Welding table question/build

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Well, I finally got around to building a cart/welding table based on a 2x4" piece of 1/2" plate. I was inspired by a picture I saw here, but I cannot remember who posted it. I have everything figured out except the leveling feet to lock it down in place, and need to get the top plate. I made it 18" wide and 42" long (to allow 3" overhang on all sides) It seemed a bit narrow for my liking width wise, so I offset the legs on the bottom 1" making it 20"x42" long. Getting them square, and lined up with the bottom offset 1" was a bit of a challenge but thankfully a few pony clamps made it easy. I didn't take any pictures as I was building it but I will update with more pics tommorow.My question was, I built everything out of 2x2x.125" tube. The top is 18x42 with 14" wide "rungs' (3, plus the 2 ends). Factoring in a 1/2" thick top 24x48", with maybe 2 1" long welds per side, per rung, is this enough to keep it from bowing, as well as will the frame be able to hold, say, 1000lb on top? I realize this is dependent on the casters as well. My old table was real shaky with an engine on top of it.Here is the very dark, shaky picture as I completed it, test fit with a 1/4" top.Miller: 200dx, Bobcat 225, Passport, Powermax 45, Milwaukee: Dry Saw, MagDrill, grinders
Reply:Originally Posted by JohnR My old table was real shaky with an engine on top of it.
Reply:im building a table as well, i will get some pictures as soon as i get it put together.. what my plan is for leveling the table is to run the threaded extensions (basically a really long nut) inside my legs on the bottom weld them flush, drill holes and rosette them so it stays level. the feet are bolted to a .250" plate with a 3/4 is threaded rod welded to the plate with a jam nut so i can raise and lower as needed. the front 2 feet are locking swivel and the back 2 just swivel, i count find any fixed feet at the time. i guess i will find out this weekend how well it works.
Reply:Well, a local welding shop had some pretty nice EZ-Roll casters. Picked up 6x2 casters, 2 swivel w/ brake and 2 rigid no brakes for 100 out the door. They're steel rimmed polyurethane I believe, but they have a zerk on the axle, a zerk on the rim, and a zerk for the swivel. Very heavy duty. I'm thinking of outboarding them as you said DSW.No clue why it looks so wonky at that angle.I'll snap a picture of how I plan on outboarding the wheels. i don't mind if they stick out a bit all the time, I'd prefer it. No one wants a customer's engine or transmission to flop to it's (and your) doom because you hit a crack in the cement. The bottom is going to be loaded down with a toolbox and the sides will have pegboard like my first post. Do you guys think that so far, it will be able to support ~1k without too much flex? I can always gusset the corners if not, I suppose. And no, I don't plan on using only 3 wheels. It was just a mockup to see how tall it is vs the previous wheel I was going to use (shown on the right in the first picture). The height difference is what brings me to the outriggers as DSW suggested.Miller: 200dx, Bobcat 225, Passport, Powermax 45, Milwaukee: Dry Saw, MagDrill, grinders
Reply:For bending of the table top, I get about .04" deflection at the center with a 1 kip load at the center, with bending stresses in the longitudinal tubes of around 9 ksi.  Bending stress is based on the tubes alone, but for deflection I considered the stiffness of both the plate and the two tubes, but not welded to each other.  Stiffness would be improved somewhat if the plate was stitch-welded to the tubes.Stiffness against racking would be hugely improved with some sort of diaphragm in the sides (like the first one, but of steel), or X-bracing.  Or corner bracing.  It may not be necessary, and that could be checked just by putting a load on it and wiggling it, but the way it is, racking resistance is all through the welded joints and the stiffness of the tubes.In case anyone wants to check, I used a section modulus of .58 in^3, and moment of inertia of .58 in^4, with an unsupported length of 42", spans simply-supported.
Reply:Tkanzler. Thanks for doing the math for me. Think you can do it for me with a .25" top plate? I decided to use a thinner top plate after simulating how much it would weigh fully loaded with what I plan to haul on it, and it was a bit heavy for my liking. Decided to save some weight by going with .25" since this is just a simple welding / tool cart, and not my primary table. Having to haul a ~350lb cart down my driveway and up again isn't my idea of fun.Miller: 200dx, Bobcat 225, Passport, Powermax 45, Milwaukee: Dry Saw, MagDrill, grinders
Reply:I redit it, with 1/4" plate, but I considered the top welded (stitched, at least) to the longitudunal tubes so the top and the tubes act as a single composite beam.With a 1 kip line load across the top at mid-span, I get a max bending stress at mid-span of about 6.5 ksi.  For max deflection I get .017 in.Neither result includes bending the other way (modelled as a line load across the short dimension), but being narrow, it's not going to be much if it was a point load in the middle.That's assuming simply supported (no bending moment at the ends, which is not really the case), and enough weld to make the table top work as one with the long tubes.In case it's not obvious, when you stack structural members and put a load on them, you essentially get the stiffness and strength of all of them totalled.  But weld them together so they act as a single, deeper beam, and the stiffness and strength go up exponentially.  Without welding them together, deflection would have been about .043" (only slightly more than with the 1/2" plate), but welded together, it drops to less than half that. If anyone wants to check, I get a composite moment of inertia of 3.00 in^4.  This was a back-of-an-envelope calculation, literally, so it would be nice if someone checked the work.As to the suitability of the design for the intended use, and whether or not it's safe with a given load on it, I'd rather not get into it.  Too far into internet engineering for me.
Reply:Originally Posted by JohnRWell, I finally got around to building a cart/welding table based on a 2x4" piece of 1/2" plate. I was inspired by a picture I saw here, but I cannot remember who posted it.