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Tony
08-02-2011, 03:24 PM
Before I go ahead and do something stupid / the hard way, thought I'd
bounce this off the group..

I've got a big heavy welding table I'm fond of.. 3' x 6' with a 5/8" top.
its seen better days. top is no longer flat. Theres a dip in one half almost
1/4".. I've made a little drawing.

It stills seems flat in the short (3') direction. But in the long direction, 1/2
the table has had the live'n bejeezuz beaten out of it.

Thought about cutting the top of .. but (1) thats alot of steel to throw away
and (2) i was a little over zealous when I welded it up 10 years ago.. and it'd
be hard to do.

I'm thinking of laying out a grid.. maybe 6" x 6" and building up "spot welds".
Then using a straight edge, grind the weld bumps down to level.. and drop
a sheet of 1/4" or so sheet on top.

Here's the concept. Red dots are weld:

http://img.photobucket.com/albums/0903/knucklehead/weldtablewarp.jpg

easier way to do this? I don't think I'll be bang'n as hard.. maybe 1/4"
is overkill? I'm afraid 1/8" or so would warp when I weld in place.

-Tony

aboard_epsilon
08-02-2011, 03:29 PM
just prop something under one or two legs of the table ..it may correct it

all the best.markj

Black_Moons
08-02-2011, 04:01 PM
Hmmm. Id kinda wonder about taking it to a professional metal beater (Like torker)

Some torchs, Some beating with a big hammer. Some slaping with wet rags(?), Some attacks with hydraulics.. Maybe even welding some beads on it to bend it with stresses.

I don't think you'll want to hammer on 1/4" sheet with spotwelds supporting it every few inchs. Seems like it would vibrate like crazy, And quickly get dents.

Id think 3/8" if your gonna put a new top on it, then you can beat the hell outta it without it bending/vibrating/rebounding.

Shuswap Pat
08-02-2011, 04:14 PM
Your spot welds will shrink it more, making it worse. Use a rosebud, and heat some spots on the 'Long Side' (back) this will upset the material and cause it to shrink when it cools. Heat a couple of spots, and then leave it alone to cool - you can speed it up by using a garden hose. Repeat as required - don't rush. We straighten beams and plates prior/post fabrication this way. We have even done 20' long 10" diameter pipe rolls - run within a 1/16" TIR.

Pat

metalmagpie
08-02-2011, 05:16 PM
Remove the 1/4" plate safely. Move your table or stuff around it so you can splatter some water and it won't hurt anything nearby. Run a water hose with a squeeze-type nozzle on it, a good one that can withstand full pressure and not leak when you aren't squeezing it.

Get a long trustworthy straight edge and a piece of soapstone. Draw on your 1/2" plate where it's low, so you know the entire topology just by looking at your soapstone markings.

Get your hands on a big propane rosebud setup. You're going to use most of a 250 cubic foot cylinder of oxygen. With your water hose close at hand, fire up that big torch and, starting at the point of greatest warp, heat a spot on the bottom of the table so it glows cherry red about the size of a silver dollar. Move the propane torch and immediately direct a strong stream of water onto the spot. It will steam like crazy for a second, then cool. The material in that area just shrank a bit. Move about 4" in the direction of greatest warp, and repeat. Work in a pattern that gradually fills up your entire warped area. You will be shrinking the plate so it stretches tighter and tighter like a drum head. In doing so you can get a lot of the warp out. If you're lucky, all of it.

But for now let's assume there is still some warp left. Clean up the water mess and dry up your table so it doesn't rust. Now do the straightedge/soapstone thing again so you can fix the new topology in your mind. The next thing to do is get some stiff steel stock like 5/8x3" flat bar (that's pretty dang stiff and also *heavy*, you might have to settle for e.g. 3/8x1-1/2") and use either clamps or saddles and wedges to fit the bars under the sag and pull them up on the ends to lift the sag out of the plate, then weld them strongly at the ends and in maybe one or two places in between, no need for 100% weld here! You should be able to get it really close this way, depending on how much work you're willing to do.

At that point you might declare victory, or you could go even farther and put down a coat of Bondo over the entire surface and then use your straightedge and a lot of time with sandpaper to get it as flat as you like. I'm assuming this is truly a welding table and not something you head red hot, 'cuz if you do heat it a bunch, the bondo would emit bad fumes so don't do bondo.

Theoretically you could level your table very carefully and superheat melted lead and pour it into the depression and it would flow out and fill it, but sadly I doubt this would work well.

Anyway, good luck. I've been contemplating building a new welding table, and if I do, it will have bars on edge underneath in a framework, welded to a piece of plate, the whole thing being something like 2x4', then take the whole weldment to a grind shop and have them grind it flat on a Blanchard grinder. It should stay flat because of all the structure below. Then add legs, casters etc.

metalmagpie

metalmagpie
08-02-2011, 05:22 PM
I like to refer people to the oxyfuel shrinker's Bible: "Flame Straightening Technology for Welders" by John P. Stewart. Sadly, a very expensive book, but my library can get it for me via interlibrary loan. I do have a brief excerpt from it which you can access here:
http://www.tinyisland.com/images/temp/flameStraightening.pdf

Tony
08-02-2011, 05:38 PM
Thanks all. Flame straightening sounds intimidating. But that aside, the
table has quite a few angle iron stretches welded across the bottom. I'm
pretty sure they're all bent up too.

