View Full Version : Sheet metal warpage

Bad Bob
02-18-2005, 06:10 PM
When i was building a small tank out of .030 304 stainless, my frustration level was reaching a 10 as I watched the sheet buckle in and out. I tacked the seams every inch or two, ran beads about two inches at a time and let it cool. When I tried to tack the flange around the bungs, the sheet would try to jump away as soon as I hit the pedal. The final results were somewhat unprofessional. Any ideas?

02-18-2005, 06:28 PM

Try this stuff.
all the best.mark

02-18-2005, 07:16 PM
Good fit up and quick close tacks, no filler while tacking just enough weld time for the edges to puddle then on to the next tack half an inch away. Doing bungs you could use large washer & bolt clamp type arangement to help while tacking.
How good a quality do your tanks need to be. I used to fabricate large stainless tanks for a living so I have seen some of the secrets in making good stainless tanks.


Bad Bob
02-18-2005, 07:19 PM
Looks like the heat stop paste that Brownells sells for welding bolt handles and such. There was a tub sitting in the cabinet over my head when I was welding at the bench!

02-18-2005, 08:50 PM
John said it well. Use the smallest tungsten to match material thickness (.040 SS & .040 tungsten). Try the lowest heat that will quickly melt & make small tacks.
Let the material cool so you can put your hand on it before you weld again in the same area (about 250F interpass temp). This will MINIMIZE, but not eliminate warping.

02-18-2005, 09:13 PM
Bob...2" long beads seem a bit much to me if you want to keep the heat out of it. Any light guage stuff I do see 1/2" to 3/4" long beads at most. I used to gas weld .050 alu tanks and had good luck keeping 1" thick by 2" wide steel blocks beside the HAZ to act as heat sinks. That's pretty thin stuff you are welding there..that might make a difference.

02-18-2005, 10:43 PM
You say small tank, what is small. With that thin of material. As far as the tacks I just do a spot sized tack, one about every inch or so. Technically you should have a .030" gap for full penetration but for what you are doing you could just butt it up tight. The tighter the better. Then I just run one continuous bead, no filler, rather quickly. I like to weld TIG faster and hotter instead of cooler and slower for thin sheet butt seam welds. JRouche

Now, I'm not a welder by trade so you better listen to the others http://bbs.homeshopmachinist.net//biggrin.gif JRouche

02-18-2005, 11:29 PM
Some good suggestions there JR. A gap is not a good way to get full penitration on stainless though, better to purge the vessel with argon or use pasivating tape. With these methods you get a good sealing bead on the oposite side rather than the horrible black jagges you will get even with a gap. I could have said a lot more but not knowing the size and purpose of the tanks that Bob is making. There are all sorts of considerations like thermal & pressure cycling, especially important with the work hardening charactoristics of stainless. But all this is unimportant if it's say just to hold some water for cooling the tig torch or similar, then a quick controled continues beed with no filler and as little heat imput as possible will do the job and look great.


[This message has been edited by zl1byz (edited 02-18-2005).]

02-18-2005, 11:41 PM

[This message has been edited by zl1byz (edited 02-18-2005).]

02-19-2005, 12:28 AM
I have done a lot of stainless and cs tanks of various sizes.

Assumming your making a square or rectangular tank,the way I do it is to clamp up and weld four sides into a hollow tube first,then add the end caps.Bungs should be put in the sheets and flattened after cooling before any seamwelding takes place.

As for purging,I use a length of angle iron with the corner ground off to leave a chamfer about 1/8" to 3/16" wide,Clamp the sheets to each side of the angle with the seam to be welded over the chamfer.Close the seam up tight,then make up a purge line from 1/8" tubing,stick it in one end of the chamfer.

With all that ready,forget the tacks!With the sheets clamped at each end you won't need them.Fire up your rig,start the purge and then fuse the seam for the full length in one pass without stopping.

Once you have a four sided tube then do the end caps.Tack one corner,then the opposite pulling with clamps if need be,then tack the other two corners.If the seams aren't tight,tap the tacks with a hammer until they close then single pass seal weld them working in either a cw or ccw order(which ever is easy for you)

On stainless that thin,you can simply fuse the seams so long as you purge the back side while welding.There really is no need for filler.

02-20-2005, 01:58 PM
Cut two pieces, bend into "U" shape then weld them together - this leaves only 4 seams and 4 corners to weld and a stronger tank. I would actually flange the body, but that requires a notcher to do the corners, bit it elminates any buckling - also allows you to weld in one bead down ech edge after tacking - if you ae "good" you can weld each end without stopping and it will be "Beauty"

[This message has been edited by Thrud (edited 02-20-2005).]

02-20-2005, 02:22 PM
If you are "fusing" the seam you can get away with longer beads. Most problems occur (in my experience) when you have to add filler. With material that thin nearly any hand fed filler will end up thicker than the base metal and cause warpage problems!

Bad Bob
02-25-2005, 06:05 PM
Thanks for the replies. It's great to see the wealth of information always available from our group. The tank is to replace the five gal. water storage tank in my camper (the plastic one finally cracked after 38 years).