I have never completely understood how to do the calculations before beginning to 60 degree single point thread on the lathe, as an example, trying to achieve a correct external and internal 2A & 2B thread that will not only mate with each other but will have a high probability of mating with the opposite gender of any other correctly made thread of the same size, TPI and class. In addition, I have never understood how to correctly calculate the external and internal thread depths when using different profile tools each designed to cut the same TPI. Also, how much, before beginning to cut the threads, to correctly alter the workpieces major and minor diameters between the maximums and minimums for both external and internal threads as shown in the MH book for different diameter and class of threads. Please answer questions 1,2 & 3 below in as much detail as possible, perhaps using a 1”- 8 (2A) and (2B) threads in 1-3/4” 304 round stock for examples. The compound set at 29.5 degrees.
(1) Carbide: The industry seems to offer carbide sharp V point (no flat) inserts for external and internal threading which will cut a range of TPI. They also offer full profile inserts, which are TPI specific. If one were to use the sharp “V” (no flat) insert to cut both the external & internal thread to 100% of the recommended full thread depth, would the two join together (2A and 2B) as smoothly and be as strong as if one used a full profile insert? Probably not, would one then only need to reduce the percentage to get the desired result? If so, what might that percentage be and how would one calculate the new thread depth for both the external and internal thread based on that new percentage? If not, what would need to be done?
(2) HSS: Training books seem to recommend putting a flat on the point of a HSS 60 degree external and internal threading tool. The width of the flat on the point is to be in relation to the TPI the tool is intended to cut. Does one need to change the recommended depth of thread for both the external and internal thread to allow for that flat width? If so, how would one calculate the new thread depth for each flat width for both the external and internal threads?
(3) Workpiece Major and Minor diameters in MH book: Relating below to 2A and 2B threads, how does one calculate how much to correctly alter the workpieces major and minor diameters before beginning to cut and bore the external and internal diameters and before starting to cut the threads. For each thread diameter and TPI the MH book shows a maximum and minimum diameter for both the major and minor diameters. How does one use this information to know what size to pre-cut and bore the workpieces too before threading. Does one pre-cut and bore the internal and external workpieces to the mean between the maximum and the minimum or by some formula, fixed amount or other?
Please all chime-in, these correct thread questions have vexed me for a long time perhaps to the point I’m seeing things to be more complicated than they are. Let me know, Thanks!
(1) Carbide: The industry seems to offer carbide sharp V point (no flat) inserts for external and internal threading which will cut a range of TPI. They also offer full profile inserts, which are TPI specific. If one were to use the sharp “V” (no flat) insert to cut both the external & internal thread to 100% of the recommended full thread depth, would the two join together (2A and 2B) as smoothly and be as strong as if one used a full profile insert? Probably not, would one then only need to reduce the percentage to get the desired result? If so, what might that percentage be and how would one calculate the new thread depth for both the external and internal thread based on that new percentage? If not, what would need to be done?
(2) HSS: Training books seem to recommend putting a flat on the point of a HSS 60 degree external and internal threading tool. The width of the flat on the point is to be in relation to the TPI the tool is intended to cut. Does one need to change the recommended depth of thread for both the external and internal thread to allow for that flat width? If so, how would one calculate the new thread depth for each flat width for both the external and internal threads?
(3) Workpiece Major and Minor diameters in MH book: Relating below to 2A and 2B threads, how does one calculate how much to correctly alter the workpieces major and minor diameters before beginning to cut and bore the external and internal diameters and before starting to cut the threads. For each thread diameter and TPI the MH book shows a maximum and minimum diameter for both the major and minor diameters. How does one use this information to know what size to pre-cut and bore the workpieces too before threading. Does one pre-cut and bore the internal and external workpieces to the mean between the maximum and the minimum or by some formula, fixed amount or other?
Please all chime-in, these correct thread questions have vexed me for a long time perhaps to the point I’m seeing things to be more complicated than they are. Let me know, Thanks!