mig welding small bits to big bits

[fast_grandad]

I want to butt-weld some 16mm by 1.8mm wall mild steel tubing end-on to the periphery of a 40mm dia x 20mm thick steel boss which has been reduced to about quarter of its volume by boring out most of the centre. But its still a big lump. My 90A mig welds the tube very well but I'm concerned that I won't get sufficient, if any, penetration into the boss. Would I do better with a higher current mig or will it just blow through the tube all the time? I don't have access to a bigger welder so is there any mileage in preheating the boss with a gas blow torch?

This is a great site by the way and has helped me get back into welding after 40 years away doing other things.

Thanks

Paul

 

[peterd51]

Hi,

is it 'structural' or will it be ok if it's 'attached'.

If you have some photos then it'd help.

I'd say that if it's not something you're trusting your life to then you'd get away with pointing the torch at the thicker bit and letting the weld-pool melt into the thinner bit.

It'd be like a circular fillet joint I guess?

Regards
Peter

 

[fast_grandad]

Hi Peter, thanks for the reply

It only needs to be attached. I certainly wouldn't trust my life to anything I'd welded just yet! Its a wing stay for a race car so it needs to be secure but isn't under any great stress other than a bit of vibration.

I've tried what you suggested and it does seem to work and looks and feels pretty secure. I'll try and post a photo or two in the next day or so.

If I get a reasonable result with this I can see me investing in a higher current machine. 90 Amps isn't really enough for anything too serious. I've added the two recommended wire feed mods for SIP MIGs, the separate transformer and the support for the roller, and its transformed the machine.

Thanks again

Paul

 

[Hitch]

As has been said above, run the weld on the boss, then just edge it onto the end of the tube as you go around it.
Do a few practices to get the hang of the joint