IX. Describe Fig. 22 orally using the following words and word combinations:
the body of a twist drill, to represent, a cylindrical rod, to have two spiral grooves, to serve, forming, the cutting edges of the drill, to be called lips, the lips, to be connected, a third edge, to be known, a web, to penetrate into material by rubbing, the shank, the drill, clamping the drill in the chuck, to be of different shapes, cylindrical shanks and tapered shanks, the third part of the drill, a drill point, to be ground to a cutting angle, to depend on, material to be drilled
8. Threading tools
There are different types of thread-cutting tools depending upon the operations to be performed. Thread-cutting tools are classified according to the work done into female screw-cutting tools and male screw-cutting tools.
According to their construction they are known as taps, nut taps (Fig. 23), and threading dies. The tap used for cutting female threads in holes is made in the form of a screw provided mostly with straight grooves forming the cutting edges of the tool. The tap made of a steel cylindrical bar stock consists of the working part and the shank.
Fig.
23.
Set of Taps
The shank serves for fastening the tap in a chuck or in a tap wrench (Fig. 24).
Fig.
24. Tap Wrench
Threads can be cut by means of taps either by hand or on a machine. With manual tapping usually a set of two or three taps is used. The first tap serves for cutting threads; then the second tap is used; the third tap is applied for final thread cutting. With mechanical tapping in such materials as cast iron, bronze, brass, copper, aluminium, etc. one tap is used. When steel is tapped sometimes a set of two tools is used. Before cutting threads the tap should be set so that its axis strictly coincides with that of the hole to be cut, otherwise the thread may be oblique. To cut male threads such an instrument as a threading die is used, which is held in the die holder (Fig. 25).
A threading die is usually made of internally threaded flat steel stock with cutting grooves or flutes. Between these grooves or flutes there are the cutting edges of the tool by means of which male threading is performed.
Threading Die Die Holder
Fig. 25.
Exercises
I. Translate the following words and phrases from the text:
thread, to classify, female screw-cutting tools, nut tap, to tap, threading die, die holder, tap wrench, male threads, female threads
II. Retell the text giving answers to the following questions:
1. How are thread-cutting tools classified according to the work done by them? 2. How are thread-cutting tools classified according to their construction? 3. What instrument is used for cutting threads? 4. What is the construction of a tap? 5. How can threads be cut? 6. What is needed for manual tapping? 7. What is the purpose of the first, second and third tap? 8. How should the tap be set before cutting threads and why is it necessary to do that? 9. What instrument is used for cutting male threads?