Metal "bending"

[Paul C]

Using a mig welder to weld a handrail together, having problems keeping the top and bottom rail from bending. When welding the vertical pickets, the horizontal top and bottom rails are bending. The welding is drawing the rails causing them to bend. Any suggestions on keeping this from happening and straightening the rail after it is bent?

[sn0border88]

Give it time to cool in between welds and skip around to spread the heat around. You can also try using heat sink gels to absorb more of the heat. Kimball Midwest makes a great product for that.

[lugweld]

Are you using tubing or solid bar?


The answer depends on what kind of material you are using.

[tapwelder]

Brace the top and bottom rails with another piece on metal or tack them in position on a table. Get all picket in and tacked before solid welding. Easier to builds rail on a table rather than vertical.

[Bob]

What tapwelder said.

[Craig in Denver]

Are you welding verticals at 4 inches or 10 feet? Someone here made a large clamp that 'back bent' the top and bottom rails before welding. Doing this on 4 inch centers wouldn't be practical.

[mrmikey]

Something similar to what Craig said. Prebend the rail the opposite direction that it's going to bend, experience will tell you how much. I've used that method before and it does make a difference....Mike

[lugweld]

Pre stressing is a good idea, but not always reliable on imported metals because of their poor standards of manufacture.

I make jigs that firmly hold the metal first. But watch your heat levels. Most decorative things need a good tacking and not much more.
Fit all you pickets first.
As you weld. start on the out side then weld the middle then go to what the middle bars would be between your outside bars and your middle bars then proceed to find the next "middles" until you have everything tacked firmly together.

Make your tacks on the outside seam first if you are welding flat on a table so that your pickets won't pull. Then tack the insides and finally flip it over to tack the backside. Let every thing cool and make sure its straight. Then weld it following the same pattern that you used to tack.

[tessdad]

I would really need to see pics. Before welding, as tacked, and all welded, showing the curve your trying to avoid.
I will take a picture of my bender/straightener I built, and post it here within a couple of days.
One of the most difficult to avoid "bending" seems to occur whenf field welding sections together. I try my best, and if I get something not straight, I bend it back into place. I have been looking at and wanting an excuse to buy a "Porta-Bender", it looks like a great tool, check it out, I copied the principal of it with a small Port-power piston and a standard pump.

[Paul C]

Thanks for all the info. The material is tubing and the pickets are at 4in centers. Haven't been clamping the top and bottom rails along their entire length. Sounds like I need to make sure it is clamped properly tack...let cool...weld...let cool...then unclamp.

[pistolnoon]

It may not be practical for the thickness of steel you are using but you couyld try normalizing it "immediately after welding small welds with a cross pein or welding hammer?Tack it keep your welds small, move around and try keep your heat down.

[Donald Branscom]

Originally Posted by Paul C

Using a mig welder to weld a handrail together, having problems keeping the top and bottom rail from bending. When welding the vertical pickets, the horizontal top and bottom rails are bending. The welding is drawing the rails causing them to bend. Any suggestions on keeping this from happening and straightening the rail after it is bent?

The result of all welding is shrinkage.
If the rod you are using or welding wire has an elongation rate of 2% per inch of welding that is how much it is going to shrink. Example. 6 inches of welding total, and 2% of 6 inches is = etc.,.

I you make all of the welds on one side of a tube and transverse to the tube the tube will curve WARP a lot.
What you need to do is cut all of your vertical pickets and make sure they are all the same length. Then tack weld the fence section together. Start in the middle and place one vertical on each end, and work your way from the middle towards the ends. Tack only.
Keep it clamped together. Check squareness.

After the entire piece is tacked, start to fully weld in the verticals but only weld the SIDES, NOT transverse across the bottom and top rails! That way when someone looks at the fence it looks clean. Start in the middle and work your way towards the ends but work on both sides also. No transverse welds.

The size and thickness of the tubes is important. You need to use thick material for longevity due to corrosion over the years, and to cut down on warpage.

Before 1930 metal fences were put together with solid rectangular bar with set screws completely.
I have repaired many of those because the set screws rusted away. The really thin tubular fences that are just for decoration are rivited together.

I would look at other well built fences when you get the chance and start making some notes as to what looks good and how they were welded together.

Remember that with MIG welding it is so fast that you can get into trouble with warpage easily. So tack weld the thing together FIRST.

Some welded gates are made quite heavy for security purposes so you can use heavier material and not worry quite as much about the warpage BUT it is always a factor.

Unfortunately many welding schools do not teach design of weldments. They only teach welding.

[nosleepno]

Great explanation Donald.

... PS, your from Guerneville? I am in Sebastopol.

[Donald Branscom]

WOW !! Nice to meet a neighbor on the web.
If you have any other welding questions feel free to email me.

BTW I am always telling people to put their address, State, City and phone number
on their web page because you could have someone in your neighbor hood that may have simular interests in what you do, or products you sell.

Sincerely, Don

[Matthew]

Originally Posted by tapwelder

Brace the top and bottom rails with another piece on metal or tack them in position on a table. Get all picket in and tacked before solid welding. Easier to builds rail on a table rather than vertical.

very good advice. always clamp railings down to a table. at work we use two long peices of 10" aluminum channal for that. then tack EVERYTHING in place BEFORE welding. then weld

matt