Making my own front hub, a design question
 

I am considering, only considering mind you, making my own front hub.
It would be machined out of one solid piece of aluminum. It sounds like a good project...
THe overall body would be aluminum, with a steel or even stainless steel axle.
Drilling the holes will be easy when i have the product setup on a rotary table.
My question is, what bearings should I be going for? It would suck to make the wrong choice and have a failure while on the road....
So i was thinking some good old radial ball bearings (ABEC 7 perhaps), two of them of course. A press fit on each side. Maybe im being blind at this late hour of the dayy, but i dont see much in the way of axial loads to encounter, except maybe on turns
CAn somebody help me figure out what i want to use?

The 6001 is probabably the most popular size for this application, though 6900 is also favored.

See: http://harriscyclery.net/site/page.c...ory=150&type=T

If you machine your hub shell out of a single billet, you will wind up with something inferior to even low-end Shimano hubs, because their shells are forged, not just hacked out of a random piece of bar stock.

It's true that front hubs are the easiest bicycle part to make, but to make a _good_ one calls for serious tooling costs.

Sheldon "Cold Forged" Brown

oh it wont be hacked. It will be cut on an engine lathe, and a bridgeport milling machine with rotary table.

He calls it hacking because you can't tell the grain of the stock. With a forged piece the grain structure follows the shape.

aaah, i see it.
Well doesn' DT swiss and other manufacturers machine their stuff frm a single piece? I believe my front 240 hub is.

A forged hub body is generally going to be better than a machined one. That said, a CNC'd front hub that you made yourself will be pretty cool. But I'd recommend that you overbuild it.

there is grain, it runs along the direction of the extrusion. which means that the radial strength of the flanges will ....well...be less than ideal. Find an old wooden thread spoll, notice the broken flanges? But a machined hub that you made yourself would be very very cool indeed. tack on additional safty factor and you may be fine. don't forget the spacer between the bearings. send pictures of progress!

CNC machined bike parts, including hubs, have been around for a number of years now. I don't think you have undue risk but as Timcupery suggested, error on the side of safety (make the transition zones between the flange and main hub shell fairly thick).

I once had a set of CNC machined TNT hubs with 7075-T6 hub flanges which cracked. TNT took the hubs back and rebuilt them with "new and improved" flanges made from 6061 - which is not as strong but less brittle. Based on this, I'd stick to 6061.

Yes they have and with a well earned reputation for failure. Remember all of those CNC'd boutique cranks from a few years ago? Most were made by manufacturers with a poor ratio of enthusiasm to material science knowledge and the failure rate was very high. It's not a concidence that most are out of business now.

Your point about choosing the correct alloy is spot on. Not just any random block of Al is suitable. It is quite possible to build adequately strong and durable components by CNC techniques but you better know what you are doing and use the correct materials.

Sometimes when you see something that is referred to as "CNC machined" it is actually machined from a forged pre-form. That way you get the strength of a forging with the accuracy of CNC machining.

I have hubs machined out of 7075 and I give them hell. I think the design of the hub is probably more important than people think. You can make pretty ****ty parts out of great material.
http://www.gsportbmx.co.uk/products/...0sectioned.jpg

Billet's used all the time for custom parts in motorcycle and auto-racing all the time, handlebars, fork triple-Ts and clamps, rearsets and pegs, suspension A-arms, steering-knuckles, etc. The design's more important for strength and durability than the raw material. Use Solidworks with linear-FEA and you can figure out the stresses pretty easily. Just add a little extra material on the flanges outside of the holes and you'll be fine (about 5mm should do). Be sure to angle the flanges in to aim at the rim.


Axial loads are mimimal, even in cornering. That's because you lean and loads are still radial. Axial loads would only be a issue in a trike or something that stays upright under cornering like a car.

If you really want to deal with axial loads, you can use angular contact bearings:
http://www.mcmaster.com/catalog/111/...l/6680kl1s.gif . Page 1019 of McMaster-Carr catalog

or tapered roller bearings:
http://www.mcmaster.com/catalog/111/...l/5709kp2s.gifhttp://www.mcmaster.com/catalog/111/...l/5709kp1s.gifhttp://www.mcmaster.com/catalog/111/...l/5709kc1s.gif . Page 1022 of McMaster-Carr catalog

Thats what i was thinking, not really any axial loads here. YOur weight is always sitting ontop of the hub so thats why. I've got some really nice angular contact bearings, but i think i will keep them for motion control systems :). I will use abec 7 radial bearings. no taper roller bearings.
6061 was definantly the material i would be using, i like its machinability and i've got lots of it. PLus it ahs good properties like others said

Your picture isn't much of an endorsement. That hub sure looks broken to me. :)

this is a gsport bmx hub.
more tech than you think... and itll stand up to most anyhting you put it through.

well the hub is going to have to wait...
Ive got some major overhauling to do on my cnc mill before i tackle another project