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I need a seat clamp of unusual size.
GF's Chinese carbon 29er has a 31.6mm post. It's had a PZ Racing 34.9mm clamp for about 3 years but the threads on the bolt have failed. I measured the clamping surface again to check as I suspected the clamp was close to bottoming out.
The clamping surface has a diameter of 34.5mm, 12mm tall.
I've only found one option better than another 34.9mm-nomimal clamp, that being Miche's clamp on which is engraved "D34,6-35". I've never seen another clamp quoting a range, so this pleases me, but not as much as if the range covered the diameter I have.
Any suggestions?
Emyr-
Any suggestions?
Get a 34.9 in a #tester_approved pattern and some 0.2mm/0.008" shim stock. This is literally the best place on a bike to use a cylindrical shim, since it has no loads to take except the radial compression
gbj_tester
This is copy-pasted from the current projects thread:
The purpose of a band clamp on a shaft is to create a uniform circumferential tension in the band in order to generate a uniform radial pressure on the shaft. Anything which tends to disrupt his uniformity is a bad thing. Taking this into account, the tensioning device should as far as possible pull in a direct tangent to the band, and the band should have as little resistance to changes in diameter as possible consistent with having enough tensile strength to resist the circumferential tension. We can approach these ideal conditions witht he following design elements
1.Pivots for bolt the bolt and nut elements of the tensioning device, to align the thread for the best tension per tightening torque and to give the best approximation to a true tangential pull
2.A thin and uniform radial thickness on the band, to minimise resistance to bending. To achieve the required tensile strength in a thin flat band, the material should be chosen for high tensile strength per unit area, so carbon fibre with the fibres running mainly circumferentially or high tensile steel are good and aluminium alloys are very much a second best.
3.The axis of the tensioning device as close as possible to the axis of the shaft, which implies using the smallest bolt which will generate the required tension. A high strength (12.9) M4 bolt is big enough.
It's not rocket science*
This is the kind of design which is closest to ideal:
*It is rocket science. The Marman clamps used for interstage coupling meet the criteria above, although they then use a second inclined plane element (V-groove and tapered flange) to further convert the radial pressure into an axial clamping force.