The invention relates to a method of making nipple holes or similar holes in a double-walled wheel rim having an inner wall positioned radially inward and outside of that an outer wall. The holes are made by punching by means of a punching tool provided with a cutting edge whereby the cutting...http://www.google.com/patents/US5829299?utm_source=gb-gplus-sharePatent US5829299 - Method and apparatus for making nipple holes in a double-walled hollow wheel rim of a spoke wheel 
