O/A welding Aluminum?

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Hey all, this forum is just awesome!  So much info to read.  What I'm not finding through search though is the reality of welding aluminum with O/A....Now, let me back track.  I'm an artist type with a little handyman mixed in and I'd like to get my own welding setup.  My brother likes the idea too and we want to chip in together to buy the equipment and share.   The thing is he's got a project in mind to make his own bicycle and wants therefore wants to weld aluminum for the frame.  He says, lets go stick welder (flux arc setup) so it's easier to weld aluminum.  BUT, I like O/A better for bending, and welding.  We both have very limited experience in welding - he's done both O/A and stick, I've only done O/A.  He's maybe 7-10 years out of practice, I've only used a torch for maybe 7 hours.  So, can I convince him that he can weld his aluminum with O/A?  I read a thread or two about a Henrob, but that's out of my price range.  could he use a 0 or 00 tip with low pressure and maybe some "heat syncs" to be able to weld a bike frame?  If not, how well would a "gas-less MIG" (a MIG welder that would later get it's gas when we can aford a tank) work?  I've read some people saying it's great welding I never use anything else, but turn around and hear how people hate to use it on aluminum.  Oh yeah, this is going to be light weekend hobby use only- nothing serious.  I'm thinking I might just rent the tanks when we have projects lined up rather than investing in owning (at least at first).  I think that's it.  Thanks again for all the great info here, and the cool project ideas!
Reply:I don't think I'd use O/A or stick for a bike frame.  I'm picky about the way the welds look on my bikes.  Also, considering you mentioning that you both have limited skill. I'd say a MIG -Gas Metal Arc Welding for those of you who are picky .The process is easier to learn.  Plus it makes good looking welds.Edit: Also, I don't know if it's necessarily easier to weld alum. with stick......Last edited by DubJ; 09-05-2007 at 01:16 AM.***Stick welding like, woah.***
Reply:O/A welding an Aluminum bike frame would take some serious skills.  As for stick welding it, I've never stick welded Aluminum but, from what I've read it would be beyond difficult to do.  A/C TiG would be best but, MiG would also work.  Either way, you're going to have a lot of $$ invested to do Aluminum.Make it out of Cro-Mo, you can O/A weld that relatively easy.
Reply:I have done both stick and o/a on aluminium. Both processes require much cleanup.  I wouldn't recommend either process for a bicycle.  Are you going to use bicycle tubing or scrap aluminum?  Stick aluminim is easy.  However it would be an expensive venture. I don't know how less than 1/8" material would weld.I think the biggest problem with thin aluminum is the volume of heat required to get fusion.  Small tips are not necessarily what you want, perhaps you will want multiple torches.  You will need a way to keep the heat from wicking away othewise you will be waiting a while to begin welding.
Reply:Thanks for all the great replies!  The funny thing is that the replies I'm getting aren't clearing up the answer!     I'm sure his project would be using bicycle tubing - he wants it to look good and last for a long time.  Here's the thing I don't understand.  Why would I want a bigger tip or two torches to do aluminum.  As I understand an O/A tip will put out something like 5k degrees at the hottest part of the fire.  Aluminum melts around 2k degrees, so wouldn't a bigger torch or two torches just add twice as much risk of warping or turning the tubing into a big puddle on the floor?  Wouldn't the ideal situation be a small controlled point of heat and a method to stop the heat from transferring too far since aluminum is so heat conductive?  If the O/A torch has way more heat than you'll need to boil away aluminum, then why not just keep the heat localized?  Also, what makes MiG better for this - besides the shielding gas for pretty welds?  Doesn't that process achieve the same temps or more than O/A? Sorry for all the questions, but for me I have to understand the technical behind the process so I know what's going on when I try it out.  Haveing a background in the process let's me figure out or deduce what's happening when things go wrong.  Thanks again.
Reply:OA welding aluminum is marginal at best, stick welding it, especially on saddle joints like you'd have on a bike with thin material, is extremely difficult to do.  The entire project sounds like a disaster waiting to happen from a safety standpoint.  My $.02, buy a used TIG machine.  This way you have both stick and TIG welding capabilities, and there is little that can't be done with those two processes, including his bicycle frame, and if you're sharing equipment costs, something like a Synchrowave can be had for a few hundred dollars each and will last a lifetime.
