Page 361 - Carbide drills I Thread cutting tools 2023

Technical notes regarding use of thread cutting tools

Hardness increase during drilling
For drilling, care has to be taken to ensure that a sharp, intact drill is used. If the wear is already too great,
there is a risk that hardening of the periphery will occur during drilling. One result of this hardening may
be the tap breaking.

Age or precipitation hardening and upsetting the countersink
When preparing for tapping, quality tools should be used which are adapted to the material. If the
counterbore is too worn, the countersink will harden or be upset. This means the tap will encounter
problems as soon as it starts to cut. This can lead to breakage right at the beginning. The countersink
is important in guiding the tap.

Deeper threads
For deep threads, tools must be chosen with sufficiently long flutes. There is otherwise a risk of tool
breakage due to chip build-up, because the chips cannot flow out of the hole. With Rigid Tapping, pecking
in several steps can be programmed, in order to shorten the chips. Sufficient cooling is important.

Functional performance of the compensation chuck
A satisfactory compensation function of the chuck must be guaranteed (no jamming). Otherwise, despite
the chuck, the thread may be miscut or pitch errors can arise. The torque level of the compensation chuck
must be selected according to the thread diameter.

Correctly adjusted coolant jet
A specifically aimed coolant jet is important in tapping work. The direction should be from above, in the
direction of the flutes, so that the cooling is also effective at depth. If the coolant jet is not aimed, the
problem of heat development in the drillhole arises, with the risk of cold welding-together of the
material, which in turn may lead to reduced service life and poor chip formation.

Safety clearance
When using Rigid Tapping, a sufficient approach distance must be programmed. If the clearance is too
small, the problem arises of the machine spindle not synchronising with the feed before entering the
drillhole. This results in pitch error of the thread, even with synchronous working.

Suitability of the machine
On a number of machines, there is a possibility that the recommended RPM cannot be applied. In this
case, the RPM of the machine should be programmed accordingly.

Inconstant RPM
Programming too high RPM can lead to problems: if a RPM is selected which cannot be achieved (due
to the inertia of the machine), the result may be premature breakage of the tool or miscutting of the i
thread. If observed closely, it may often be seen that a high RPM does not in fact produce the time saving
which was intended.

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