Better quality and/or Heavy Duty Bottom Bracket Shell
 

Although the normal BB shells for sell are excellent for singles, etc., I went looking for something a bit stronger for heavy touring bike builds and for toring tandem builds.

I was pleasantly surprised to find a nice set at www.AtomicZombie.com

Part Number: BBRAC_Steel_Bottom_Bracket_2Pack_Part

Cost: $28.95 for 2 pack + $8.80 shipping ...or basically $19 each delivered.

Much thicker and better machined than most shells I have used/seen. When they arrived, I also noted threads were deep, clean and unusually well cut.

Here are pix;

http://bikeforums.net/attachment.php...hmentid=342789 http://bikeforums.net/attachment.php...hmentid=342790

Appreciate thoughts and/or other sources for building bits.

/K

my thought is that they made them thicker than usual so they can be mig welded. I have never seen a broken bb shell. I think I will stick with Paragon shells

UMan -

I didn't see any mention of making them thicker just for MIG'ing. I guess that could be a reason since they mostly support folks homebrewing lawnchair bikes, trikes, trailers, etc. Their site has some impressive photos of completely projects.

I guess we could ask Frank/Welder if MIG actually puts more heat into the weld that TIG. He would know. I have both tools, but never compared them... but I have never MIG'd anything for a bike either for that matter. I had always suspected that a TIG provided a stronger joint, but I have built frames for my street rods with the MIG and they never broke a joint...so maybe I am just muddled on that point. The availability of rod in Chromoly for the TIG is helpful for bike building.

BTW; Yes, I have used Paragon shells and much of their other build bits; it is good stuff. For the shells for some special applications, I just wanted a bit more meat on the bone and looked/found the Zombie ones. I doubt either would break even under extreme use.

/Kerry

Nothing wrong with a heavier build if the customer is OK with it. Andy.

the homebuilt recumbent crowd uses MIG a lot. In fact, there is a video on utube of a production recumbent company using MIG for some operations on recumbents. It's a matter of skill and cost of equipment for the homebuilders. You can do light sections with MIG, but it's not what most people would choose to do given the existence of GTAW/TIG. Thick wall makes MIG a lot easier.

Atomiczombie also has super-thick head tubes, probably for the same reason. The 44mm head tubes that Paragon sells are pretty heavy-duty

Older, bulge-formed BB shells were sometimes prone to failure at the tube sockets. But modern investment cast and machined shells seem pretty reliable.

Paragon has two steel BB shells. The thinner one is made of 4130 and the thicker one is 1020. I've used both and can't say I've notice any difference, but my experience is limited. I tend to buy the thicker version hoping to help mitigate warping, but whether that helps or not, I can't say.

'90, era, used the rear BB shell from the Burly Tandem frame parts , it uses an oversize sealed bearing ,
and is held in with Loc Tite and Snap-rings , square taper spindle , I fitted a M730 crank.

TIG welded on the seat and down and chainstay tubes , no holes in the shell,
so I put a Zirk in and popped out the inner seals ,
filled the void with grease , probably a half cup , so Plenty to circulate in there..

Did you have more trouble getting even heating and not over heating thin tubes when using thicker shell?

Normally the weight of the walls is a function of the tubing that was used (duh) but in the sens that if your source is say SS the wall thickness may be X or if it is 4130, or 1020 something different. Brad at AZ stick welds all his project with a fairly heavy trode.

Technically MIG would be less heat, since to make to perfect runs in either MIG or TIG, the MIG is going to be run faster, not to mention the cold start. However bike welding is difficult, and there are lots of starts and stops, controlling the heat consistently is not what MIG is good at. So you might want more beef to prottect against the spikes.

In Cars the predominace of square sections, and some redundancy you don't get in an HPV, mean MIG is a lot more efficient.

TIG allows independent control of heat and feed. This allows the operator to eliminate the cold start or too hot problems in a run, and to take the time to go just so. Inherently a weld is a weld.


It doesn't hurt that it is available, but it is not the right stuff for welding a bike, you could get by with it. Chromo rod is for structures that will be heat treated, quenched and tempered fully. Very rare process in bike building with 4130.

I don't recall any difference.