How is the pitch of screw threads measured?.
The thread pitch can be measured with a steel ruler, or a caliper or comparator can be used. The thread pitch is the axial distance from one thread groove to the next. By laying a steel ruler down the axis of a screw and counting the number of thread crests in a given length. A common mistake is to count the number of threads starting with "one". This will lead to a one pitch error. Make sure you start with "zero" for the first thread. To double check your pitch determination, check your pitch determined by count against your actual pitch measurement.
2. What is the difference in profiles between metric and imperial threads?.
Imperial threads allow sharp roots in internal threads, which is perfectly reasonable as there is no risk of material failure in this area from a stress concentration. Metric threads allow for flat bottom external thread roots which is also perfectly reasonable as it must be accompanied by minimum blend radii thereby minimizing the stress concentration in the screw where it would otherwise be detrimental.
3. How are threads made? Explain difference between male and female.
In screw cutting on the geared lathe, the pitch of the thread is determined by that of the lead screw of the lathe itself which traverses the cutting tool across the work. A single point tool is used and several cuts are made to finish the thread. To cut screws of different pitches, the speed at which the lead screw is driven with relation to the spindle is varied by inserting change gears of different diameters in the driving train. The process is a slow one and slight inaccuracies in the lathe itself often make it difficult to make each succeeding cut coincide exactly with its predecessor. In the building and construction threads, anything that sticks out is male and anything that goes in is female, especially if two things fit together whereby one has features that stick out and the other has features that go in.
