" angle grinder
Reply:The thickness and type of steel used depends on the design.  Can you post some drawings of what you are doing?  Design is very important.  How high up will this frame have to stand?  How many legs are coming down to the floor?  How well are you able to triangulate the frame?  Really, without drawings, there is too much information needed to just give a material type and thickness...Esab TradeMaster TorchSmith AW1A Airline TorchLincoln AC/DC 225/125Millermatic 252 w/ Spoolmatic 15aThermal Arc 190 GTSSpeedGlas 9100v
Reply:From where i am at, I dont have a good way to post a drawing but its pretty basic design.Its a 4'x8' wooden box that will have all sorts of dividers in it and will hold roughly 36 cases of paper. (360 compartments that each hold 500 sheets) I just need to support this box, it needs to be movable (though it will mainly be stationary so no handles are required) and my lips on the side cant interfere with the bottom compartments so the lip needs to be 1/2 inch and i could go up the corners.So I am thinking of a shape like this (sorry for the crudeness) with 1/2 inch lips and 1/2x1/2 inch angle up the corners.  Not sure if this is best practice and not sure about what size to use?  Hope this clarifies?____________|     |      |       |---------------------Noticed after posting that the cross beams are not spaced out...In my post those 4 lines are spaced evening end to end length wiseLast edited by mtrammel; 10-02-2009 at 10:56 AM.Reason: clarificationHobart Handler 140Longevity LP-40D Plasma Cutter14" chop saw4.5" angle grinder
Reply:Sounds like I-beam would be a good choice for the main frame.   To know the size I-beam needed, you would need to do the engineering calcs for a load of so many lbs spread evenly along the beam over the distance between the castors.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:The "cart" does not need to be built from I-beamsthe 3000lbs will be spread out over the Cart/BaseCheck out this cart 4400lbs Capacity.http://www.northerntool.com/webapp/w...Product%20PageWith your base being 8' long you'll need a set of casters in the middleLast edited by Broccoli1; 10-02-2009 at 12:48 PM.Ed Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:Thanks to all.  I was following DesertRider33's post and learned about deflection.  That appears to be the key.  I will follow Broccolis suggestion for the extra casters.  I'm looking at something like http://www.anytimeproducts.com/meg/dollysteel.htm from 1/4 angle with extra cross members and casters.Really appreciate the input.  I hadnt dealt with this much weight before so figured I'd best ask.Hobart Handler 140Longevity LP-40D Plasma Cutter14" chop saw4.5" angle grinder
Reply:The success of your project depends more than you realize on the quality of the casters you use.   It seems easier to me to spec the design and size of steel for the frame than for the casters upon which your ton-and-a-half creation will rest. Don't buy cheap imported casters.  Remember, sometimes a cart or dolly will rest on just two casters depending on the contour of the floor over which it rolls.ScottMiller XMT 350 CC/CV w/gas solenoid opt.Miller S-22A wirefeederBernard 400A "Q" gunMiller Spoolmatic 30A / WC-24C-K 200A torch/gas lensWeldcraft WC-18 watercooled torchHypertherm Powermax 30Victor O/A
Reply:I have a habit to over engineer these jobs, They don,t brake and everbody is happy. I'm thinking of 2" x 6" rhs 3/16 wall with bracing. or RSJ 3" x 5" with 1/4" web thickness and bracing.This is just a rough guess.  If all else fails there is a fomula, but I have no idea of how to do it.http://en.wikipedia.org/wiki/Second_moment_of_areaIMO RHS is easier to work with.
Reply:Thanks to all...they finally pulled the trigger and heres the final dollyAppreciate all the help!PS...used Fairbanks castersHobart Handler 140Longevity LP-40D Plasma Cutter14" chop saw4.5" angle grinder
Reply:Looks good!  Glad you got the job!MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Careful!  Would guess your casters are significantly undersized for 3000 pounds. I estimate those are 2 inch casters and have a load capacity of perhaps 200 pounds maximum each. With deflection (a simple beam), you can expect the center casters to each support more than 1/6 (500 pound each) of the total load.  It appears the center casters are non-swivel, the left end as shown are swivel, but cannot confirm the type of caster on the right end.  Appears your frame is 2x8 instead of 4x8 but looks can be deceiving.  As a minimum I would use higher capacity casters and add one on the cross bar between the two center casters to compensate for the higher center loading.
Reply:Did anyone look at this gasoline torch!!! imagine strapping that thing to your back!
Reply:Originally Posted by mtrammelIts a 4'x8' wooden box that will have all sorts of dividers in it and will hold roughly 36 cases of paper.