The following description is based on the centre lathe supplied by H.M.T. Fig. 13.3 shows the various operating controls provided on the machine tool.
1. Head Stock Casting:
The head stock casting is compact and rigid to carry the spindle assembly. The two ribs, apart from contributing to rigidity, carry the pulley on a sleeve which runs in ball bearings housed in the ribs.
Since the sleeve carrying the pulley is independently mounted concentric with the main spindle but clearing it, the belt tension is not directly transmitted to the main spindle. A counter shaft below the main spindle carries a cam which operates a plunger pump for lubrication.
The main spindle runs on a high precision double row taper roller bearing in the front and a single row taper roller bearing in the rear end. The outer race of the rear bearing is spring loaded to allow for thermal expansion of the main spindle.
The main spindle can be run in 18 different speeds by manipulating the speed selector levers of the speed box and head stock. There are six positions for the speed box lever 4 (Fig. 13.3) and for each of these positions, three different speeds are obtained by radially moving the head stock lever 5 (Fig. 13.3) to the different positions marked white, blue and red.
2. Speed Box Unit:
Both speed box and main motor are mounted on a heavy cast iron base plate, which can be easily assembled into the cabinet leg of the lathe as a single unit and does not offer any difficulty in extracting it out for repair and maintenance work. The first shaft of the speed box is directly coupled to the motor.
The seed box is primarily a speed reduction gear box with hardened and ground gears sliding on three shafts running on heavy duty double row ball bearings. The main motor drives the first shaft at motor speed.
A disc cam, which guides the two levers inside the speed box to shift the sliding gears to positions of six combinations, is rotated by the speed selector lever 4 (Fig. 13.3). Thus the speed pulley gets six different speeds.
ADVERTISEMENTS:
These are transmitted to the head stock pulley by a set of six V- belts. The main spindle can be run at the six head stock pulley speeds as well as each of these speeds reduced in the ratios of 1 : 4 and 1 : 16 by means of a reduction drive in the head stock controlled by the selector lever 5 (Fig. 13.3). Thus the main spindle obtains its 18 different speeds.
3. Pedal Brake:
A brake pedal 3 (Fig. 13.3), running the length between the cabinet and end legs ensures sensitive foot control of the main spindle. The pedal when pressed actuates a limit switch to cut off power supply to the main motor and in addition to this applies the brake band over the brake drum on the motor shaft, thereby bringing the main spindle to a quick stop. This arrangement provides extreme convenience in threading against shoulders.
4. Inching:
The push button control ‘inching’ is provided for easy shifting of gears. The control push button for this is housed on the front side of the head stock.
5. Feed Gear Box:
The gear box is of totally enclosed design. A piston pump located inside the feed box and driven by an eccentric on one of the rotating shafts raises oil to a reservoir at the top. From there, oil flows by gravity on the rotating gears.
ADVERTISEMENTS:
The lead screw is protected by a shear pin and the feed rod is provided with a safety clutch.
6. Feed Selection:
Feed selection is done by the manipulation of feed selector levers 6 to 10 (Fig. 13.3). The lever 9 has two positions ‘Neutral’ and ‘Engaged’. Power feed is obtained only when the lever is in the ‘Engaged’ position.
The lever 6 can be moved to positions A, B, C and D; the lever 7 to positions E and F and lever 8 to positions G, H and J. The knurled knob 10 at the bottom of the feed box has 7 positions.
By engaging the levers in different positions as given in the feed charts (Fig. 13.4 & 13.5), 35 different feeds can be obtained. Please note that for feed selection, the lever 7 must be in position E and lever 8 in position H.
Power feed is controlled by lever 13, (Fig. 13.3). From normal position, this lever is simultaneously pulled and moved up to engaged longitudinal feed. For cross feeds, the lever is to be simultaneously pressed towards the apron and moved down. The direction of movement for both longitudinal and cross feed is controlled by lever 12 (Fig. 13.3).
7. Screw Cutting:
The selection of pitch is done by manipulation of the levers 6 to 10 (Fig. 13.3). The thread chart (Fig. 13.6) shows the corresponding positions of the lever for any particular pitch (metric, inch, module or diameter pitches). For the change gear quadrant one extra change gear with 60 teeth is provided.
The thread chart gives the corresponding pitches obtained by the use of this change gear also. When the lever for coarse pitches is engaged in the ‘coarse pitch’ position, the pitches given in the charts are increased in the ratios 4 :1 and 16 :1 for the second and first position of the head stock speed changing lever respectively.
