Bending Metal

[bigcreek]

I have an item I cut on the cnc table from 3/8" thick mild steel which is about 2' wide and 10' long. When I pulled it off the table I didn't notice a bow but it must have been there. In any case it has a bow of about a 3/8" raise in center. I laid it on the welding table and clamped the piece in the middle then chained to one end and lifted with the forklift. I did that a number of times trying to get it to straighten out but it was having none of it and kept springing right back to where it was. I bent that thing probably 10" to the point I was afraid to go any further for fear of it buckling and then having a permanent crease in that spot that Id never be able to get out. I would have put a rosebud to it but Im in the middle of moving to a new shop an hour away and most of my stuff is already moved to the other shop so heat wasn't an option since it was already moved. Are there any other things you guys would do to bend this straight?

 

[joe49]

If surface finish doesn't matter peening the concave side will straighten it. If you want fast make a pair of blocks 4" apart welded to some thing solid. Place your piece over the blocks concave side down and hit your piece between the blocks with a 8# sledge. This method can also be done on a press with less marking of the metal. Make marks at regular intervals (the more marks you make the straighter you will be able to get it) and work each mark for anyone of these methods. Marking a template on the floor or a table of the bend and snapping a line across that will let you gauge your progress.

 

[ovrrdrive]

Do you still have your welder?

Maybe run a few hot beads on the backside and then grind them off... Other than that you already know the torch is the best option.

 

[readhead]

Was there anything holding the table down?

 

[Fordman7795]

If surface finish doesn't matter peening the concave side will straighten it.

This is likely the best option. Its gonna take a big sledge to do it though. I wouldnt leave it on the table when doing it. Stand it up on its side and whack away. Start in the high point of the curve then work up and down and then start to spread out to either side.

 

[jimgood]

Well, this isn't much thicker than some draft horse shoes I've flattened on an anvil. It can be done cold with a 2 lb sledge no problem. You just need the sledge and an anvil.

Now, I put the concave part facing down on the anvil and hammer on the convex side.

 

[why worry]

If you happen to have a short piece of channel 4" or 6" then proceed like joe49 suggested and it will come right out. I would probably use a 5lb hammer though instead of an as it is easier to swing. If worried about finish run a couple of strips of duct tape along the toes of the channel and it will help with marring.
Dave

 

[bigcreek]

Thanks for that Joe49 Ill give that a shot.

 

[bigcreek]

Yes I did keep one welder there and that's a way to apply heat I didn't think of. Crank it up high.

 

[bigcreek]

there was not anything holding the table down but it does weigh 1800 pounds. Although I was lifting half the table up with the forklift when trying to bend it back. Man I sure appreciate all the suggestions. So would it help to bend it back if I were to lay it flat on the table concave side down, clamp it in the middle or somewhat close to middle, chain one end and lift it just a bit with the forklift so there is tension on it, then whack it good with the hammer? Or would the tension not do anything? Well Ill grab a sledge and get to beating.

 

[joe49]

When you clamp it down it will bend near the clamped spot and not evenly along it's length. You could clamp bend move clamp towards the end and bend again and repeat and repeat. Easier to control using the methods I posted.

 

[bigcreek]

Great thank you joe49