For folding sheet layers the folding blade (20) forms a comb. The comb gaps (27) are closed during fold pressing and opened during transfer of the fold to a conveyor (21). Thus the conveyor (21) engages the sheet only in the region of the comb gaps and easily withdraws the sheet without pressing it into contact against the folding blade (20). For controlling the gap variations a fully mechanical cam control (30) is provided underneath the working plane (10).
In a booklet maker or sheet folder wherein one or more sheets are pushed through a nip formed by a pair of crease rolls, and wherein the crease rolls are driven by gears, a slip clutch is operatively disposed between one of the crease rolls and the gear driving the crease roll. The slip clutch compensates for the abrupt change in frictional coefficient experienced by the crease rolls when one or more sheets enter the nip.
