Holding an extension spring on a lever arm

Lever arms are usually made from steel (structural) or cast iron. The second is preferred when the lever will be produced in large numbers. Is assembled with the pivot shaft and the cam through a press fitted sleeve and a cam follower with a stud and because of these standard parts has a long functional life. The only disadvantage is the spring end holder because springs are made from spring steel (stronger and harder steel). Choosing the type of spring to constantly force the cam follower against the cam depends on lever orientation and size relative to the cam shaft. Expansion springs are stronger but they need special guiding stems (extra parts). These extra parts increase the mass of the lever and the complexity of the mechanism.

Extension springs are easier in holding. Some designers prefer to provide a fixed extension end holder by means of bevel slot in a thinner part of the lever (see upper lever and details in figure above). This is a very elegant solution but it has a major problem: due to high speed movement it shall worn out and finally will be cut of from the lever. The lever must be replaced which means time to disassembly adjust and reassembly the mechanism. The second solution is to tap a thread on the lever’s end in order to bolt a movable end holder (see lower lever in figure above). The movable end holder will be replaced when it worn out without to disassembly the lever. Another advantage is that we can tap a thread in any one of the four surfaces of the lever which means that we can change the mounting position of the other spring’s end holder. When assembling the movable end holder we adjust its orientation by increasing or decreasing the bolt’s length.