Reply:Like you say, aluminum is very heat conductive. If you use a small tip, the aluminum will conduct heat away as fast as you can put it in and you will end up with a hot part(s) and no weld. You need to get the metal melted quickly before the aluminum can suck the heat away from the weld area. That is why MIG and TIG work well on aluminum because they both concentrate intense heat in a small area allowing the weld to be made without a huge heat affected zone. Aluminum also oxidizes quickly, especially when heated, and the oxide melts at a significantly higher temperature than the base aluminum metal allowing the base metal to liquify before the surface oxide melts (aluminum puddles on the floor). That is why both MIG and TIG use an inert gas to remove oxygen from the weld area. O/A relies on a flux to clean off the oxide and prevent oxygen from getting to the metal. It's messy and makes it very difficult to see what you are doing because of the bright flare it creates when welding. If what you want is a homebuilt bicycle frame, you will be money ahead to make a fixture to hold all the parts in place (which you will need anyway even if you weld it yourself) and fit up all the parts at home. When you get everything fit up and held in place the way you want it, take it to a weld shop that does a lot of aluminum work and pay them to weld it up for you. It will be far cheaper than buying a welder suitable for aluminum and paying for all the aluminum you will need to become proficient at welding the stuff. Unless you are building a really unique bicycle, you could buy a comercially built frame that would be lighter, stronger and cheaper than what you could build from the point you are at right now.Just my $0.02JimCut an MGB and widened 11" C4 Corvette suspension and LT1 Chevrolet power & 6 spd. Pictures here:Part 1http://forum.britishv8.org/read.php?13,7581Part 2http://forum.britishv8.org/read.php?13,22422
Reply:Don't try to convince your brother to go with o/a.  I have never heard of anybody gas welding a frame.  I have made 3 steel frames and done research.  Perhaps you can call Reynolds Al.  I have a book by alcoa that shows o/a on aluminum.  Those guys made really nice welds using o/hydrogen.  Perhaps Cannondale can help, also. Try it and let us know how it turns out.
Reply:Matttail,Not trying to rain on your parade, but, based on the questions asked, I have to believe that with your current expertise level, there is NO process which you can use to fabricate a bike frame.There is a guy (Aerometalworker) I believe, on the Miller Board who has done a lot of aluminum work with a torch.  He recommends a Hydrogen/Oxygen gas.  Regardless, building a bike frame with a torch will require an extremely high level of proficiency and training which you don't seem to possess.Stick welding aluminum this thin will, I fear, be an exercise in futility.Mig welding aluminum this thin will also be a serious challenge.  To do it properly (still difficult) would require pulsing, which most entry level machines are not capable of doing.To me, your best option, would be to purchase a small Tig welder.  It will have to have AC capability.  I'm thinking something in the TA 185, Lincoln 225, Miller Syncrowave 200, Miller EconoTig, etc range.  A Miller Dynasty 200 would be great, but likely out of the price range.  Then, it comes down to a matter of practice, practice, and then more practice.Bottom line.  There is no "easy/quick" solution.  If all you're talking about is fabricating one bike frame, you'll be money ahead to just buy one already made.  The welds you're talking about are not easy for a "newbie".Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:thanks for the explanation Jim that helps a lot. What's the weight difference between Aluminum that would be used for a bike frame and similar Chrome-moly?  I'm thinking we go with a O/A setup for it's wide range of use and inexpensive setup, and use chrome-moly for the frame or have it welded for us.
Reply:Thanks sundown, that's what I was beginning to think.  Once I finally get a setup I'll have to buy some scrap aluminum and see what happens just for kicks.  Seeing as this is only one project idea, and the main use will be more general use I don't see the point in investing in a fancy machine just for one idea.
Reply:Use chrome moly for the frame and braze it instead of welding.
Reply:Al  is about 60% the weight of the same vol of steel.  But the design for an Al  frame and a steel frame are a bit different so an exact comparison is difficult.  CroMo is more forgiving than Al.  Easier to weld & braze as mentioned here.  Less prone to embrittlement.  Steel frames have a nice springy quality while Al tends to be unpleasantly stiff unless the bike has suspension.  Finally if the bike wrecks and the frame bends, steel can be pulled back into shape while Al will fatigue if you try this.  Some framesets come with close fitting lugs that can be silver brazed/soldered.  This construction is very strong and the brazing is quite easy to do.  It is also a comparatively low temp process and will have the least effect on the heat treat properties of the CroMo tubing.355# Hay Budden3# Hofi HammerPropane ForgeIdealarc TIG 300/300AllStates Oxy Propane torchSmith Little Torch