ADVERTISEMENTS:
To start threading, the lever 14 (Fig. 13.3) is moved down to engage the split nut on the lead screw. An interlocking device is provided to prevent simultaneous engagement of the saddle to lead screw and feed rod.
8. Thread Chasing Dial:
The thread chasing dial is provided for re-aligning the position on the lead screw and thereby the position of the tool in subsequent cuts when the split not is disengaged at the end of the thread and the saddle is brought back for re-engagement of the split nut.
While using the machine fitted with the metric lead screw, the thread pitches 0.5, 0.75, 1.0, 1.5, 2.0, 3.0 and 6.0 can be cut without the help of chasing dial since the split nut can be engaged in any position of the lead screw. For cutting other threads the suitable driving pinion A and chaser dial B (Fig. 13.7) is to be selected from the chart (Fig. 13.9) and fitted to the chasing dial unit.
This chart shows:
(i) The number of teeth of the driving pinion A (engaged with the lead screw) to be fitted on the base of the unit.
(ii) The number of guiding lines on the corresponding disc B which is to be fitted on the top of the unit, for each thread pitches. To start screw cutting, the position of the saddle is determined by the coincidence of one of the guiding lines on the disc and the fixed guiding mark when the split nut is engaged.
After the first cut, the split nut is disengaged from the lead screw and the saddle is traversed towards the starting point by means of the hand wheel. For the subsequent cuts the split nut is engaged exactly when one of the guiding lines on the dial coincides with the fixed line.
Metric threads with the inch lead screw can be cut within acceptable tolerance without disengaging the split nut but reversing the traverse of the saddle by using the motor reversing switch in the apron, thus eliminating the use of the screw cutting indicator.
9. Micrometer and Screw Cutting Stop (Refer Fig. 13.8):
The cross slide movement incorporates a micrometer dead stop that can be set in either direction and it can be adjusted with a dial, calibrated to a least count 0.005 mm. A worm on which this dial is fixed is engaged to mesh with a worm wheel on the cross feed screw, by means of a lever provided for the purpose.
A few turns of the hand wheel in either direction brings the cross feed screw in engagement with the worm wheel and stops dead. Now the worm drive provides the micrometer setting. This device is useful in turning and boring in Tool Room as the turning diameter can be set and corrected in steps of 0.01 mm in diameter. Precision depth setting for thread cutting can also be achieved by means of this.
10. Quick Change Tool Post (Refer Fig. 13.9):
The quick change tool post is mounted on the top slide and holders can be clamped within seconds by turning the level A which works on eccentric locking device giving high rigidity to the tool holder. This kind of tool post and present tool holder arrangement eliminates loss of the time.
The tool holder admits a maximum shank size of 25 mm x 95 mm and the tools are rigidly clamped in the tool holder by means of 4 square head screws.
The tool height can be adjusted as follows:
Slide in the tool holder on the tool post, loosen the square head screw C which locks the knurled nut D in the tool holders. Now by adjusting the knurled nut, the tool holder can be raised or lowered. Then clamp the tool holder by turning the lever A and check whether the tool has been centered. If not, unclamp the tool holder and adjust the knurled nut D again. After centering tool, the square head screw C is to be tightened over the knurled nut.
11. Tailstock:
The tailstock is of sturdy design and can be firmly clamped to the bed by means of two easily accessible hexagonal nuts. The taper bore in the spindle is Morse 5. The spindle moves forward when the hand wheel is rotated in the anticlockwise direction. The linear movement of the spindle is read on the graduated sleeve on the hand wheel.
The spindle is clamped by operating the clamping lever. To knock out the drills or centres from the taper bore, the spindle is taken backwards so that the screw rod pushes out them. For taper turning between centres, the tailstock body can be displaced laterally by means of the screw provided on other side of the tailstock.
12. Taper Turning Attachment (Refer Fig. 13.10):
The taper turning attachment to the machine is supplied as a special accessory. For taper turning the two nuts N are loosened, the guide A is adjusted to the required angle and clamped by tightening the nuts N. The nut D is tightened.
The two socket head cap screws E are removed and the screw F is loosened till the cross slide is free of cross feed screw connection. The swivel should be turned 90° and clamped. Now the unit is ready for taper turning. The depth of cut is given through the top slide.
For normal turning operation, the nut D is loosened and the cross feed nut should be brought against the holes for cap screws E. The cross slide is locked with the nut by screwing in the two socket head cap screws and tightening the screw F.
