[nova_70_383]

guys that have tig'd 1 5/8" dom tubing for roll cages... what size cup do you like to use? 3/32" electrode and 3/32 70s2 wire i assume? tell me what you like to use. thanks

[noddybrian]

Hi - this is more personal preference - but I Tig tube in this diameter range reularly & my choice is a gas lense with a No.7 cup as it's easy to lose gas cover due to torch angle depending on joint shape - this also allows long stick outs if needed where tubes join at difficult angles - if this is too bulky for a given job I'd use a standard collet body with the smallest cup I can get away with for the current - normally a No. 5
Hope this helps.

[nova_70_383]

yes it does help thank you! 3/32 rod would you agree?

[noddybrian]

Yes- I'd say 3/32 is the most usefull size for you - the wall thickness you likely have suits this fine - only time a thicker ( say 1/8" ) rod helps is when you have less than perfect fit up of joints - the thicker rod cools the pool quicker so it's slightly easier to fill a gap & not have burn through - obviously the better the fit up on tube work the better it looks - although on roll bars it is quite accepted to have larger welds to spead the stresses at joints - I've just made up an arbour to fit my vertical mill that lets me use " Rotabroach " cutters - these are so much better and more rigid than hole saws it leaves a real nice job on notches.
The 70 S2 should work fine for you on most common DOM tube - though I have had some strange materials of unkown spec when the customer has " procurred " it themselves ! & I'm guessing they can't go back to source & ask what it is !

[nova_70_383]

this is mild steel, not moly so i know its mild steel. fit up on a roll cage is important wide gaps are not acceptable in my book. heres another good question. lets say in a hard to reach place you opt to use a 1/16 rod, and weld real slow. is this going to be a bad thing of more heat being put in? maybe lack strength? i have never done this on round tube in this application, but have welded other things with too small of a rod in non critical apps... whats your thoughts? id like to know for future reference.

[noddybrian]

MY thoughts on that really are why would the situation arrise ? I would normally pick tungsten size based on current range / thickness of material & therefore by rule of thumb the filler rod would normally be the same diameter - if the roll cage is all the same material once you have a rod & machine setting that suits why change it ? the slight change in rod diameter is not going to improve access on shallow angle joints enough to make much difference - the best solution to this is when possible is to come to a compromise on design that allows viable weld joints - even if this means adding an extra slight bend in the tubing from being in a dead straight line. As the material is mild steel you can afford to take your time welding - your not going to significantly alter it's stucture with heat - the only reason it seems stiffer than regular ERW tube is the forming processs causes a slight work hardening effect - if it were an aircraft frame or other high stress / light weight frame then I'd worry - most roll cages are built without too much scientific testing based on hoe the customer thinks it " should " look - & are generally overkill - except maybe rock buggies that mount suspension parts to them them - a cage is only ever as strong as the floor parts it's mounted to.
All the best with future projects.