engineering question

[paintandbodtman]

This may seem fairly simple to all the engineers on this site but here's the situation. I need to make 4 dollies, each dolly will be 12''-13" square made out of angle iron with 4 pivoting casters, these dollies need to be capable of supporting a minimun of 1/2 ton each. Am I correct in assuming that useing 4 casters rated at 300 lbs each will be sufficent or do I need to use a higher rated caster.
These will be used on a decent finished concrete floor, any particular type of caster that would be best.Need to stay around 4" in size on the casters because of height restrictions if at all possible, would be nice if I could stay in a moderate price range on the casters also. Any suggestions from anyone

Wayne

[Tom Miller]

I recall some discussion on this -- you might try the search to get answers (opinions ) faster. But, here are some points to ponder:

- Depending on how rigid the dolly is, and how uneven the floor is, there's a good chance that three of the four casters will be carrying the load at any one time.

- Depending on the weight distribution on the dolly, one or two casters may be carrying more than their fair share.

- Caster weight ratings should be taken with a grain of salt.

- The more generous the weight rating, the easier the dolly will move, in general.

Regards,
Tom

[TheRic]

I'll second Tom on all his points. I've been told that you should figure that at any given time 1 caster could have 60% of the weight.

[jackellis]

I just put a cabinet made of MDF on wheels that were rated for 75 pounds each. The whole thing probably weighs 150 pounds loaded. It does not move all that willingly.

Consider casters that can hold 500-600 lbs each.

[LCHIEN]

If its rocking on two wheels (one wheel higher than all the others) and
the load is not perfectly centered, than one wheel can carry way more than 50% of the entire load. THose guys suggesting each wheel be rated for >60% of the entire dolly load are probably right.

[Pappy]

Take a look thru the online listings here http://www.casters.com/catalog/index.htm then give Joe Mauro a call at 1 800 327-6353 ext 210.

The ratings, and quality, on their casters are better than the imports you see most places. Casters can also be set up with different style/size mountings the suit your application. Also, Joe is a woodworker and will work with you.

[jeff_1064]

When I worked for a concert lighting company I made a few "flight cases" or road cases for our equipment. Each case carried 1000 feet of 4/0 cable or 1000 feet of 3/4" wire rope (aircraft cable) or as many 5/8" shackles that we owned. I would say the boxes were loaded with at least 1/2 a ton or more. We used to roll these things everywhere... on grass, gravel, ice...you name it and we rolled on it.

When I built the cases they resembled an "Anvil Case"

http://www.anvilcase.com


Here is a link to the company that sells case hardware that I have used in the past...They have a lot of different casters.

http://www.penn-elcom.com/

Jeff

[dkhoward]

Firefighters rule of thumb

double the capacity and add ten percent for safety. . . .

[big tim]

What would concern me also would be the footprint of the dolly, 12" to 13" square is not much. How tall is the load? Would you push on the load or the dolly?

Tim

[JSCOOK]

I'm guessing that your going to use these dollies for moving a car/vehicle around on ... as in a body shop?

If so, I would assume that it would be possible for the load (tire) on an individual dolly could be off-centered and hence not evenly distributed to all four casters ... the size of the load footprint relative to the size of the dolly ... as well as mentioned all ready, two of the casters (diagonally across) could be a pivot point due to uneven floor or weld distortion in the dolly itself ... I'd take the safe route and assume that any given one caster could be asked to take 75% of the applied load ...

[paintandbodtman]

Thanks for the replies everbody.

Thom,ric,loring- all of your concerns are legit but don't think I'll have to be concerned that much with them
Pappy,jeff-good web sites will have to explore them a little more
tim- actually the footprint should be to my advantage as far as overrideing all of the concerns expressed by the rest
JSCook-pretty close on the usage, actually there will be a post assembly that sits in these dollies that have a clamp that fastens to the rocker panel pinch weld on a unibody or the frame on vehicle that has one under it, these assemblies will be tied together by square tubeing to form a square mounting jig that will be tied down stationary by pot sunk in the concrete floor when useing as a portable frame machine when not being used as pulling aperatus they could double as jig for moving restoration projects around hence the swivel casters on all corners. Every thing is 1/4 inch or thicker on all parts that make up these assemblies
and the dollies will be made out of 2" angle iron 1/4' thick with mitered corners and welded up in a jig by a local welding shop so squareness and warpage should'nt be a concern.
Every vehicle has what is referred to as the torsion box area which is basically the middle area between the wheels and usually unless the vehicle is t-boned in the door area want be damaged so the assemblies should be distributed fairly equal as far as weight is concerned.I actually had that backwards in that 1/2 ton would more than likely be the max load on each unit instead of minumum.
Sorry for the long winded post and thanks for the concerns and suggestions from everone,will more than likely will use either 300-400 lbs rated casters as wheel type is probably more critical than load rating in this instance.

Wayne

[MikeR]

Not certain if its germaine but when I re-rig a sailboat I always figure a 250% safety factor when determining the diameter of stainless steel cable which supports the mast.

Probably comparable safety factors in every profession.

Cheers,

MikeR

[wardprobst]

Hey Wayne,
Check these out-
http://www.amazon.com/Swivel-1000-Lb.../dp/B0000AWYMH
DP

[paintandbodtman]

Hey Wayne,
Check these out-
http://www.amazon.com/Swivel-1000-Lb.../dp/B0000AWYMH
DP

Thanks I'll have to check these out, maybe they have these at the retail store we have one about 30 min away. With shipping 22.00 shipping for 16 it might be worth the drive to the store plus can tell more about them in hand, at 1 1/2" wide they should roll pretty decent on good concrete.

wayne