How can I stop this distorting?

[waddycall]

im about ready to weld up this stainless bracket. The tube is 32mm with a 1.2mm wall. I've no idea what grade of stainless it is - it's left over from an old attempt at an exhaust job from years ago. The plates are 6mm 316. My concern is welding the two branches on without it ending up like three bananas stuck together. This is all the material I have. Current plan is to clamp it to a length of 40mm box. Any other suggestions?

 

[Paul.]

Distortion is inevitable on that type of structure, a good joint fit up, minimal filler rod and keeping the heat down by turning up the amps a tad and moving quicker is how I would do it, however 32mm tube will straighten easy enough, weld the joint nearest to the end first then when its cool clamp it down to the bench(being careful not to crush it) and give it a tug to square it up, then fit up and weld the second joint and use the same method to straighten it, to avoid distortion in the long tube a better solution would be to use pre formed tee's then make butt joints,
http://www.mig-welding.co.uk/forum/threads/how-to-make-a-handrail.22424/#post-249100

or
http://www.mig-welding.co.uk/forum/threads/a-few-random-stainless-jobs.54058/page-5#post-851504

 

[Richard.]

Stainless is prone to distorting more so than steel due to its low conductivity. I do quite a bit nowadays small brackets and fabs etc and the way around it is clamp it well, weld it to within the heat limits of its thickness allowing you to move as quickly as you can. I have a couple of big thick corner clamps that I made years ago which are great for clamping to while setting, tacking and welding. I made them in a way that keeps a whole right angled joint open so that it can be fully welded before release. The trick with stainless is sequence and lots of clamping.
I have 8-10 G clamps of various sizes and have had them all on one or 2 jobs in the past holding it in place and I'm not equipped to take on big stuff I'm talking small frame work stuff.

 

[waddycall]

Thanks chaps - lots of clamps it is. Really like the dairy fitting idea gives a really clean finish too. This job needs to cost nothing otherwise it's not worth doing so I'll weld it up as is.
Cheers, Pete.

 

[Paul.]

You could clamp it to a piece of heavyish flat or a flat bench with a thin packer opposite the weld to pre set it, its a bit of a black art knowing how much to set it though, a piece of 1.2 or 1.5mm sheet would be my choice, the variables of welding speed, weld size, effecting the heat are trick to predict until you have done a few.

 

[Paul.]

Tip of the day time, to prevent g clamp damage to your tubes make some clamping plates like these, longer ones with a slot in them to allow joint access can also be used for setting up straight butt joints,
sketched on an envelope as per the best engineering traditions.

 

[waddycall]

Excellent - get a use for some angle off cuts too!

 

[Shox Dr]

It's going to bend more along its back, too much and it will end up like a 50p.

I'd clamp as suggested but also put some preload along the back, very good fitup, tack in four places and weld a -/+quarter and COOL. Move and repeat. Making sure the part is cool to the touch.

 

[waddycall]

Well I clamped it to some 40mm box and took my time. I didn't pre bend the main tube as I would have struggled to get the branch square. Anyway it came out alright and we now have a much better t.v. picture! Cheers, Pete.

 

[Richard.]

Very nice little job.