Machine Tools Classification

 

At the present time the machine-tool industry produces a large number of metal-cutting machine-tools different in purpose, processing capacities, degree of automatization and size. According to domestic classification, all machine tools are divided into ten main groups depending upon the type of processing operation they perform or tools they employ:

0-reserve group; 1-lathes; 2-drilling and boring machines; 3-grinding and microfinishing machines; 4-combination machine tools; 5-gear-and-thread-cutting machines; 6-milling machines; 7-planers, shapers, slotters and broaching machines; 8-cutting-off machines; 9-miscellaneous.

Each main group, in turn, is further divided into ten subgroups. For example, for lathes we have: 0-special, 1-automatic and semiautomatic single-spindle, 2-automatic and semiautomatic multiple-spindle, 3-turret lathes and so on.

Each subgroup is subdivided into some type, size and modification classes, or sub-subgroups. For example, 1K62 is specified:

1-machine tool of lathe group engine turning, threadcutting and facing lathe;

6-engine and facing lathe (subgroup);

2-maximum radius of work is 200 mm (size class);

K-modification.

But, basic model of the 1K62 engine lathe has the following modifications: model IK62A with tracer control, model 1K62B, which is the same model but of higher accuracy, model 1K62T, which is a high-precision lathe, model lK62ПУ with numeral controls and so on.

 

Lathe Works

 

The lathe is a machine tool that holds work between centers or in a chuck while it is rotated against a fixed tool to form a surface of revolution, e.g. cylindrical, conical and contoured surfaces.

Besides the basic operations of turning, facing, boring, drilling, threading, etc., the lathe can also do milling, shaping, gear cutting, fluting and grinding. Any other machine tool cannot perform such a variety of operations. For continuous or heavy-duty work a specialized machine tool is recommended for these secondary operations.

The Fig. 6.4 represents the simplified scheme of the model 1K62. The principal parts of the lathe machine 1K62 are: bed with two legs 1 and 15, headstock 2, tailstock 14, carriage 7 and chuck 6 on spindel. The speed gearbox 5 is driven through V-belts from electrical motor housed in the left leg 1 of the bed.

Fig. 6.4. Engine lathe: 1, 15 – legs; 2 – headstock; 3 – teed gear box; 4 – V-belts transmission;

5 – speed gear box; 6 – chuck; 7 – carriage; 8 – sledge; 9 – turning tool-holder;

10 – support; 11 – apron; 12, 13 – screws; 14 – tailstock

 

Thanks to combination of 26 gears the spindel and chuck 6 with a workpiece have variable rotation speed.

Before starting any work the work piece must be clamped with a chuck 6, when it has small length, or with the chuck and center of tailstock 14, when it is long enough (l>3d). The tool-holder 9 is mounted on support 10, which may perform 4 motions (Fig. 6.4 and 6.5):

- longitudinal S_L together with carriage 7 along slide bars;

- crossing one S_S;

- revolving one S_r;

- inclined to spindel axis S inc (Fig. 6.5k).

The tailstock moves manually on slide bars and its center has longitudinal motion by manual wheel. Instead of center the drill or the reamer may be installed.

In the headstock the feed gear box 3 is placed. It revolves screw 13, which moves carriage and special chisel when thread is cut. Longitudinal and crossing motions of support 10 with chisel may be carried out manually by wheels or by power drive and screw 12.

Figure 6.5 shows workpieces upon which numerous operations have been done. A study of this illustration will give some indications as to why different tools are used for turning (a), facing (b), necking and parting (c), drilling (d), boring (e), threading (f), forming (g), tapering (h, k).

Fig. 6.5. Cutting operation used in lathe work: a – turning; b – facing; c – necking or parting;

d – drilling; e – boring; f – threading; g – forming; h, k – tapering

 

Tools are classified according to their designated purpose (operations), location of the main cutting edge (right - hand and left-hand), shape and material of the blade, etc.

A lathe can be used for drilling and boring. The process is called drilling, when a hole is to be cut in a solid work piece. In the lathe the drill is inserted into the tailstock sleeve.

Drilled holes or integrally cast holes of castings are frequently bored to the finished size (Fig. 6.6).

Fig. 6.6. Cutting inside contours: a – a face; b – a conic surface

 

Drilling

 

6.7.1. Main Operations

 

There are several operations of holes machining that are usually done by a drilling machine.

Drilling is an operation of producing a circular hole by removing solid metal. The cutting tool used is called a drill. The drills are most commonly used in the machine shop are twist drills.
Figure 6.7 shows such a drill with the main parts identified.

The drill has two (main) cutting edges and one crossing cutting edge. The dimensional accuracy of drilling (Fig. 6.8a) is not high.

Boring is the operation of enlarging a hole with a drill (Fig. 6.8b), or by means of a cutting tool with 3 and more cutting edges, named a bore (Fig. 6.8c), or by means of an adjustable cutting tool with only one cutting edge (Fig. 6.8d, e). The bore is similar to the drill, but without crossing cutting edge.

Reaming (Fig. 6.8 f) is an operation of sizing and finishing a hole by means of a cutting tool having several cutting edges. This tool is called a reamer. Reaming serves to make the hole smoother, straighter and more accurate.

