Quite often, in practice, one has to face the need to cut the threads of the desired diameter in any hole. With the apparent simplicity of this process, some specific rules and sequence of actions must be observed.
1
It should be remembered that the passage hole for cutting the thread should be a slightly smaller diameter than the diameter of the thread itself. There are special tables containing the dependence of the diameters of the hole and threads. For example, for the M3 thread, a passage hole with a diameter of 2.5 mm is necessary, and for thread M5 - 4.2 m. If the hole is larger, then the thread will turn out to be “glued” and the fasteners will not be durable. If the diameter of the hole is smaller than the tabular, then a greater force will come to the tap and there is a risk of breakdown. It should also be remembered that to form a thread in deaf holes, it is necessary to drill it to a greater depth than the estimated thread length. The shape of the tap makes it impossible to cut the thread to the full depth of the hole.
2
Cutting threads is carried out in several passes, usually in three. Taps are divided into draft, medium and finishing. You should start cutting the thread with a black tap, then the passage is made by medium and ends in finishing. If you make a thread with any one tap, then the thread will turn out to be rough and there is a risk of damage to the tool in the hole. It should be remembered that after one full turn of the tap, it is necessary to make half the turn in the opposite direction. This facilitates the separation of the chips from the surface of the passage hole and promotes its exit from the thread. And always use a working, not worn tool. Then the probability of sending an important part to marriage is sharply reduced.
3
In the process of cutting, it is necessary to use lubricating materials. Usually these are turpentine, kerosene, linseed and spindle oil. Do not use motor car oils, as this helps to stick the chips onto the tap and clogging the thread grooves. To cut the threads in stainless steel, ordinary lard is used. The process of cutting in bronze or cast iron details does not require additional lubrication.
4
After cutting, it is necessary to clean the hole from the chips and the remains of the metal to the maximum - blow out with compressed air, rinse with kerosene or solvent. Special “ruffs” for cleaning threaded holes perfectly perform their function.
5
Well, the most important thing is skill and experience. This comes only with practice. Therefore, we train, break taps and train again. Very soon, the thread cutting process will cease to deliver any troubles to you.
That's basically it. We hope that these brief recommendations will very soon allow you to feel like a real professional.
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