Where to get or how to make a bottom bracket
I have been planning on making a recumbent for a while now. I do realize that it's not quite as incredible as most of what is made on here, but I have been hit with a stumbling point. Without hacking a BB off of another bike, how does one acquire or make one? Do they make massive taps or what? I have been browsing across the frame builders section, but haven't really turned up anything concrete, so any assistance would be much appreciated.
A separate question that I thought I might throw your guy's way because of some users rather deep understanding of metal working and welding is; would there anything wrong with MIG welding a frame? Most home builders of recumbents tend to use this form of metal joining with satisfactory results, I was just curious if there was a reason that it is generally avoided in lieu of brazing and TIG? (Other than asthetics, that's not my concern, more like penetration, strength, etc.)
I only have a MIG welder so it will most likely be the route I take, I would just like to know some of the limitation of welding in this fashion.
Thanks for your time!
*edit* I plan on making it out of steel, just an fyi.
if it ain't broke, fix it
I think you'd have a hard time getting accurate enough joints with wire feed. I'd look at TIG or fillet brazing. and you can get bottom bracket shells from places like ceeway or nova cycles.
down at the bottom of that ^^^ site there are some shells, and some eccentrics, used to assure proper chain tension betwixt capt and stoker cranksets. have fun and good luck. post some pix once you get it together.
Anything can be welded any way you want. It's all down to the welder. There are three comon MIG approaches. Core fluxed wire, gas shield, both. A lot of workshop guys are set up to do the former, which other than speed has all the disadvantages of arc and none of the advantages. If you go this rooute every time you start or stop you will need to completely clean the joint.
The second is pretty good. You still will have control problems since the settings on the machine determine the ballance of heat control and wire feed. As you go around a joint you will come to different locations on the tube that will have different relative thicknesses of material, you will have difficulty dealing with those except thorugh starts and stops, and material positioning.
If you can't gas weld with your MIG you might see if there is a bottle of Mig shield gas that fits a propane torch. You could position that to shield the arc, and use a solid wire.
MIG is used throughout NASCAR (I am told) to weld 4130 car frames. It's all up to the operator.
Since you have MIG, do you have an Oxy Acet torch. For not too much you could buy a meco torch and gas weld the tubing. That's a very good process.
BBs only cost a few bucks, but you will pay to get them chased with the big tap set. You might come up with a design where the tube gets bonded into a sleeve.
people really use MIG? That I have to see. Tig and brazing are used because they are compatible with the materials used in regards to heat and material composition. There is also the matter of weight. If you use MIG, there is a fairly thick minimum wall required to avoid blowout.
if it ain't broke, fix it
I have seen wire feed used to make roll cages but they arent nascar or nhra legal. gotta be TIG. I have some friends that crewed for greg biffle when he was still in the trucks. but there's an exception to everything. For bicycles tubing i just can't imagine there's enough control for how thin some tubes are.
4130 and aluminum are comon materials so material composition wouldn't be a problem. I would be terrified of the material thickness myself, but then I don't MIG weld. I have some MIG wire that I use on 4130 at times because it is thinner than the rods they normally sell. So set-up aside it shouldn't be a problem. Aluminum bikes are often thicker wall, and there are often long welds on gussets, etc... I would almost be surprised if they weren't MIG welded. Like in a Walmart bike, there are miles of welding on some of those odd suspension bikes, that sell for real cheap. Hard to see how they would do them with TIG.
"For bicycles tubing i just can't imagine there's enough control for how thin some tubes are."
- That's probably right, but this isn't a 953 thread, or some such. Sheet metal is MIGged all the time and it's similar or thinner than a lot of tubes.
- The other assumption is that tubes have to be properly welded. There is a ton of stuff coming out of China these days that has terribly scarry welds on it, my engine crane is heart stopping (and I wouldn't buy a bike with equivalent quality welds). So far so good. I have seen welding on bikes that looked real bad but it held up fine. There is a big difference between nice welds and welds that hold up.
