Fork design

[The_Break]

Hi Guys

 

Need some help please. Busy with a special bike design and need to do some strength calcs to check forks will do the job safely and need to get some measurements.

 

Does anyone here have a fork with an alu steerer and a vernier to check what the steerer tube wall thickness is?

If you can also list the fork name and model I can then check which material it is an get some basic figures for my calcs.

 

Thanks,

The Break.

[Vinnydabutcher]

The irony in your name vs what you are planning is great!

[The_Break]

The irony in your name vs what you are planning is great!

 

Hehe, now that you mention it, it is rather funny.

[droo]

28.6 OD x 2.0

[The_Break]

28.6 OD x 2.0

Thanks Droo. What fork is that?

[The_Break]

Anyone else out there with an alu fork and a vernier?

[droo]

Sorry, only read half the question... Fox Vanilla 2007 and an old Rockshox Duke, both alu steerers.

 

Happy building...

[The_Break]

Sorry, only read half the question... Fox Vanilla 2007 and an old Rockshox Duke, both alu steerers.

 

Happy building...

 

Thanks very much! I am guessing that because most lugs are pretty standard OD that most forks will be 2mm thick. All of the carbon forks I have are also 2mm thick.

 

Anyone with road forks?

Edited August 11, 2012 by The_Break

[deanbean]

RS Sektor alu also 2mm.

[Johan Bornman]

To manufacture a fork steerer with 2mm aluminium (or even steel) would be big mistake.

 

Steerer tubes are part tapered. The end that presses into the crown is usually 5.5mm thick and that tapers down to 2mm over the first 150mm or so. Then it evens out to 2mm up to the stem end of the steerer.

 

The alu is usualy 6000 series and my guess is you'll have to take what material is available.

 

Should you calculate the strength for a 2mm steerer, it would be strong enough (not durable enough though) but the flex at the crown would quickly destroy the bottom headset bearing.

[Cav']

Listen to Johan, he know's his ****

[The_Break]

Thanks. Will check this out. I would think though that the taper from say 5.5 to 2mm would be less than 150mm to cater for the shorter headtube such as on the 48-51cm bikes?

[Johan Bornman]

Thanks. Will check this out. I would think though that the taper from say 5.5 to 2mm would be less than 150mm to cater for the shorter headtube such as on the 48-51cm bikes?

Yes, 150mm is a guess. I don't have a new, naked fork here to figure out how far the taper extends. But I am sure you'll be able to do the calculations required to restrict the bending moment at the bottom bearing to a)under the material's fatigue limit and b)to prevent fretting damage on the bearing races. With any reasonable material such as CroMo, 600X or 700X alu, I doubt the length of the taper matters as long as it is extends just a bit further than the bottom bearing's location. Manufacturing such a steerer from scratch poses some challenges for the average Joe and indeed even the average machine shop. The taper is internal and will require a long, thin boring bar ont he lathe. I also happen to know that the tube has a flange at the bottom that prevents it from pushing through the crown. In other words, it is inserted from the stem end and pressend until the flange sits flush in its recess in the crown. This ridge prevents accurate meaurement of the bottom tube section.My 5.5mm guess takes into account a 0.5mm flange. Edited August 11, 2012 by Johan Bornman