Looking at the plans by Peter Kunz at
https://www.feuerwaffen.ch/waffenkonstruktionen.htm, as well as the images of the original & several reconstructions- it seems the exact nature of the friction plate isn't well described. In only image that almost shows it is from the Rüstkammer, and there seem to be linear slots in the plate similar to that of a wheellock, rather than perpendicular cuts like a file or rasp (image below). I don't see any indication that the spring wraps around to put pressure on the bar, but it may further in. The style of rasp and its composition could greatly influence the reliability of the device, and may be why some reconstructions have been more successful than others.
