Thread: Flattening a steel plate

Hi Everyone,

I was lucky enough to score a 900x600 plate of 10mm steel gratis. Great I said to myself - that's the top for my new portable welding table. Obviously I'd like it to be dead flat, but it's got a slight bow in the one of the long edges of about 3mm.(the other 3 edges are good)

I've tried a few things to flatten it out, including parking the 4wd on it with support shims in strategic places. If deflected nicely, but sprang back exactly when the weight came off. Haven't got an oxy set. I'm now considering running a few weld beads over the back of it to pull it into line.

Any other ideas (or tips on weld placement)?

thanks

- Mick

A BFH- big flammin hammer- judiciously applied at the correct spots will sort that pissy little bow out.

Using chalk and a straight edge-long ways and cross ways, plot the area out and wallop the high spot while the plate is supported on a couple of 4 x 2 s

A big sledge will do it if handled correctly.


Grahame

Originally Posted by Grahame Collins

A BFH- big flammin hammer- judiciously applied at the correct spots will sort that pissy little bow out.

Using chalk and a straight edge-long ways and cross ways, plot the area out and wallop the high spot while the plate is supported on a couple of 4 x 2 s

A big sledge will do it if handled correctly.


Grahame

I agree, bonging on it with a big hammer, and if you go too far a few judicious belts on the other side will fix it.

In contrast to the big beater method that bends the plate from the convex side in the same way you tried with your truck. You can hit the concave side with a ball peen hammer lightly a whole bunch along the length. It stretches the surface of the metal on that side which gradually flattens the plate. if you have access to a shot peening machine (type of sandblaster) you can do the same faster. Please note it will be more difficult, if at all, to achieve if the steel is hardened. Or go find a bigger truck.

Pete

Peter - Interesting ! - didn't know that could work, but probably beyond my patience levels. thanks for thinking about it though.

Grahame/Graziano - thanks. I gave it a few wacks this arvo and got it pretty good, so job done.

I have to admit I'm a bit disappointed though - I was expecting suggestions involving a lot of finesse, fine tuning, straight edges, feeler gauges, clamping, hydraulic jacks and the like. Although Grahame get's extra points for the spiffy diagram.

Do ya reckon the welds on the back would've worked? - Mick

In a word - maybe!

Lately I have been building lots of large frames (upto 1200mm length sides) out of different sized RHS(50x50, 25x25, 50x25, 35x35, etc).
When ever I do a "T" joint - butting one tube into another - the top part of the "T" always bends toward the butted piece.
If I need it neat I put the same amount of heat(length and duration of weld) on the diagonally opposite corner/side, let it cool, and then grind it off. If you are accurate in the amount of welding you do, the RHS straightens up perfectly.
Whether this would work on a solid sheet of steel I cant be sure - but I think it would. I think a thick sheet of steel would act the same - pretty much two sides of an RHS without the gap in the middle. Thinner sheets might work differently - much less heat would be required if you were trying to distort/straighten steel instead of welding it.

My 2c.

Bloke

U have one of them Kangaroo Jacks, use that. Take the bolt off the end and the plate, take the jacking bit off and turn it around. becomes a BIG MIGHTY CLAMP. I had the same problem, made a steel bench for my workshop out of RHS, got the plate cut to size to fit, get it home and it has a big dip one side, big bow the other. Scratched me head then remembered when I bought the jack, u can turn them around to become a clamp. Lucky I have two jacks.

I clamped the plate to the top bow up, then clamped the two jacks to the bench. Had my Boilermaker nephew do all the welding with the stick welder, a few whacks along the way helped too.

Is good, is flat.

DD

Anything wrong with welding it to the table frame? You could put on some big weights, then weld a few runs from underneath to hold it flat.

Jordan

Cut some L shaped cleats and weld them to the plate so they stand over the frame , then you drive a wedge between the cleat and the frame and the plate gets pulled down to the frame .Then weld the plate to the frame .Remove the cleats when finished.

Kev.

Dog and wedge?

I made the top frame out of 50 x 25 RHS and was worried that the plate would just bend the frame if I welded it up under load. Also I figured if I could get the plate flat first then I could just square the frame etc up easy by building the table upside down from the plate up. I did try all sorts of clamping and weights, but didn't have a good surface to wedge against - so resorted to the sledgie.

Here's the table made up - nice to have a little table to roll around where needed. I'll probably a little rack or drawer later for bits and pieces. Cheers - Mick

Originally Posted by WelderMick

Peter - Interesting ! - didn't know that could work, but probably beyond my patience levels. thanks for thinking about it though.

Grahame/Graziano - thanks. I gave it a few wacks this arvo and got it pretty good, so job done.

I have to admit I'm a bit disappointed though - I was expecting suggestions involving a lot of finesse, fine tuning, straight edges, feeler gauges, clamping, hydraulic jacks and the like. Although Grahame get's extra points for the spiffy diagram.

Do ya reckon the welds on the back would've worked? - Mick

yes mick it does,i regularly straighten plates and flat bars,tbars,angles and channels with welds,arc is normally more successfull than mig but too much is an easy stuff up to make,be patient.

Originally Posted by danielhobby

yes mick it does,i regularly straighten plates and flat bars,tbars,angles and channels with welds,arc is normally more successfull than mig but too much is an easy stuff up to make,be patient.

So Daniel, do you have any rules of thumb you follow to get just the right about of straightening? or do you just go for it and correct later? Cheers - Mick

Originally Posted by Grahame Collins

Dog and wedge?

Yep thats the one

Kev.

Originally Posted by WelderMick

So Daniel, do you have any rules of thumb you follow to get just the right about of straightening? or do you just go for it and correct later? Cheers - Mick

I used welds to straighten a 4.2m length of 5mm thick 100x50mm RHS that I'd welded eleven purlin brackets onto. I'd welded the brackets on one side and the bow was pretty noticeable when I'd finished, so I turned it over and used the stick welder to make a hot wide arc with a large air gap, this used very little filler rod and ran it side to side to give about a 10mm wide line opposite the bracket welds.

In other words it deposited little filler rod but did heat a 10mm wide strip but the same length as the welds on the other side to the welds. I started opposite the middle bracket then went along and did opposite every second bracket working towards both ends out from the middle. By the time I reached the ends and let it cool between welds it had been pulled very straight. Also it was hardly noticeable after painting.