If you work on multiple bikes using any sort of bikestand, it may have gone something like this:

  1. Wheel bike up to stand. Ascertain whether you want to clamp the seat post or the top tube
  2. Fiddle with preload screw on stand until you think it will close down to around the right diameter for the chosen tube.
  3. Heave up bike awkwardly, trying to squeeze it into the jaws of the stand. If on the seattube, remove one hand and desperately try to do up clamp (top tube can be slightly easier.)
  4. After the sense of panic has subdued, re-adjust slightly and start working on bike.

Having worked on lots of older bikes (read: heavy with standard tube profiles) I thought it might be fun to see if I could devise a way to change the 2 handed clamping process often necessary. What if i could make a way of holding the bike still that used the weight of the bike itself to secure it in place?

Reading a Core77 article, I stumbled across a ingenious mechanism that could accomplish just this being used in a everyday hook: http://www.core77.com/posts/26206/linden-swedens-clever-hook-design-26206

I used this as the starting point to create the profile of a similar mechanism. In essence, once weight is placed on the lower part of the hook it pivots, and drives the top part down using a cam-like interface between the two. Initially, the shape of the mating surfaces needed work:

However, after refining the curves, and adding a number of different profiles to share the load, I was able to make something that opened and closed reliably. 

When testing this on my limited range of bikes, it proved very useful- the clamp securely held the top tube, and immediately released the bikes when I lifted them slightly out of the stand (fortuitously they all had very similar tube diameters).

Please ignore the obnoxious whistling!

Perhaps this isn't the best application when there is such a variance in bicycle top tube diameters (and shapes, given today's crazy hydro formed aluminium and carbon profiles). Any ideas for other uses?