Current Projects chat and miscellany

do elaborate?

I was going to...

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 (all of which are missing on the Hope)

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*
   
   
   
   

*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.

This is the kind of design which is closest to ideal: