Need advice for wobbly legs

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Hi all,Just registered for the forum. I started welding about 6mos ago. All MIG for now. I am a woodworker by trade but wanted to expand into metal. Recently I welded up a couple legs for a desk I'm making. I used 3x3/16" steel. I feel like I've seen designs very similar to this all over so I wasn't worried about stability etc. However, when I finished the legs and put the desk top on it there was so much "wobble" in the legs that I now have to alter them to stabilize this.Can anybody here lend any advice as to what methods work best without compromising the design too much?? I plan on reinforcing the top with more 3" flat bar to make a wider bracket base with which ti screw to the desk surface....but I'm lost as to what to do with the legs themselves....Do I need to run a piece of flat bar along the floor connecting the 2 legs to shore them up that way??? OR did I just make the initial mistake of using too light of a gauge (My welder only accommodates up to 3/16" material).Any help is greatly appreciated!! Attached Images
Reply:How do they wobble?  I would think that 3 inches wide would be wide enough to just screw the legs as is to the top and not get side to side wobble.  I would think you may bet front to back wobble from deflection, or bending, in the upright flat bar.Adding a horizontal piece in the middle might help, but an angled piece from one top corner to the opposite bottom corner would be more effective.  If the wobble isn't too bad adding gussets i the top corners may be enough.  Adding another piece of 3/16 on the upright pats so they are double thickness would be the best way to stiffen without changing the look.The stiffest thing that would leave the trapezoidal opening would be to make a full length inside piece that was cut to fit in the corners forming a T shaped cross section from top to bottom.  So it acted as a gusset in the corners and a stiffener for the uprights.If you were to start over I'd suggest 1 x 3, 16 gauge rectangular tubing.
Reply:Assuming you still have some of the 3x3/16, you could run one piece across the top of each leg piece from one leg to the opposite one to create a boxed section at the top. This way it won't alter the look of what you have much if the wobble is side to side. A gusset added to each top corner would eliminate any front to back wobble. Possibly adding one more piece across the center between each leg piece will help too, at the bottom.
Reply:I think if you tie the legs together at the top with more 3" x 3/16" you will eliminate the wobble.  I doubt you need to tie them together at the bottom.Using 1" x 3" rectangle tubing would be much stronger though.GravelThe difference between theory and practice is that in theory there is no difference.
Reply:Your design allows flex in 2 dimensions -- front to rear and twisting.  Adding gussets will not solve your problem -- you'll still have flex wherever the flat bar is unsupported.  If you lock one of the pieces in a vise by the foot, you'll see what I mean.  A simple fix would be to line the inside of it with 1" square tube, using whatever the thinnest wall thickness is that you can get.  Another option would be to weld in a piece of sheet metal that completely fills in the opening, then cut the center out of it so you have a window.  Leave something like 3" of the frame intact.  This would still allow some twist, but it'd probably be solid enough.  You could do the same thing by turning flat bar on edge, too.
Reply:Which way does is wobble?  Long side or short side?I recently made a conference table with same leg design.   It was a 4'x8' top with almost 2" thick walnut.  The top was 2 pieces with a power strip in the middle for plugging in laptops etc.Normally I would choose rectangular tubing as it is more rigid but the client wanted flat bar.  I used 5"x1/2" flat bar with 5"x1/4" flat bar on top with a piece of 1" sq tubing spanning the length and attached at the legs.  The legs were nearly 100 lbs each and very stout.  All joints were cut and welded and then the bottom joints were ground and smoothed.  The table had nearly no wobble, very solid.Here is the top plate.  I welded the bar to the sides but apparently didn't take a picture of it First pass on one of the bottom jointsOne of the bottom joints, multipass.  It was a shame to have to grind it all down and smooth it but that's what they wanted.Finished tableOthers have already suggested good solutions.   If it wobbles short side to side then add gussets or flat bar perpendicular to the top plate and tie into the legs.  If long side wobble then make the top plates wider.  Also, how heavy is the top?  That can worsen the wobble.  You may need thicker steel.  Last edited by Going nowhere; 08-12-2014 at 04:32 PM.
Reply:3x1 tubing 14ga should serve you well for that design.  It looks like they have a slight taper towards the bottom.  If you only have a 110v mig then that might be you best option.  You could use thicker flat bar and do a multipass weld with your 110v mig, it's not a critical weld.  Tubing will have much less flex than flat bar and it's lighter as well.Also, welcome to WW!Ben
Reply:Originally Posted by humantorch...what methods work best without compromising the design too much?...
Reply:3/16 is just really flimsy stuff. See how "Going Nowhere" drilled a 5" piece of 1/2 plate with, what looks like, a 4" eye to eye bolt pattern? that is what you need to keep it from rocking. That is a solid mount. A single bolt acts like a pivot. Hell, 1/2 plate with a single bolt is a pivot. You gotta have two holes like Going Nowhere.I'd take it a step further and use a thread/glue in threaded insert in the wood so you can avoid using a lag bolt to anchor to the wood. Use something like this with a 3/8 or 1/2 socket head cap screw.
Reply:I think this is the best looking rework and will result in very stiff legs.
Reply:Example of why most welders are not designers. The intersection of the metal and wood in a equally important joint, probably more important. there is a way to do it right so there is no wobble and you don't hog out the wood if you have to disassemble the legs several times over the life of the table. To the OP, looks like you bent the legs at the floor. That is a nice, clean look. I think the 3/16 might work but you have to tie the current leg assemblies into a wider steel bracket. Do you have room (thickness) in the wood top to counter sink a piece of 5" wide 3/8 thick cold roll steel in the under side of the table top? Counter sink the metal and bolt the 5" plate with the wood threaded inserts. Once the 5" mounting plates are bolted to the underside of the top, stand the 3" wide legs into position and weld them into position with several heavy tacs. probably 6 1" long welds on each side of the 3" leg. All of this being done with the desk upside down on your work table. good luck. I dont think you really need to scrap the legs, you just need to tie them into the desk top really really well.
Reply:Put a small 'S' scroll in the corners, it'll spruce it up a bit and add some rigidity. I'd use 1/4-3/8 round or if round isn't your thing 1 x 1/8 flat. If you want to go corner to corner diagonally, which would stiffen it up a lot more, make the scroll corner to corner...Mike
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