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Welding table question

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  • Welding table question

    This isn't a machining related question, but it is metal related, and I'd appreciate any input you can give.

    I'd like to get a 4' x 8' sheet of 3/8 thick steel plate sheared into 3 pieces, each 48" x 32" to place on top of a fence jig that I use for building steel fence panels.

    The purpose would be to have a flat surface upon which to weld together some other projects. Iron furniture * wine racks, tables, etc..)

    I'd rather not build a dedicated welding tabel of this size just yet, hence my reason for putting the top on an existing jig that I have.

    I'd place each of these sheets so that they overhang the side rails 6" on each side of the 2" square tube. Without additional structure, there will be 32" of unsupported sheet.

    How much "bow" / deflection can I expect to see?


    pics of the jig below.

  • #2
    Depends on how much weight you intend to stack on them,but I have a similar top on a small roll around table at work and it deflects about 1/16" with 400lbs in the middle.

    If you wanted to stiffen it up,just tack a couple truss straps across the bottom.They can be anything light,3/4x1/8 flat 3/8" round bar etc.

    Steel sheet being what it is,finding something flat will be tough,something that stays flat after it's cut tougher.You might need the truss straps and a bottle jack to get them flat after cutting.

    I have also taken a plate,framed the edge with 2x1/4" flat bar and then ribbed in between with more 2x1/4 falt simulating a ribbed castiron machinetool table.

    Oh,BTW,nice looking jig!
    I just need one more tool,just one!


    • #3
      If your not doing any pounding or hammering on them - and you dont leave them on it for an extended period of time - and you store them laying flat - i don't think you'll have a problem.

      I know 3/8" by 8" over a 24" span doesnt deflect nearly at all if that helps any...

      1/4" by 24" by 12" will sag naturally with time - my brother-in-law has got some covering up drains in thier new shop and after about a year you can pick them up and see they are pretty badly bowed. They were covering 8" diameter holes.

      Otherwise just add some ribbing underneath to stiffen it up. Try it and find out whether it will be stiff enough for you - if it isn't get a bit of scrap strap and weld it underneath. This will help alot, especially if you make it so the ends of the strap are resting against the tubing.

      edit - just listen to weird science...
      wow i didn't consider myself a slow typer but he certainly beat me to the draw...


      • #4
        Whoa, that was a quick set of responses, thanks.

        The working surface will rarely see loads above 50-75 pounds and that load will be spread over a pretty large area of the surface.

        I can't weld it to the structure and have it removable, so I was planning on welding some "L" brackets to the underside of the plate that would have holes through which I would bolt into threaded holes in the tubing.

        Thanks for the compliment on the fence jig wierdscience, it works really well for my needs ( lots of different sizes of short runs, though I have put a couple of 2000' jobs through it)

        Last edited by 67chevelle; 01-30-2007, 11:42 PM.


        • #5
          If you want your pcs flat when you get them, ask your steel supplier to check the sheet for flatness before they cut it. This material can be out of flat by about 1" over 8 ft and still be within specs. You might also want to have it plasma cut, laser cut or waterjet cut as shearing it causes a pinching action which starts at one side then moves to the other like a scissors cutting though paper. It will cause twist in the pieces probaly 1/8" to 1/4" across the corners and will be difficult to get out without securing it to a solid frame.


          • #6
            What weird said and especially what fishfrnzy said about shearing. That'll bend up your plate sure as hell. I'd rather flame cut it than shear it. Plasma is better or waterjet or...
            We do this all the time...working with bowed sheets and making them flat.
            We control the bow first by clamping heavy angle to it then fine tune the bend with the pieces we weld to the plate.
            You can move metal around a lot by using weld beads of different length or fillet/bead size. In fact beginners bugger up a lot of work with the weld alone.
            Start off by placing a straight piece of angle across both ends. Back off aways and eyeball the tops of the can see if they are running parallel which means your plate is flat (or bent) on that plane. Tack it down and use dogs or wedges to adjust it flat. want a slight "opposite" bend to it if you where going to weld flat bar or angle to it. The welds will pull it into the flat you are after.
            Move the angle pieces to the other ends and repeat...eyeball them to check the parallel...adjust and tack flatbar/angle.
            You can get your plates near perfect doing this. You don't need heavy flat bar underneath. 1/8" thick X 1 1/2" wide...with the right amount of weld to pull it will be very strong.
            Hope this makes sense(might be one of those "had to be there" deals).
            I have tools I don't even know I own...


            • #7
              Hey torker thats pretty cool - i've done that with 1/8" plate? before but i hadn't thought about the using a weld to pull something that thick flat. I should have guessed it would work since the first welding table i made was out of some of that 1/4" by 24" by 12" plates and when i started welding them together, i had a nice arch out of four pieces of plate. I should have welded them to the table first and then welded them together - i dont know what i was thinking. Luckily that one was easily fixed by use of some nice 12" bessy clamps that pulled everything nice and tight and then welded it in place. If it wasn't just a table i would have been worried about the integrity of those welds - but just to hold the whole thing flat no biggie.

              Mark - if your bolting it down i definitely think you'd have no problem with it. I was thinking you were just going to lay it down on top ... which i was slightly concerned with.


              • #8
                Don't ever underestimate the pulling power of welds. I've seen a 6 1/2 foot diameter XXX heavy wall pipe rip apart a full x-rayed weld at the end of a long run of pipe. This was pennstock for a hydro dam project we installed.
                They wanted us to anchor both ends first in a 150 foot run. We argued with the brand spanking new/fresh out of school engineer but he knew better.
                OK...each joint took 20 to 30 passes with 7018, not allowed to exceed the interpass temp of 250F. When the last joint was almost done...there was a hell of a bang! The first length we welded in came apart....the noob engineer got himself a new one ripped out...the big bosses where not pleased when they found out that we didn't want to do this.
                I've also seen big beams...bent like bananas...with weld beads.
                I have tools I don't even know I own...