Boring provides higher shape and dimensional accuracy than drilling.

Counterboring (Fig. 6.8 g) is an operation of enlarging the end of a hole cylindrically, as to produce recess for a fillister-head screw.

Countersinking (Fig. 6.8 h) is an operation of making of coneshaped enlargement on the end of a hole, as to make recess for a flathead screw.

Spot-facing (Fig. 6.8 i) is an operation of smoothing and squaring the surface around a hole, as for the seat for a nut or head of a cap screw.

Some bores have guide cylinder for getting an alignment of a drilled hole and cutting hole or surface.

Fig. 6.7. Parts and elements of twist drill: l₁ - body; l₂ - lip; l₃ - neck; l₄-shank; l₅ - tang;

1-main cutting edge; 2-cross cutting edge; 3-top rake; 4-back rake

 

Fig. 6.8. Main operation of hole machining: a – drilling; b – boring; d, e – enlarging by cutting tools;

f – reaming; g – counterboring; h – countersinking; i, j – spot-facing; k – threading

 

Treading (tapping) (Fig. 6.8 k) is an operation of forming internal threads with a tool called a tap. To withdraw the tap by power in a drilling machine either a reversible motor or reversing attachment, or tapping attachment are required. To withdraw a tap by hand it is necessary to loosen the chuck or other holding device.

6.7.2. Drilling machines

 

Drilling is one of the oldest methods of tooling. Most different materials such as wood, metals, and plastics are drilled by means of appropriately shaped tools.

Drilling machines are primarily used for making and treating the cylindrical holes. Drilling and other operations frequently serve to prepare metal parts for riveting, bolting, pinning and other operations.

In metal working the bench-type (Fig.6.9), upright (Fig.6.10), radial (Fig.6.11) drilling machines, boring and fine boring (Fig. 6.12) machines are used.

The drilling spindle 1 of bench type machine can be moved vertically up and down by manual control 2. The cone pulley 3 of the drilling spindle is connected with a cone pulley 4 of an electric motor 5 by a belt. Normally three-step cone pulleys are used. Thus, a range of three speeds is obtained, which are selected by shifting the belt onto the various steps of the cone pulleys. A tool holding device 6 is fitted on the lower end of the drilling spindle. The column 7 is fitted on the cast-iron bed 8.

 

Fig. 6.9. Bench-type drilling machine: 1 – sprindle; 2 – handle; 3, 4 – cone pulleys of V-belt transmission;

5 – electric motor; 6 – chuck with drill; 7 – column; 8 – bed

Fig. 6.10. Upright drilling machine: 1 bed; 2 – column; 3 – table; 4 – spindle; 5 – feed gear box;

6 – speed gear box; V – spindle (tool) revolution; S_f – feed motion;

S_v – vertical motion of table 3 and feed gear box 5

 

 

Fig. 6.11. Radial drilling machine: 1 – plate; 2 – bed; 3 – rotating (S_r) column;

4 – rotating together with column and moving up and down (S_v) traverse; 5 – moving mechanism;

6 – spindle head, moving horizontally (S_h); 7 – gear box of springle head; 8 – feed mechanism;

 9 – spindle; 10 – table

Fig. 6.12. Fine boring machine: 1-bed; 2-frame; 3-drive; 4-boring head; 5-spindle; 6-table; 7-carriage; 8-drive

 

The design of upright drilling machines (Fig. 6.10) in essence resembles that of a bench type drilling machine. Modern upright drilling machines, however, are not driven by means of a belt drive. The gearcase 6 houses several pairs of gears, which can be engaged by appropriate shifting levers. In this way a wide speed range is ensured (more than 30 speeds).

If material is hard or drills of a large diameter are used, the manual power by means of hand lever will not suffice to perform the feed motion S_f. Therefore, upright drilling machines are equipped with feed-gear mechanism 5 which can be thrown into gear when required. From this follows that there are two possibilities of feeding the drilling spindle 4 (Fig. 6.10). First, the spindle can be fed manually with the feed-gear mechanism disengaged. Secondly, the required feed motion from motor through gearcase 6 and spindle 4 can be effected by means of the feed-gear mechanism 5. The feed-gear mechanism together with spindle, tool and table 3 can move vertically up and down (S_v) along slide bars.

For large workpieces, or workpieces, which require very precise holes, radial drilling machines or jig boring machines are used.

The design of the radial drilling machine (Fig.6.11) in essence resembles that of the upright drilling machine, but its spindle, except vertical S_v, can do two horizontal motions by rotation column 3 S_v and horizontal replacement of spindle head 6 S_h on the traverse 4. The part to be worked up is fixed on the table 10 or on the plate 1.

The fine-boring machine (Fig. 6.12) has spindle 5, which can do two motions: rotating V and vertical S_v ones. The machine has a table, which can do two horizontal motion: S₁ (perpendicular to the drawing plane) and S₂ (parallel to the drawing plane) with very high accuracy (±0.001 mm). The highest accuracy in operation of these machines is achieved by means of

- high accuracy of transference mechanism of table;

- holding constant temperature (20 ± 1 °C);

- sometimes using diamond tools.

Except vertical drilling machines there are horizontal drilling and boring machines of different types.