making a bmx bike frame.

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hi,im thinking of making a bmx bike frame, im going to be using a 85enb mig welder and making it from steel tubing. my question is MIG as strong as TIG all i can find is that TIG is much better looking, also when i googled it on bikes it just shows road bikes im going to be doing jumps and stuff that will casuse stress on the frame do you think mig will hold up im only 14 so i wont way 100 pounds.thanks-Ryan
Reply:well that depends on how good your welds are not so much on mig/tigChuckASME Pressure Vessel welder
Reply:Hey Ryan,Mig is a perfect process for welding bicycle frames.  I wish that I had one in 1980, when I was 16 and got a deal on a sweet Torker frame that had the seat tube partially separated from the bottom bracket.  My dad and I reinforced it and brazed it, but it just couldn't hold up to my weight (I was a big lad- 180 pounds!)  I think a well executed MIG weld would have been perfect!Just a heads up, however; frame building can be tricky.  The various diameters of thin-walled tubing welded at various angles mean that you have to be careful with fitments and then welding.  The bottom bracket has 2 large tubes (seat and down) and 2 small tubes (chain-stays) that all come together in a small space.  You have to think about the order that you will weld tubes,  in order not to block your ability to fully join each tube.  On top of that, those small, thin tubes like to move when they get hot.  Most tubes can be cold set, if they move during welding, but try to reduce the amount of cold setting by using a jig or fixture of some kind (MDF for one-off work is fine, just keep a damp rag handy for the obvious).  Also, use tack welds, to minimize movement.  If you can find a few old frames, get'em, cut'em, and practice with'em before you start your main project.  Are you going to cannibalize another frame for tubing and axle drop-outs? Keep us postedhave fun,cricman
Reply:cricman´s got it!My Babies: HF Drill pressHF Pipe Bender3   4.5" Black and Decker angle grindersLincoln Electric PROMIG 175that´s it!
Reply:yeah ive been looking at building a bmx frame for about a year i know how to build them ive asked solid bikes and they explaind it i also took an online shop tour of how to make bike frames at FBM. i dont understand if mig is so good why do they use TIG on all the bmx frames?  im probly going to buy the head tube (intergrated style) the bottom bracket will eather be euro or mid im not desided yet and the dropouts will be orderd from solid aswell.im going to probly get started on a jig tommorow. i have about 27 dollors cash would that cover the cost of some mdf for the jig?thanks-Ryan
Reply:is there anywhere i can find a good picture of a bmx frame jig? im looking for a wooden one as its probly going to be a 1 off frame ive googled it but found nothingthanks-Ryan
Reply:Google recumbent bicycles or hpv bicycles for  jigs.  There are many jig designs on the net though not specifically for BMX.I have built several bicycles.  My last one I built vertically.  The jig held a bottom bracket and the rear dropouts. I liked that approach.  It was a recumbent bicycle, however.  The first frame, a track bicycle, I built flat on plywood. I actually drew all of the tubing onto the plywood then placed the tubing above the drawing.  I also drew the rear wheel on the plywood.I have brazed and migged my frames.  Tig would offer more control than mig.   I do believe most department store frames are migged welded.  Practice much. Spend much time of the jig and building will be easy. You can do it with mig.  Good luck.  Go to your local home center and look for damaged 3/4"mdf or 3/4" inch, plywood.  Get it discounted. You won't need more than 4'x4'.
Reply:yeah thanks. the only thing is most department stores arnt for doing this my only concern is that MIG wont hold up to the stress. department store bikes are more for hoping of curbs, racing and riding arpund with mates.thats for link though!also do you think mig will hold up to the stuff thats on the vidio?thanks-Ryan
Reply:Here's my take on it Ryan...For the type of riding you want to do, weight is a big issue with the frame. The majority of the frame manufacturers are using thin wall alloy tubing. This saves weight but requires TIG welding due to the alloy content and thin walls of the tube. If you are not too concerned with the weight of your frame(s), then building them with regular, thicker walled mild steels and MIG welding will be fine but not ideal for the type of riding you are doing.I build on-road and off-road race cars with mild steel tubing and MIG welding all the time. They can take abuse very well as long as the design is proper.- Paulhttp://all-a-cart.comWelding Cart Kits and accessories
Reply:ZTFab is spot on.  You'll have a slightly heavier frame, but strong enough for your weight, and then some.  If you watch the video closely, the rider (quite skilled, obviously), with only a few exceptions, mitigates a lot of the force exerted on the bottom bracket and head or steerer tube by being smooth on landings.  What's he weigh, 7 to 9 stone?  No doubt the forces exist,  but because they are spread over a longer moment, the tubing tends to bend before welds or tubes break.  As for the wood; do some scrounging, if you are resourceful, you should be able to round up what you need for free (after asking!).Some people do the front have flat, and then tip it up to add the chain and seat stays, while others do all flat or all vertical.  The way you decide is the best.  As for the design, if you have access to a frame with a geometry that you like, or is close, get it and make a jig around that.  There is little re-inventing of the wheel left for steel BMX frames, so go with something proven, and that you think that you can accomplish.cricman
Reply:Ryan,It's not so much that a MIG weld is better or worse than a TIG weld, it's a matter of using the appropriate design, materials, and processes for the job.TIG welding is used on the thin wall tubing, because it is the appropriate process for that material.  The thin-wall tubing was used in an appropriate design, so the whole 'thing' comes out well.MIG can weld the appropriate materials just fine.  It just doesn't usually have the fine level of on-the-fly control that TIG with a foot pedal can do.Use the appropriate Design, materials, and processes.  The best weld in a poor design with poor materials will still fail, same as a poor weld with good materials but a good design, or a poor design with good materials and welds.
