[Madazz]

Hi all, first post!

I'm building a welding table and would like some advice before welding it up.

After getting the 1200x900x12 laser cut top home from the cutter I notice its not flat.
There is a few mm crown in the middle looking across the 900.
I have 4x 53x12mm ribs that will run along underneath the top, 1 each on the ends and 2 evenly spaced through the middle, and 3 ribs that will run across the 1200 in the middle of these.
After preliminary clamping of the 900x53x12 ribs, it seems to get most of the crown out... but this is with the crown facing down, easy to clamp the edges and the outside edges of the top pull down to meet the ribs.

The problem I have with this is that I think if anything after welding it may still want to return to a concave shape...

Should I flip the top so the crown is facing up and pull the centre down to meet the ribs, this way after welding the ribs on will it try to pull down slightly?

Should I weld the frame together first (see exploded pic) then lay the top on, clamp it down the weld it?

Should I try to flatten the steel first before welding the ribs on?

Other ideas welcomed.

Hope this all makes sense, want to do this once and do it right!

Here are some renders of what the finished product will look like.
The long sides of the top will be butted to the 65x65x6 SHS and the ends across the 900 side of the top will extend out by the way 50x50x5 sliding inside the 65x65.

Cheers

[BugHunter]

I would be inclined to weld some beads on the underside of it in order to make it pull that direction, obviously while upside down. When you get to where you feel it is flat enough, grind all the areas that you need flat in order for it to sit on your base and weld the sucker fast. It only needs tacked on the bottom side to the framework.

I would be very surprised if you could pull that much steel and get it to pull straight. You can put beads of various sizes in different places in order to make it flatten out. Just don't go overboard and let it cool to be sure where it's going to stay when you're done.

[Oscar]

Should I flip the top so the crown is facing up and pull the centre down to meet the ribs, this way after welding the ribs on will it try to pull down slightly?

That would indeed help pull it down, but it will ultimately be trial and error as to how many/how long of a weld to place.

want to do this once and do it right!

Then take it back to the place that did the work and remind them you told them you needed it flat. You did tell them that, right?

[TraditionalToolworks]

I would pull it flat, and here's how I would do it.

Go buy some u-bolts. I would get 14 of them. I would get them big enough to spread at least 2 holes so you could straddle the frame.

I would place the cup side up, so that it pulls the cup down in the center.

I would try to weld it in 3 sections.

I would start with the center, putting 2 u-bolts on each frame section, inside and outer frame sections, all the way around the grid. That will use 14 u-bolts. Start clamping as close to the center of the table as possible on that center grid so that the cup is pulled down to the frame evenly from the very center. You could place 2x4s or better 4x4s down, place the cup down and put the frame on top, this way it will be inverted to weld and pull the cup to the frame.

To be honest, 14 might be overkill, but you probably paid a hefty price for the laser cut steel, and u-bolts are cheap, like $1-$2 in the US. (not sure about NZ)

This is all dependent on your frame being flat, so make sure you have a flat frame.

Pull the cup down (or up to the frame if inverted), weld 1"-2" sections and move around to spread the heat, so that you don't distort the frame, starting in the center and moving out.

After I did the center, I would do each end, pulling it down flat (or up if the table is inverted) the same way with u-bolts. If your frame is flat you should get a flat table.

[cj737]

Crown up, clamp center to rib on the underside, weld 1” long stitch to either side. You don’t need much weld length. If the balance of the surface is flat, small stitches spread through the field of the table on underside will keep it flat. Work from the center to edge.

Sorry, just saw Toolie’s reply is very similar.

[TraditionalToolworks]

Crown up, clamp center to rib on the underside, weld 1” long stitch to either side. You don’t need much weld length. If the balance of the surface is flat, small stitches spread through the field of the table on underside will keep it flat. Work from the center to edge.

Sorry, just saw Toolie’s reply is very similar.

I would still heed YOUR advice!

Actually your post made me realize clamps on the outside of the frame would be fine, I would still use u-bolts on the inner section of the table frame. In theory if the cup is in the center and pulled down, the sides will be flat after the center is welded, but clamps would ensure it is flat to the frame on the sides as well.

Now, whether the frame is flat to begin with and/or if the frame stays flat after welding the center/cup depends on a lot of factors.

[Coldman]

Another way is finish the frame so it's flat and firm. Plate crown down, clamp edges flat and tack edges. Weld nuts on ribs screw in some bolts to push any concavity to flat, tack.

Or if the plate is already predrilled you can go concave up and bolt down to flat.

[JayWal]

Got a double post here, 2 threads same project.

Yes id say you should be able to pull it flat. But start in the middle and work out, if you tack/weld the ends and then try to pull the center down you might get the jar lid/metal can effect where it wants to pop between concave and convex, not straight. Put a straightedge across the frame, if its not flat then add shims between frame/top and clamp the top down with ubolts or clamps. Check to see if its flat, add shims if it isn't or start tacking if you're happy with it

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