- Another assumption is what happens at the extreme end. Most of us aren't tour de France winners, but we still get by on our bikes. There are welders out there that are Lance Armstrongs, that push the tech, or put in really long hours to be what they are. Brad from Atomic Zombie arc welds all his bike projects, recumbents among them, using a 3/32" electrode and a basic DC box. There are always folks who will say something can't be done, and they usually haven't tried.
- There is also what the gear will reasonably do. In WWII the US had to weld tons of stuff and they had to allocate people with skills, and consumables, to the greatest needs. A lot of stuff was welded with whatever was left over. If one is ever tempted to say "that probably can't be done", one should look at some of the training tapes from that period. Almost everything was done with almost anything imaginable. Not to mention all the hundreds of thousands of airframes made and not a TIG in sight.
An interesting thread over on the 35 years or more board was a guy who wanted input on his welds done with scratch TIG and no pedal. Gotta give respect, I couldn't have done any better on my Maxstar.
a lot of the cheap bikes probably are mig, but then again they have very heavy frames. I didn't think MIG and aluminum played well together. I'm pretty sure NASCAR frames are MIG, at least that's what I've seen them doing on my TeeVee. And the motorcycle construction shows seem to mostly feature MIG, so it's not out of the question to do a bike that way. I just wouldn't want to have to push the weight around.
Aluminum can be nasty in MIG because often the wire is so soft it folds up and jams on the way to the gun. Still, they sell lots of spooled aluminum, so someone must be using it for something.
Here is an interesting article:
They mention 1.6mm as the limit for MIG. Keeping in mind that it is:
a) is what is normall, this is where the pushing starts. The TIG welding done on bikes is abnormal in a number of ways (dime spacing; fillet sizing; wire melting; surface post melt; etc...);
b) not that thick for an aluminum frame
c) Weld thickness in miters is quite likely that deep even on steel tubes, not to mention aluminum.
Another thing to keep in mind is weld geometry. This is a recumbent. I just sold my Toxy, and it had basically four joint. The frame was a bent tube about 3" indiamter. There was a miter with a BB placed forward, also oversized tubing. Massive engagement, and only pedaling loads. The bike would not collapse if the BB came off, though a crash would be possible. The second weld was where the head tube came throgh a hole drilled through the main tube. Again, massive engagement, 360 donut like welds, easy geometry, and chewing gum would almost be strong enough. The other two welds where straight line welds attaching brackets for the shock and rear fork. pretty easy again. No weird contours, large and straight.
Overall the joinery is a lot more positive. Catastrophic failure a lot less likely, and the weld lines are mostly straight and 2 dimensional. Most home projects probably won't be able to source or bend this pipe, but my point is just that this isn't a diamond frame with all that entails for the welder, there are design options and a different aesthetics that may permit more rational options.
I'm well aware of the limitations when attempting to MIG weld aluminum even with the proper set up, but thanks for the heads up. I think I will mainly stick with steel
The bike may be on the heavy end, but who cares? If it's fun to build and fun to ride, than I would consider it a success.
Now, on that Bottom Bracket Shell, I've found a few around but most are al, does anyone know of any sources in the states (that top link was excellent, but it was in the UK) that I could purchase a steel BB from. Standard threading, etc, etc.
Thanks for all the input and responses
Henry James, Nova, and BikeLugs all sell steel BB shells.
Originally Posted by Scooper
Thank you very much
The first frame I ever modified before I started building was a cheap 79 dollar nashbar frame that was a little too long in the rear. It was straight gauge 4130 and after I re mitered the rear end to fit back onto the bb and seat tube I had my neighbor mig weld it for me. He banged it out in no time and I have ridden the hell out of that bike for years and years. I'm talking wallrides, huge drops, stairs. It hasn't broken yet. I have to say it looks like **** though. and yes he welded aluminum with it as well ,he used it to repair things like flatbeds on towtrucks and such. since you are building a recumbant and you're gonna need some pretty thick gauge tubing I would say f-it and give it a shot. plus look at all of those monster bikes out there, those guys aren't tigging **** and they stay together just fine through jousting and nudity. but.......
if you have a torch you can get some brass and braze it together and it will be a much more peaceful operation. brazing is like that.........and will be stronger if you do it right.