TIG a 1/8" gap in aluminum

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Here is the situtation.  I am going to cut open an aluminum intake plenum for a car.  After I make a few changes to its internals I need to weld it back up.  The tricky part is that there will be about a 1/8" gap all the way around the part that I cut out.  The plenum has a thickness of about 3/32" that varies slightly from point to point.  The part that I am cutting out is very irregluar in shape so I must use the piece that I cut out because fabricating a new piece would be much harder.What is the best way to fill that gap back in?
Reply:Originally Posted by NazracWhat is the best way to fill that gap back in?
Reply:Right  or wrong, I have tacked a length of filler rod over the gap and then welded on that. Kept from melting a big hole and seemed to help the puddle draw the two sides together rather than have them melt away from the seam.I qualify this by saying this is something I found to work not anything I read or was taught.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:With the right choice of cutting tool and a lot of care it should be possible to end up with a smaller gap when refitting the piece. The hardest part is going to be tacking the piece back in as the arc will tend to 'dance' between the edges- laying some filler in the gap willl help get the tacks in, or you could add filler to one edge and pull it across to the other.Once tacked just keep filling the keyhole. Getting a neat root (or backside) takes some practice with open root aluminium though
Reply:Originally Posted by TimberwolfRight  or wrong, I have tacked a length of filler rod over the gap and then welded on that. Kept from melting a big hole and seemed to help the puddle draw the two sides together rather than have them melt away from the seam.I qualify this by saying this is something I found to work not anything I read or was taught.
Reply:Thank you everyone for your suggestions.  I am thinking about tacking the piece on with a few small strips of scrap aluminum.  I was concerned about burning the edges back and ending up with a big hole.  I've done that before but with the suggestions given, I think I can do this. Originally Posted by hotrodderWith the right choice of cutting tool and a lot of care it should be possible to end up with a smaller gap when refitting the piece. The hardest part is going to be tacking the piece back in as the arc will tend to 'dance' between the edges- laying some filler in the gap willl help get the tacks in, or you could add filler to one edge and pull it across to the other.Once tacked just keep filling the keyhole. Getting a neat root (or backside) takes some practice with open root aluminium though
Reply:Zip cut disk will do, but could also look at a mini saw attatchment Dremil has one ~ .025 kerf.Lincoln PT185 TIGLincoln 175 MIGLincoln 240 amp AC StickLind Needle Arc plasma welderPlasma cutter, soon???
Reply:Why don't you butter/edge build one of the pieces to close the gap up?
Reply:Agree with Supe- I would butter one side slightly with more than 1/8" buildup, fit it up and file any extra off for a good fit and weld it up.
Reply:Hmmm. Note to self; don't bridge gaps, butter edges.  Thanks Supe.  Gotta luv the internet. 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:I' m not sure what the problem is.. The base material should be more than 1/8 right? if it is that should distribute your heat well enough to carry the welds single pass. Depending on the Grade of aluminum I would use either a 345, or a 4043 3/32 filler. Some may argue my rod selections, and thats fine, just my personal prefrences. Tack it heavy so it doesn't move and toss rod till your hearts content!!! Good Luck with it. Carl
Reply:For an engine intake, I would agree with weldsupply on a 4043 filler. And Supe gave a great piece of advice. Last time I had to weld aluminum with a built in gap, I wedged in a chunk of parent material (1/8" plate, cut to 1/4" wide. I made 3 of them, used them as wedges. I tied it all together by welding up the shims, and carrying the weld back to the next one until the gap was closed. It took a LOT of filler!!And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:You should be able to just weld it once tacked securely.   Take your time and use big enough filler.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Using the keyhole technique will give the best results strength-wise.Aluminum is a little tricky to get it right though. if you can butter and edge, you should be able to work with a keyhole though.The make-shift consumable insert idea would be fine, just not very strong. This is just an intake manifold though. Unless it is a turbo car running alot of boost(14psi+), as long as you seal it it will be fine.
Reply:Originally Posted by revhardUsing the keyhole technique will give the best results strength-wise.Aluminum is a little tricky to get it right though. if you can butter and edge, you should be able to work with a keyhole though.The make-shift consumable insert idea would be fine, just not very strong. This is just an intake manifold though. Unless it is a turbo car running alot of boost(14psi+), as long as you seal it it will be fine.
Reply:Originally Posted by SupeKeyhole will work, but it's not the easiest thing to do with a square groove and 1/8" gap.  That's why I'd rather see it buttered with a slight bevel to ensure root fusion with a more manageable keyhole technique, followed up with a single cover pass.