Reply:Ryan,Are you going to purchase a tube set or are you going to take parts from another frame? I purchased my tubeset for track frame form Nova cycles at Rocklin, CA.  I am sure there are suppliers in the UK.  Reynolds bicycle tubing is made there.  Though one needs to be approved to purchass some of the Reynolds tubing.  Tubing for bikes is purchased in rough size of the rider, then cut to specific fit.  It is important to have to appropriate size frame because often you can purchased butted tubing.  Butted tubing is thicker at the ends.  Order the wrong size tubing and you cut away the butting.
Reply:Hi, I just found this forum the other day, wanting to research TIG welders for this very thing. I build bike frames full time, although now I'm doing as much frame painting as framebuilding. I use lugs or fillet braze, but may want to do some TIG. Go to http://www.frameforum.net. There's been a few discussions about TIG vs MIG on bike frames.  There's also a framebuilding mailing list where this has been discussed before. Do a search for framebuilding list and you might be able to find it. I don't look at the list and forums very much as my workload is always too heavy.  Good luck with it.
Reply:A BMX bicycle frame? As a first welding project?  Isn't anyone else concerned about the safety of this endeavor? I'd suggest learning to weld and then practicing... for a while... before attempting to build a bicycle frame.
Reply:I didn't read anywhere that this will be Ryan's FIRST welding project. http://all-a-cart.comWelding Cart Kits and accessories
Reply:i just bought a $1500 mountian bike (high end) that comes with a aluminum frame all tig welded and i have punished it and there is no signs of cracking or bending.I would say go for the tig it is slow but that way you can take your time
Reply:Originally Posted by sstorkelA BMX bicycle frame? As a first welding project?  Isn't anyone else concerned about the safety of this endeavor? I'd suggest learning to weld and then practicing... for a while... before attempting to build a bicycle frame.
Reply:nah ive been doing loads of welding on sheets of steel and welding butt joints and stuff ive been welding about a mounth or so i think im getting good ill post some pics in a while.-Ryan b
Reply:Originally Posted by steve28what better way to test your welds then putting them to the test in the real world!!
Reply:Most steel bicycle frames are brazed, not welded.  Some brazing alloys have tensile strengths in excess of 110ksi, much stronger than the steel itself.
Reply:Mig/Tig welder steel & aluminiumI would TIG it up. You have a little more control over the depth of weld as you navigate/weld around the tubes. You will have a better opertunity to stop and move your TIG hand set and start again without showing any sign of having stopped at all.Most MIGs take a lot of setting up to get a perfect looking weld on small areas like BMX frame joints. With lots of MIG practice it is acheivable but not for your average OK welder without lots of time spent welding that shape and material.A good standard of TIG weld can be acheived that will perform and look great as you practice your style you can create a large weave or a tight smooth as a MIG run of weld.It will be down to how well you can set up the weld unit and weld in the end I think, as tig and mig will offer good results to a compitent welder. Steel or ally.I would Tig on the grounds that I consider you would have greater control over your depth and speed of weld as small TIG handsets can be so easy and versitile to direct around a BMX frame.Good luck.I'm just about to alter my frame design so may be I can tell you more in the months to come.John
Reply:Just a note on the practice time. A month or so will not be enough. I have welded 7 hrs a day 5 days a week for 6 years and I know I can do it but most people should take more than 2-3 months solid welding commercial experience before putting a life in your hands as a welder, welding up a BMX frame that you can actually use as a BMX bike and not a trophie.
Reply:I would say find some one close to you that knows there stuff with welding. Build your frame tack it up. Tak it to him make sure the design is good (if its not the best weld in the world wont hold). Then weld it take it back and have him check your weldsWeldandpower 225Heliarc Rig for itTorchesect ect ectLifes Short WELD NAKEDLooking for a SA200
Reply:Since this original post is about 3 years old, one wonders how the frame held up.
Reply:Back again with my updates. I have my first frame........ see www.insanebmx.com for the details. You can now purchase a mid BB and intergated cnc head tube from me. have a look at my INSANE BMX DESIGN.welds look a little hot. Your down tube could be higher on the head tube as well. putting it that low sure makes it easier to get to but it will certainly take a lot of post weld machining to get your integrated headset to work properly. I've built about 10 frames and learn something new on every one.