Abstract: In apparatus for converting tape roll stock into narrower roll segments, and which includes a rotatable cutting blade and means for automatically advancing the blade to engage and cut a revolving roll of tape and means for retracting the blade between sequential cutting operations in a repetitive process, a clutch mechanism for locking the blade on its shaft against rotation during initiation of entry of the blade into the roll stock, thereby to avoid adverse effects such as nicking and double cutting due to lateral runout of the cutting blade edge during blade rotation.