                • #9
                  my 3/8" thick welding table is bowed about three inches in the middle.

                  I welded a piece of 2x3x1/4 angle across the back bringing it back up. I was welding some heavy metal and it heat warped to it's present dying fish arc.

                  The ones at TVA were 1 inch thick, never did that.

                  I am sure given enough time I can figure a way to flatten it back out, triangulation with adjusting jack bolts maybe? but. I'll probably cut this one up into Parts and look for a thicker piece to make a real table from.

                  Homer SImpson alert... metal this thick and thicker likes to shear toes and fingers off. I had to move my pieces with a cherry picker on a truck bumper.. (outdoor crane)
                  Excuse me, I farted.


                  • #10
                    David, I straighten stuff like that all the time...snow plows, plates etc.
                    Put the bow up...cut two eyes out of 1/4" plate. Weld the eyes on the outboard of the bow. Run a heavy chain through the eyes. Slip a 20 ton hydraulic jack under the chain(over the center of the bow) and jack it up til the chain is tight then keep going till the plate is straight. **** I have a gadget I use to hold the chain on the jack. A short piece of pipe that slips over the ram...has a "U" piece welded on it to hold the chain.
           want to stand beside the chain...not in front or in line...duh!
                    On something really heavy I'll put a couple of old jackets over the chain to keep the shrapnel wounds to a minimum.
                    I have tools I don't even know I own...


                    • #11
                      How 'bout adjustable bow-string trusses? All-thread rod for adjusting tension.
                      Just got my head together
                      now my body's falling apart


                      • #12

                        Ok.. in the years before.. I had this girlfriend with a 65 vette.. I had to swap the rear axle out.. a tranverse spring and hydraulic jack and I tried to loop a chain under it to "pull the spring" into compliance.. Under the car, nowhere to go.. That chain almost knocked my block off.

                        I done got half a dozen things welded to this table, I started out welding 4 legs, then flipped it back over and welded casters on the legs, then a shelf underneath for rod storage, then tig welding rod shelf 4' long, then holes for sockets for dropping all the tools on 2x2's into.. then reinforcing sockets to stop them from wiggling, then I warped it all to heck. Next? I got another 3/8 sheet, It was used as a ramp getting cars out of a building and warped the "other way"... Invert and weld the two together? that would make a bigger mess I am sure. My catastrophies seem to grow. I have about twelve hundred pounds of unfinished projects laying on this 4x8 sheet at the moment.

                        THE one inch piece I welded 4 legs onto, about a foot by three.. I can bang it, set the sandbag on it, hit it with a sledgehammer and move it around. I got hammer racks welded around the legs and it jingle-jangles when I move it. Things have a way of getting complicated in a small shop. Tables have a way of getting "round" with projects here.

                        My knowledge now is, 3/8 is nowhere near thick enough for a serious welding table. If you weld things down, weld them up on the flat surface? you want to start with a flat surface. I am sure there is a bridge builder somewhere that can add five or six hundred pounds of trusswork to make it square and stay square, but starting with a one inch thick piece of metal would just make more sense..

                        I been whipped, not conquered. A jack screw in the middle ??
                        Excuse me, I farted.


                        • #13
                          David...LOL! Yup it sounds like you got a mess there alright. The jack and chain can be dangerous alright. I just used the jack, chain and I beam trick to straighten out a bent frame on newer Ford 3/4 ton. Had to use a 50 ton jack....blew the seales out of the 20 ton. Now that one was a bit scary. The guy put a snowplow on it and hit a sidewalk really hard. Bent the frame down 5" on one side. Had to bend it up 7" to get it to stay.
                          I have tools I don't even know I own...


                          • #14

                            New chevy trucks, the story told to me by a man involved in it?

                            As they'd load them onto the car haulers to leave the factory, the guys driving them onto the hauler would hit it 30 or so miles a hour, one front wheel would hit the ramp before the other.. Frames were bent at the dealership. POS new truck evidently riding on another "engineered sheetmetal frame"...

                            I have a chevy motor, been in seven vehicles now, done wheelstands in two, 160mph in a old heavy El Camino.. I got it blueprinted, stuck together on the stand. It is slated for the second motor for the 41. (after radiator check and other problems run out a few hundred miles)

                            OK.. Never again will I own a new chevy. I got a pile of chevy parts is why I am building a old one. MY 94 ranger lowrider, working on it? Mostly Mazda. My 99 ranger I bought new? More Mazda.. Funny someone said, Nascar, the only fully american vehicle racing is a toyota. Never again will I buy a new Ford, or Dodge.

                            Back to welding tables? anyone know where I can get a 4x8x1" sheet of free steel? If not I'll have to deal with the warped one a while longer.
                            Excuse me, I farted.


                            • #15
                              in my "cabinet....and misc stuff" shop.........i have several wood framed benches on casters.......i put a few together....cover um with particle board "temporarily" add some extra 2x4 leg's etc....if needed. i can do the layout on the board, drywall screw blocks of 1x or 2x on to make a jig, fit, tack the steel....finish weld as much as i can before i set the wood on fire. then flip it.

                              on one projet building some stair rails........i framed up a 8 high x 12 long wall of 2x4 24" oc...........screwed 1/2" wafer bd to it, then tipped it back about 12" from an easel. did my run/rise layout on it, screwed blocks on.etc........tacked it up......finish welded what i could reach...flipped & welded the other side.