Thread cutting method and apparatus

A thread cutting cycle generating apparatus comprising:

• a means for calculating a cutting depth for each thread cutting operation from a first cutting depth from the crest of thread for the first thread cutting operation, a first cutting amount at said first cutting depth or a first command from which said first cutting amount is obtained, a second cutting depth from the crest of thread which corresponds to the bottom of thread, a second cutting amount at said second cutting depth or a second command from which said second cutting amount is obtained, and the equation which expresses the relationship between a third cutting depth from the crest of thread and a cutting amount at said third cutting depth, said first cutting depth and said second cutting depth being commanded for generating a thread cutting cycle in accordance with a thread cutting method in which a thread having a desired shape is obtained by repeatedly conducting thread cutting operations while changing a cutting depth from the crest of thread for the respective thread cutting operations so as to be less than and closest to a predetermined allowable cutting amount;
• wherein the cutting depths for the thread cutting operations from the second thread cutting operation to the thread cutting operation to the cutting depth which corresponds to the bottom of thread are determined in sequence in accordance with a predetermined cutting depth for the first thread cutting operation and a cutting amount at that cutting depth, and a predetermined cutting depth at the bottom of thread and the cutting amount at that cutting depth, and the equation S=axd+b which expresses the relationship between the cutting depth from the crest of thread and the cutting amount, and in that the thread cutting operations are repeatedly conducted using the cutting depths including that for the first thread cutting operation, d being the cutting depth from the crest of thread and S being the cutting amount and a and b being constants.

A thread cutting cycle generating apparatus comprising:

• a means for calculating a cutting depth for each thread cutting operation from a first cutting depth from the crest of thread for the first thread cutting operation, a first cutting amount at said first cutting depth or a first command from which said first cutting amount is obtained, a second cutting depth from the crest of thread which corresponds to the bottom of thread, a second cutting amount at said second cutting depth or a second command from which said second cutting amount is obtained, and the equation which expresses the relationship between a third cutting depth from the crest of thread and a cutting amount at said third cutting depth, said first cutting depth and said second cutting depth being commanded for generating a thread cutting cycle in accordance with a thread cutting method in which a thread having a desired shape is obtained by repeatedly conducting thread cutting operations while changing a cutting depth from the crest of thread for the respective thread cutting operations so as to be less than and closest to a predetermined allowable cutting amount;
• wherein the cutting depths for the thread cutting operations from the second thread cutting operation to the thread cutting operation at the cutting depth which corresponds to the bottom of thread are determined in sequence in accordance with a predetermined cutting depth for the first thread cutting operation and a cutting amount at that cutting depth, and a predetermined cutting depth at the bottom of thread and the cutting amount at that cutting depth, and the equation S=axd.sup.2 +b which expresses the relationship between the cutting depth from the crest of thread and the cutting amount, and in that the thread cutting operations are repeatedly conducted using the cutting depths including that for the first thread cutting operation, d being the cutting depth from the crest of thread and S being the cutting amount and a and b being constants.