People who have been following the discussion on preventing roll
slippage may find it interesting to see all the articles that have been
written and stored in the MMD Archives; look under Brake and Brakes:

  http://www.mmdigest.com/Archives/KWIC/B/brake.html 
  http://www.mmdigest.com/Archives/KWIC/B/brakes.html 

Just to summarize my own position, I feel that it is impossible to get
a properly adjusted brake that will work with all lengths of all papers.

I made a variable friction mechanism that is under its maximum friction
with a fat roll that goes up to the edges of the flanges, but as the
diameter of the roll gets smaller, the friction also lessens.  This
allows me to play even the largest rolls with no slipping, and if
I grab the cardboard tube, the wind motor immediately stops.  This
shows that the brake is not too loose.  I could send a picture if
anyone wants.

Randolph Herr