Shaping Up

摘要

Figure 4 analyses the geometry of the shaper stroke.When the crank pin is set at position "b", the stroke takes place over the arc "B-B". When the pin is moved futher from the centre of the bull wheel to position "a", the stroke takes place over the longer arc "A-A". The cutting stroke is over the longer arc a-c-a pr b-c'-b and the return stroke is over the shorter arc a-d-a or b-d'-b. Since the return stroke takes place over a shorter arc, it is also quicker. Conversely, for a given stroke rate, as the cutting arc gets longer, it has to traverse a longer distance in the same time, so the cutting speed rises.