calculating metal size/selection?

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I weld up mobile bases for my woodworking tools and they weigh from 400-600 pounds.  The base of the tool is aorund 20" x 20" and only requires support around the perimiter.  My current design is shown below, it uses 2" angle iron that is 1/4" thick.  They work great and are solid, but the metal is heavy and expensive.  How can I calculate how thin I can go?  I am now wondering if 1/8" x 2" angle iron would be sufficient.  I know, for example, that bed frame rails (1.25" x 1/8" thick angle iron) isn't stiff enough.Chris
Reply:Hello *chris*.                  Nice job, as regards material for that sort of weight I would stick with the 1/4" thick angle, For a little extra strength and stifness I would also weld triangular gusset plates to the wheel carrier plates Cheers  Gordon.
Reply:Originally Posted by gordon stephensonHello *chris*.                  I would also weld triangular gusset plates to the wheel carrier plates Cheers  Gordon.
Reply:Hi  *chris*              Some other members will be able to help you out with calculations etc,  rule of thumb I would recon the same 2"x2"x1/4"angle with modified strengthened wheel arranement will be O.K .  Cheers  Gordon.
Reply:Nice looking bases Chris.  I think what Gorden is getting at is to weld some triangles to the inside corners under where the corners come together to add a bunch of strength.  You might want to go with some heavier angle iron for the caster mounts and heavier casters for the 2000 pound model.Bob from Idaho
Reply:Very good job on the base. For something like 2000# I would find casters that would support a little more than the load. For example, four 600# casters. Then I would make the mounting tabs large enough for the casters to rotate 360 degrees with enough stickout on each side to add a triangular gusset on each side of the tab. The size of the metal for the frame will depend on the length of each frame member. Without knowing the size of the base that holds the 2000# object I wouldn't know what to recommend.Last edited by Oldtimer; 11-11-2008 at 11:00 AM.
Reply:I saw a project on another site where the guy built a base for a Bridgeport.  I'll try to find the pics and post them.  I remember it being pretty beefy with good bracing at the casters."Any day above ground is a good day"http://www.farmersamm.com/
Reply:This is a perfect example of using Solidworks with its built in load calculation software. We typically do these types of projects that allow us to build frames and supports then apply a load to it in many directions to simulate a load. it will then show us the areas of weakness. So if you apply a load of 200-400 lbs and want to see what happens when you push the cart around loaded, you can see the effects of your welds, along with the members such as gussets, brackets, angles related to the frame. You can also put in minimum deflections you wish to attain so that skinnying up a frame will allow you to see where it will bend with or without additional stiffening.this is why it was developed for use in solidworks! But it is not a cheap program. Your best is to find someone who will design you a frame, based off of your parameters, and have it tested. They can then give you exact cut lists and materials list to make the frames you want at a lesser cost using lighter materials.Good luck, that is why we choose to use this excellent software package.
Reply:For a machinery base you are looking for stiffness rather than strength - you could build it light but it would sag down to the ground before it failed.with the cantilever caster support you have the max deflection is going to be based on the moment load applied by the swivel distance for your caster times the load.  Say 500 lbs times 1.5 inches = 750 inlbsNow if it is mounted 3 inches from the welded base the maximum deflection would be 750*(3*3) divided by 2*young's modulus mulitplied by the moment of inertia.If you have a 1/4 by 2 inch flat bar the moment of inertia is .0208 so you would get .005 inchesMachinery's handbook has all this stuff but in general the farther your caster is from the base the stouter your mount will need to be.  500 lbs on a caster isn't really that much so you shouldn't need to get too much beefier.
Reply:Originally Posted by djburtonFor a machinery base you are looking for stiffness rather than strength - you could build it light but it would sag down to the ground before it failed.with the cantilever caster support you have the max deflection is going to be based on the moment load applied by the swivel distance for your caster times the load.  Say 500 lbs times 1.5 inches = 750 inlbsNow if it is mounted 3 inches from the welded base the maximum deflection would be 750*(3*3) divided by 2*young's modulus mulitplied by the moment of inertia.If you have a 1/4 by 2 inch flat bar the moment of inertia is .0208 so you would get .005 inchesMachinery's handbook has all this stuff but in general the farther your caster is from the base the stouter your mount will need to be.  500 lbs on a caster isn't really that much so you shouldn't need to get too much beefier.
Reply:Nothin like a good old delta!!
Reply:Hello *chris* Nice job with the caster base. I do the same thing in my shop as floor space is a priority. I was just wondering if the casters in the picture are swivel and/or brake lock type.I would think when you are using the machine it would want to move or roll. I know from my own experience that even my belt sander would move during use if I did not have locking casters.
Reply:Originally Posted by OMSHello *chris* Nice job with the caster base. I do the same thing in my shop as floor space is a priority. I was just wondering if the casters in the picture are swivel and/or brake lock type.I would think when you are using the machine it would want to move or roll. I know from my own experience that even my belt sander would move during use if I did not have locking casters.
Reply:Calculating the strength of a weld depends on the loading type. Welds perform different under different loads. --Gol'
Reply:why cantilever the casters...mount em direct under the corners .
Reply:Originally Posted by *chris*These are swivel type casters that have a foot that lowers to immobilize the caster.  I generally just drive a wooden wedge under the base to stabilize it as lowering the foot is cumbersome.http://www.greatlakescaster.com/products.php?cat=262onesource, I am doing this for fun, not profit so no budget for Solidworks.  Funny thing is my neighbor and one of my sons friends parent both work there djburton, how does this translate into square tube?  I am starting to think right now that 2" square 1/4" wall tube could hold the 2000 pounds.  How do you calculate the strength of a weld?Chris
Reply:that is not how you calculate the strength of a weld. When doing weld sizing calculations there are many factors to consider. For example if you have a cantilever beam that needs to be welded to a steel wall and the beam has to support a 1000lb load at the outer end. You have to figure out all of the forces acting on the beam such as the force due to bending, force due to vertical shear, twisting ect. Then you have to add them all up vectorically. Then there is a formula that is total force/force allowable. The force allowable is equal to .3xmaterials tensile strength. That is called the electrode way and for partial penetration welds such as fillet welds the filler will hold 30% of it's tensile strength under a shear load. Fillet welds break through the throut. there is alot more to calculating weld strength and size than just taking the filler strength and dividing it by the weld thickness. --Gol'
Reply:Yes Go1lum, I incorrectly split my response where I talked about the load, vertical, shear, etc. All these are the determining factors on a given weld, and the acceptable loads to be applied for given useage, etc. The basics of the welds absolute strength don't much change, the strength of the filler itself is what the label says; the use of the filler is the great question that defines the absolute maximum force one would want to apply to the weld.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Originally Posted by RojodiabloThe basics of the welds absolute strength don't much change, the strength of the filler itself is what the label says.
Reply:Hi Chris,   Nice job on all. To add strength to caster clips, add a reverse gusset, kinda like cables on a suspension bridge. From top outer edge of caster clip 45 up a few inches, parallel angle cross member 4 inches or so and 45 down to bottom of cross member..weld solid.Miller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180