The dial, therefore, would enable the carriage to be engaged with the lead-screw at points equal to a travel of one-half inch.
The 24-tooth gear goes on the spindle stud and, the 40-tooth gear on the lead-screw.
If, on the other hand, no movement takes place, it is an indication that the pitch of the lead-screw is correct.
As previously explained, lead-screw S is only used for feeding the carriage when cutting threads.
The carriage should not be disengaged from the lead-screw after starting the cut, the tool being returned by reversing the lathe.
Suppose that nine threads to the inch are to be cut and the lead-screw has six threads per inch.
This is not the case, however, when the number of threads being cut is not a multiple of the number on the lead-screw.
By referring to the last column, we find that the lead-screw gear should have 84 teeth.