1. 4.4 Size of a Horizontal Boring Machine:  Conventionally, the size of a horizontal boring machine is specified by the spindle diameter in mm.  The spindle diameter varies from 75 to 355 mm. To completely specify a boring machine following important dimension must be mentioned. i.Spindle motor horse power. ii.Column height. iii.Size of the table or size of the floor plate. iv. Spindle size, number of feeds and length of feeds. v. Weight of the machine. vi. Floor space required. HCET1

2. 4.4.1. Boring Machine Mechanism: The machine contains different controls for movement of the different parts of the machine.  A table type machine has the following movements: 1. Headstock and end supporting block- vertically up and down. 2. The spindle rotational motion and longitudinal movement. 3. The saddle and the table- linear movement by hand or power. 4.The columns may be moved by hand or power.  All these movements may be given independently or in combination with two or more movements.  As all the controls are housed in a particular position of the machine the operator may give a closer attention to the work while controlling the machine. HCET2

3. 4.4.2. Work Holding Devices for Horizontal Boring:  The work may be supported on the table by the conventional work holding devices or by special fixtures.  Conventional work holding devices comprise T-bolts and clamps, angle plate, step blocks, etc.  Special jigs are used in mass production work. The jig locates the work as well as supports and guides the boring bar. 4.4.3. Horizontal Boring Machine Operations:  In boring operations, the work remains stationary and the tool is given the rotary motion.  Holes are bored by using boring bars; multiple holes may be bored one after another by changing the position of the work piece and aligning it each time with the boring bar.  The boring bar is fitted to the spindle and cutter is adjusted in the boring bar to the required dimension and a light cut is then taken.  Figure shows a boring machine. HCET3

4.  To perform milling operation on a boring machine, any type of milling cutter may be fitted to the spindle.  Facing cutter is used for produce flat vertical surfaces, operation known as facing. For this operation, the tool or work may be fed to complete the cut. End mills are used to produce grooves and slots.  Face milling operation is shown in figure. HCET4

5. 4.4.4. Boring Tools Mountings for Horizontal Boring:  Various mounting equipments/tools used for cutters in a horizontal boring machine are: 1. Boring bar 2. Boring head or cutter head 3. Facing head. 4.4.4.1. Boring Bar:  Ordinary boring operations are carried out with tools mounted on a bar held in spindle having Morse taper hole.  The maximum diameter of the bar is normally not larger than the spindle diameter, and the length is sufficient to reach the end column support.  To reduce bending or vibration, a boring bar should be of maximum diameter and minimum length and it may be supported in various ways to match with different types of work pieces. HCET5

6.  Methods of supporting boring bars are explained below:  Supported by spindle: For boring blind holes, bars are supported at the spindle end only. This type of bar is called a slub bar.  Supported by spindle and end column: For boring long open holes, boring bars are supported at the end and by a bearing block mounted on the end supported column at the other end.  Supported by the work piece: In some of the works, the bar may be supported in the bored holes of the work by bushings. This type of support takes longer setting time, and is used in stray jobs having very small lot size that do not justify cost of a special jig. Figure shows a boring bar supported by the bushings in the work piece. HCET6

7.  Supported by boring fixtures: In mass production work boring jigs are used to locate, guide and support bars at intermediate points as shown in figure.  Boring bars used for boring smaller diameter holes are made of manganese-chrome alloy steel annealed to relieve internal stress.  Heat treated bars of medium carbon steel alloyed with chromium and manganese are used where serves cutting condition exists. HCET7

8. 4.4.4.2. Methods of attaching cutters on boring bars:  Cutters can be attached to baring bars by various methods. Slots are cut at intervals along the entire length of the bar so that cutter may be set at the required position.  Different types of cutters are used for different classes of work. The most important type of cutter is a fly cutter. It consists of a single point cutting tool mounted on a bar. Figure 4.11 shows Fly cutter.  In production boring double cutters are widely used as it reduces the operation time to a great extent. Fig 4.12 shows a double cutter. HCET8

9. 4.4.4.3. Boring head or cutter head:  For machining large diameter holds, the boring are used for mounting cutters, where a standard boring bar is not suitable because of smaller or excessive overhang of the cutter.  Boring heads having maximum permissible are either bolted or keyed on the spindle, which hold two or more cutters.  This device supports the tool sufficiently and reduces machining time due to having larger number of cutting edges.  Figure 4.13 shoes a boring head. The cutter may be adjusted by micrometer dials. HCET9

10. 4.4.4.4. Facing Head:  The facing heads are mounted at the end of the spindle. It comprises a flange provided with a diametric slide-way on which the tool carrying a bracket may be adjusted.  The bracket may be fed radially or located and clamped at the centre to support a long boring bar.  The facing head allows enlargement of large diameter holes, facing and external turning operations. Figure 4.14 shows a facing head. HCET10