The reeding is produced at the moment of the strike, as the coin expands and meets the collar. The collar has ridges that create the reeding. The planchet has a low "proto-rim" which assists in the formation of the "design rim". The latter is produced during the strike as coin metal rises into the rim gutter in the die face. So a weak strike will show little or no reeding (the coin fails to expand sufficiently to meet the collar) and the design rim will be poorly developed or absent (coin metal fails to rise high enough to fill the rim gutter.