Every kind of mechanical instrument has screws and nuts to hold the various parts of the machine in place. It could be an instrument as simple as the normal door hinges or the most sophisticated instruments like aircraft doors. The screws have tremendous use in attaching the doors to the aircraft. Hence, they require the screws of high durability and strength. The lead screws that the industry uses have either ACME threads or trapezoidal threads. Hence, you need ACME thread gauges
or the trapezoidal thread gauges.
There is not much difference between the ACME threads and the trapezoidal threads. The difference is just one degree. The ACME threads have grooves at an angle of 29 degrees whereas the trapezoidal threads have them at 30 degrees. However, this one degree matters a lot because you will not be able to use the same gauge to measure the pitch and tolerance levels. You need special ACME thread gauges and trapezoidal thread gauges.
Let us look at the characteristics of the ACME threads.
The major characteristic of the ACME thread is the 29 degree thread angle with a thread height half of the pitch. The apex and the valley of the thread are flat. Hence, this shape is easier to machine as compared to the square thread. As the tooth shape has a wider base, these screws are capable of carrying greater loads. They are infinitely stronger than the normal threads or the screws with square threads. This form also allows the use of the split nut thereby compensating for nut wear.
The disadvantages of the ACME thread are that there can be a higher degree of friction thereby reducing its efficiency. There are also chances of shift of the radian load on the nut. In spite of these drawbacks, the ACME thread has its utility value. They perform great as lead screws, especially in testing machines, jacks, aircraft flaps and conveyors. The industry makes use of the long-length ACME threads for these purposes. Similarly, the short-length ACME threads have use on valve stems, hose connectors, steering mechanisms, and camera lens movement.
The trapezoidal threads differ from the ACME threads in the sense that the threads have an angle of 30 degrees instead of 29. You can find the use for the trapezoidal thread in lead screws like that on the lathe. There are standard variations of the trapezoidal threads like the multiple-start threads, left-hand threads, and self-centering threads. The advantage of the self-centering threads is that they are less likely to bind under lateral forces.
The trapezoidal thread is a universally recognized thread form. These threads have use in virtually all kind of industries purely because they are powerful in their individual way and are capable of carrying heavy loads.
Measuring the tolerance of these threads is important. You need special thread gauges like the ACME thread gauge to measure the pitch of the ACME threads. Just like all kind of gauges, this gauge has a Go as well as NO Go side. The same principle applies as far the importance of these sides is concerned.