Replacing the shear pin on TOS Trenčín SN lathes

The shear pin is a simple but essential safety component used on TOS Trenčín SN lathes. Its purpose is to protect the thread cutting gearbox, leadscrew and feed mechanism from damage caused by overloads or accidental crashes. When the pin breaks, the machine may suddenly lose feed or threading capability even though the gearbox appears to operate normally.

In this guide we explain how to identify a broken shear pin, locate it on the machine and replace it correctly on SN40, SN50, SN63, SN71, SN400, SN500, SN630 and SN710 lathes.

The lead screw (9) fig. 4.8-1 is secured with the shear pin 806151 (10). When the maximum permitted feed force is exceeded, the pin is cut and the connection between the lead screw and the thread gear box is lost. For replacing the shear pin, release a snap spring (11) and move away a ring (12). When the drive is disengaged from the feed rod, the gears are protected against overload by an apron protection system.