I think my best bet (personally) would be to add a clean plate to the top.

I just got to figure out a smart way to do it. I'm glad I asked though.. like
I said, I was going to spot weld the whole top surface.

aboard_epsilon
08-02-2011, 05:48 PM
Thanks all. Flame straightening sounds intimidating. But that aside, the
table has quite a few angle iron stretches welded across the bottom. I'm
pretty sure they're all bent up too.

I think my best bet (personally) would be to add a clean plate to the top.

I just got to figure out a smart way to do it. I'm glad I asked though.. like
I said, I was going to spot weld the whole top surface.

just bolt it on with shims underneath in the depressions ..lots of them

all the best.markj

Boucher
08-02-2011, 06:19 PM
Tony, Try taking some 3" X 1/2" flat and clamping it to your table edge wise and see if you can pull it straight. If you can weld it. This is what my table looks like.
http://i109.photobucket.com/albums/n50/boucherbyron/IMG_0038.jpg
When I was building it, the amount the 1/2" top would flex surprised me. The flat bar welded to the top cured that problem.

Paul Alciatore
08-02-2011, 06:42 PM
Thanks all. Flame straightening sounds intimidating. But that aside, the
table has quite a few angle iron stretches welded across the bottom. I'm
pretty sure they're all bent up too.

I think my best bet (personally) would be to add a clean plate to the top.

I just got to figure out a smart way to do it. I'm glad I asked though.. like
I said, I was going to spot weld the whole top surface.


Just spit balling here, but would it be a good idea to add a filler between the 1/2" and 1/4" sheets? Weld it up your way and leave a few holes in the top. Pour in a concrete filler and then weld up those holes when it is hard. It will crack with use, but still fill the voids to help stiffen the 1/4" top.

Black_Moons
08-02-2011, 06:51 PM
Just spit balling here, but would it be a good idea to add a filler between the 1/2" and 1/4" sheets? Weld it up your way and leave a few holes in the top. Pour in a concrete filler and then weld up those holes when it is hard. It will crack with use, but still fill the voids to help stiffen the 1/4" top.

Brass! braze the new top on. heheh.

mf205i
08-02-2011, 07:31 PM
A friendly reminder to those that havenít thought this through, NO AEROSOL CANS ON A WELDING TABLE, EVER. Think about it, an accidental arc strike, unintentional grounding, or a mechanical puncture and all in the presence of a reliable source of ignition. I can assure you that he wished that he had not survived.
Take care, Mike

Paul Alciatore
08-02-2011, 07:32 PM
Brass! braze the new top on. heheh.

Are you suggesting he fill the void with brazing alloy? Wouldn't he have to heat the whole tabletop to brazing temp at one time?

KEJR
08-02-2011, 10:16 PM
I agree with the guy who said to put some shims under a new table top. If you are out in an extreme sense you might build it up or true it up a bit.

You can control a shim alot better than weld beads or lead or bondo. Unless you need to support huge weights on this table I wouldn't worry about supporting it more than every few inches with shims.

If you really need it to be super flat we are talking about something else completely. I am assuming you aren't going to be welding to extreme flatness tolerances.

fciron
08-02-2011, 11:06 PM
I hate to be the naysayer, but if the 5/8" original top got bent, what chance does a little piece of 1/4" have of staying straight?

Best suggestion I've seen is the really big ribs and clamps (This is not a good job for angle iron. It's not stiff the right way and half the mass is bending the 'easy' way.)

I've got a piece of one inch plate for a welding table and it's about 1/4" low at the corner where the vise used to be. If I need something good and flat I put it on shims and level between them. This also lets splatter and other little bits of debris go somewhere. I don't think I'd trust anything without substantial ribs on the bottom to stay flat, and even then I'd still check my work.

Tony
08-03-2011, 09:03 AM
Did an experiment this morning.

Here's the offending welding table:

http://img.photobucket.com/albums/0903/knucklehead/table1.jpg

Don't know if you can see this in the picture.. but there's a gap
along the bottom of the 2nd half of the aluminum straightedge.
Its 0.2"

http://img.photobucket.com/albums/0903/knucklehead/table2-1.jpg

Threw a piece of Ibeam and a bottle jack under the table and look what
happened:

http://img.photobucket.com/albums/0903/knucklehead/table3.jpg

Took almost all the warp out in the vicinity of the jack. I may be able to
pull this off with a couple of jacks and some reinforcing ribs welded to the
bottom!

Might turn out a bit "lumpy" .. but better than what I got.

Sorry pictures are blurry.

Thanks all for suggestions so far.