Tigging thin steel to thicker steel

[serepton]

I am pulling my hair out here!

I have a cycle bottom bracket shell which has a thickness of 3mm. I am trying to weld the rear chain stays to it and they have a thickness of .9mm.

I can't get a puddle going without blowing through the chain stays. If I wait until there is just enough heat to start the puddle then as soon as I add filler rod to the puddle it cools it too much and the puddle solidifies.

Is there a technique to doing this so it wont blow through?

Thank you

Sheridan

 

[tab]

I've found if i make the pool in the thicker material then "flick" into the thinner material as i move along that that helps me not to blow through, although i am still new to this so someone with more experience may have a better solution for you

Tom

 

[serepton]

Thanks Tom, it is driving me crazy!

 

[langy]

It's much easier with a pedal but as said heat the thick side

 

[chunkolini]

A lot of high end steel bikes have the rear end brazed on instead of welded.
my ancient Kona has a welded main triangle and brazed rear.

 

[Drains]

Serepton, as said above, get the weld going on the thick stuff and jump over, but the trick can be (apart from having VERY tight joints), getting started. You may find that a very fast blast of the amps works (this is where the footpedal comes in handy), as you can quickly jump on the pedal and dip the filler almost at the same time. Once you have the first tack in, it's much easier to keep the weld going as there is a better, more even heat transference.

Keep at it, but I would suggest you use some practice pieces first.

 

[chevy2]

Try using silicone bronze rods,
They work at lower amps and more forgiving,
Think sif 968 is the part no?
This is 20g sheet onto 4130 tube.

 

[serepton]

Thank you all for your replies,

I shall try the tips out tomorrow!

I have thought about brazing the rear end on, I would rather weld it but it could be an option.

 

[Shox Dr]

Surprised no one has asked what size tungsten you are using and tip profile, also how many amps?

 

[hotrodder]

Pretty much all been said but a few other things that can make a difference...
What diameter wire are you using? If it's thicker than 1.0mm then that'll make life harder as the thicker the wire the larger the weldpool needs to be to avoid the puddle freezing issue. As usual arc length, arc length, arc length but obviously in this case the tungsten needs to biased slightly towards the thicker section. Fit up needs to be spot on

Personally i'd practice with flat sheet initially... compared to tube the joints are quicker to set up and it also takes torch manipulation out of the equation somewhat. Once you've nailed the weldpool control switching to tube will be easier. Some people also find it helpful to go to 'extremes' hence people welding beer cans, razor blades and the like. The real job can seem quite easy after messing around like for example...

 

[citizen kane]

Tight mitres, foot pedal, needle sharp 1.6mm tungsten, gas lens with large cup, 1 mm tig wire and lots of practice. Focus on the BB, work fast, breathe and listen to the Beach Boys.

I'm kidding about the breathing bit.

 

[Shox Dr]

You wasted a good blade there!

If you'd of thought on, and turned it over at least it would have still been useful

 

[hotrodder]

Nah it was blunt. Oh hang on... Norverners... i suppose becasue it wasn't broken it could have been sharpened

 

[Shox Dr]

ey that'n stop er'n dowrs using it

 

[Rick]

Even I can't read that haha.

If you haven't got a pedal I'd get one.

Once you get the tube hot, (i.e. on a failed attempt) Leave it 5 minutes while it cools, your fighting a losing battle.
No point going over what everybody else has said again, but do all the above as well.

 

[serepton]

Thank you everyone for your replies, it really is appreciated. I imagine it must get quite repetitive with newer welders asking the same old things!

My set up is as follows;

R-Tech 160A AC/DC Tig
1.0mm Filler wire
1.6mm Ceriated Tungsten, sharpened to a fine point over approximately 5mm.

The welder is set to 42A which was the lowest I could set it to getting the puddle to start on the bottom bracket shell.

I do have a foot pedal which I have found invaluable, as soon as the puddle has started I am backing it off to move the puddle to the thinner tube and then almost pulsing it when I go back to the BB, does that make sense?

I have had some practice attempts this morning, I started out welding the thinner tube to some section that is actually slightly thinner than the bottom bracket shell but still much thicker than the chain stay tube.

Here was my first attempt;

As you can see, it did blow a hole but I found an instant improvement in the actual starting and moving the puddle, you can see on the left of the tube there is almost what you could call a fillet!

This was my second attempt;

Getting better!

I then switched to a spare bottom bracket shell which is actually slightly thicker than the shells that I will be using, this is why it is scrap.

I am really happy with how it appears to be going, it obviously needs much practice but last night I was pulling my hair out but I can see that with much practice there is light at the end of the tunnel!

One thing that I have noticed is that the shell appears to be getting very hot with the colour changing to a very dark blue. Is this just because the parts are quite small so there is not much material to disperse the heat?

Once again thank you for all of your help, I shall keep you updated!

 

[Drains]

You're getting there!

Re the heat and the blue - you're putting in more weld than you need to - the fillets only have to be sized for the thinnest material whereas yours suit the thicker. You could get away with a third of the amount of filler - the heat input will reduce accordingly.

More amps and faster travel speed may be the answer. Try putting in as little weld as possible - have you tried autogenous welding (without filler) yet? It's not what you need for this job, but it'll give you an idea of the other end of the scale.

 

[Shox Dr]

I'd also get some .8mm Mig wire

 

[serepton]

Just normal MIG wire?

I hadn't thought of that. I shall get some from the mig welder that is sat next to the Tig !

Thanks!

 

[citizen kane]

Seat tube to BB weld, this weld was a little slow with a bit to much filler but you get the idea. Keep the arc length short and move quick.