tips for welding small aluminum bosses?

I'm TIG welding a short section of 1/2" diam aluminum rod into a hole in 1/8" aluminum plate (which has already been welded to a piece of tubing). A hole
through the rod will be taking a lot of force, and the weld bead will help transfer the tension side of the force to the plate. I'm having a lot of trouble getting the heat where I want it and keeping the weld bead small enough; it seems like once I get enough heat to form a pool it just wants to climb right up the side of the rod. Here's a couple photos that show the situation (force direction is from right to left):
http://mysite.verizon.net/vzeqn3w8 /
Does anyone have any tips for small things like this? I'm using sharpened lanthanated tungstens which gave me a huge improvement in controlling the arc, but the combination of the inside corner of the joint and the outside curve of the boss is giving me fits. Would heatsinking the boss (with a large piece of copper or something) help?
For a while I decided to give up on welding this part and to just braze it in, which seems to work ok with HTS-2000, but I'd really prefer to not add another process if I don't have to, so I'm back to trying to weld it.
Thanks!
Mike
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the small aluminum bushing (1/2" rod) is getting hotter than the 1/8" plate, you're on the right track with heatsink. can't tell from the picture how much aluminum mass you have welded on the other side of that plate.
either preheat the plate or heatsink the bushing (try tightening a nut/bolt through the bushing.. maybe with a stack of washers on each side -- dont squeeze too tight, or use too loose a bolt, as the bushing might give when heated).
or weld the bushing into the plate before welding the plate to the other aluminum piece.
you could try countersinking the hole to 1/2 thickness (or more) of the plate. once the bushing is inserted you'll have a nice tight V-groove to help control the puddle width. turn your freq way up if you have the option, it'll keep your arc tighter.
Mike Vande Weghe wrote:

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Your problem is not unique to you in any way , have been TIG welding for more years than I would like to count , pictures seem to show that you are getting more or less sufficient heat input to the joint , no heat = no weld , if you could leave a little more of the 1/2 in. rod come through and trim it off later , it would help , anytime you weld close to a sharp corner like you have on your rod , the corner has almost no ability to withstand heat , in other words ,no heat sink , a very proficient weldor with his machine skewed mostly toward the negative and perhaps 75% helium and a smaller tungsten could probably make it work , even welding done in the aircraft industry sometimes requires a little re-design of a very troublesome joint , Good Luck Phil

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Why not try a smaller tungsten and lower temp rod? Also might be worth drilling hole in rod part, before you do weld.
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Thanks for your tips. I had another go at it and got some much better welds this time. I started by trying a 1/16" lanthanated tungsten instead of the 3/32" I had been using, and it held up pretty well to the approx 120A I was putting through it. I also tried to really focus the heat into the plate and not worry about applying any heat to the boss. What I discovered, almost by accident, was that it works much better with the torch perfectly perpendicular to the plate. Instead of trying to direct the arc into the joint corner (which overheats the boss) and slightly in the forward travel direction (which doesn't work well because of the tight curvature of the boss sidewall), I just pointed it straight at the plate. Once you get a pool started, the boss stays plenty hot and the pool readily climbs up the side, but this time only about 1/2 way up, the way I wanted. The plate shows much better weld penetration. The final thing I discovered (again) is that with aluminum you can't be afraid to really pour in the heat. It seems like I always get better results if I trust the current setting, floor the pedal, and move quickly, as opposed to being tentative and trying to "creep up" on the right arc current.
I didn't end up trying to heatsink the boss, and with my technique of directing the arc into the plate I don't think I'll need to.
Thanks again for your tips and encouragement.
Mike
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wrote:

Thats exactly what I do. Not sure if its the proper way...but when I try to creep up on it..aluminum tends to slump and fall out leaving a hole...and set my pants leg on fire...sigh...
I usually set my % of arc start at least 50% so I dont get nervous and fumble around. It forces me to work fast.
But then, Im only a dauber.
Gunner
"If thy pride is sorely vexed when others disparage your offering, be as lamb's wool is to cold rain and the Gore-tex of Odin's raiment is to gullshit in the gale, for thy angst shall vex them not at all. Yea, they shall scorn thee all the more. Rejoice in sharing what you have to share without expectation of adoration, knowing that sharing your treasure does not diminish your treasure but enriches it."
- Onni 1:33
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