Group No: G7

Module Name: ME1071

Semester: 2

BASIC MACHINING OPERATIONS

USING METAL LATHE

By

Index No. Name Marks

200275A JEYARAJ J.S.P.

Date of practical session

Date of submission

Instructor’s name

Department of Mechanical Engineering

University of Moratuwa
Sri Lanka
INTRODUCTION

Machining is the process of removing material from a workpiece to get it into a desired shape and size
to get useful work out of it. The key principle behind machining is the removal of material by rubbing
a cutting tool on a workpiece so that the unwanted parts are removed from the workpiece. For this the
appropriate cutting tool and the appropriate operation should be chosen. Lathe machines are widely used
in machine shops for machining operations. Lathe machines can perform the following operations and
more.

 Turning: This is done when the diameter of a workpiece

 Grooving: This is done when the diameter of a mid-section of the workpiece must be reduced
 Facing: This can be done to reduce the length of workpiece or to flatten the surface of a
workpiece
 Thread cutting: To cut external threads
 Drilling: Making drill holes in a workpiece

These are just a few operations performed by the lathe machine. Usually, the workpiece is rotated while
the cutting tool is advanced or moved out of the workpiece. Apart from the lathe machine, work holding
devices such as chucks and clamps and tightening tools such as keys and wrenches and measuring tools
are used in the machine shop.
 STEPS FOLLOWED IN PRODUCING THE SHAFT

TOOLS AND MACHINES USED

 Lathe machine
 Centre
 3 jaw chuck
 Drill bit
 Turning tool
 U’ cut
 Lathe dog
 Micrometer screwgauge
 Oddleg calliper
 Steel ruler


PROCEDURE

I was given a mild steel workpiece cut out of a long cylindrical mild steel rod. The faces were not flat
in this workpiece. I first adjusted the tool to the centre of the machine using the centre. After adjusting
the tool to the centre, I attached the workpiece to the 3-jaw chuck. Then I tightened the chuck using
chuck key and removed the chuck key and place it in the toolbox. Then I brought the adjusted facing
tool close to the face of the workpiece, then I advanced the tool about 1mm into the workpiece and
switched on the lathe machine. Then I switched on the auto forward actuating switch and let the
workpiece to get faced automatically.

After the facing was done, I removed the centre from the tailstock and placed the drill bit holder properly
such that it locks itself in place. Then I advanced the tailstock towards the workpiece and switched on
the lathe machine then while cleaning the drill bit with a brush I slowly advanced the drill bit into
smoothed face of the workpiece. This whole was made such that the workpiece could be held with 2
centres in the next steps. This flattening process and the drilling are repeated on the other side too.

Figure 1 Figure 2
Then I attached another centre on the 3-jaw chuck and another on the tailstock. Then I fixed the
workpiece tightly between the two centres (the workpiece is mounted on a lathe dog before this). Then
I switched on the lathe machine marked 140 mm from the face on the workpiece. This was marked by
just touching the workpiece with the turning tool (now fixed to the tool post). Then I took the turning
tool to the end of the shaft and just touched the shaft with it. Then I took it out of the workpiece area
and measured the diameter of the rod. Since it was greater than 23mm I reduced the diameter of the rod
until the 140mm mark. Once the diameter was close to 24mm I started to reduce the diameter of the rod
by advancing the tool using the fine adjustment knob. The motion of the tool over the marked area was
done using the automatic motion switch.

Figure 4

After the diameter was reduced to 23mm throughout the 140mm distance using the same method I
marked 20mm in front and reduced the diameter to 16 mm in that 20mm section.

Then I turned the tool post to the 90⁰ and adjusted the tool and then I turned the tool post to 100⁰ mark
and cut the taper of 16mm to 20mm. This option doesn’t have automated actuation, so I had to move it
forward manually.

Figure 5

Once the taper was cut, I changed the tool to a u’ cut tool and made a groove in the workpiece. This
groove is useful in the thread cutting step and prevent threading tool from breaking by hitting the taper.

Then I adjusted the settings of the lathe machine to the threading setting to get a 2mm pitched buttress
thread. Then using the fine adjustment screw I advance the cutting tool stepwise 0.2, 0.6, 1.0, 1.4, 1.8,
2.0, 2.2, 2.4 mm to cut a thread which is 2.6mm. On the 2.4mm setting I sent the tool twice to get the a
smoother finish. It is better to cut threads in the fastest thread cutting speed possible but we were advised
to use a moderate speed because we are still inexperienced. Frequent lubrication was done when cutting
the thread to reduce friction.
 Figure 6

Some tools used are highlighted

 SAFETY PRECAUTIONS

GENERAL SAFETY PRECAUTIONS FOLLOWED IN THE MACHINE SHOP

No loose/hanging clothes were allowed in the fitting shop as they can get entangled in moving parts of
machines and cause damage to us and machines.

Safety shoes were recommended however if they are not available hard leather shoes are manageable.
The shoes are compulsory to protect the feet from heavy items which may fall onto them causing
damage.

Wearing gloves is compulsory as injuries to hands may occur from hot metal chips, heated workpieces
or tools.

Goggles must be worn when using lathe machines as hot metal chips might get thrown into the eye from
the workpieces.

When moving around marked walking path must be used and after using one item it should be replaced
in the proper location, so that it will not get lost, or it will not cause harm to another.

Others must not be disturbed; therefore, loud noises and unwanted distractions must be avoided.

IMPORTANCE OF CUTTING FLUIDS

Due to the friction between the rotating workpiece and the cutting tool, the workpiece or cutting tool
tends to break off. A very high heat is also produced due to this friction making the cut off metal pieces
very hot and dangerous to the user. To prevent these unfavourable effects, we use lubricants to reduce
the friction and to cool down the workpieces and tools. Usually, coconut oil is used for this purpose but
for high speed and heavy cuttings there are specialized lubricants.

CUTTING TOOL MATERIALS

 Carbon Steels: Steels of C percentage about 1 – 1.2% are usually used for cutting purposes.
These are quite inexpensive but at temperature above 205 ⁰C these loose their cutting ability,
hence frequent lubrication needs to be done.
 High speed steel: These can operate at speeds twice or thrice that of carbon steels. This usually
contains 18 percent tungsten, 4 percent chromium, 1 percent vanadium, and only 0.5 to 0.8
percent carbon. This has made lathe operations much faster and efficient.
 Cemented Tungsten Carbide: These are made by binding finely divided tungsten carbide by a
binder of cobalt. These are very close to diamonds in hardness, hence can operate at very high
speeds than high speed steels.
 Cast alloys: These can cut effectively even in very high temperatures. These are mostly used to
cut cast iron components effectively. Usually cobalt, chromium and tungsten are used to make
these alloys.
3-JAW CHUCKS AND 4-JAW CHUCKS

Both the 3-jaw chucks and 4-jaw chucks are used as work holding tools. The main difference is that the
3-jaw chuck has 3 jaws and 4-jaw chuck has 4 jaws. With the increase ofnumber of jaws the gripping
force of the chucks increases hence the 4-jaw chuck can grip better than the 3-jaw chuck.

A 3-jaw chuck can only hold hexagonal and circular shapes but on a 4-jaw chuck circular, square,
rectangular, and octagonal shapes can be attached. Hence, the chuck should be chosen according to the
shape of workpiece. Most of the 3-jaw chucks are self-centering hence easier to mount things on it,
while most 4-jaw chucks must be adjusted manually hence making the operation harder but these are
more accurate than self-centering chucks.

Figure 7
 STEPS FOLLOWED IN PRODUCING THE SHAFT

TOOLS AND MACHINES USED

 Lathe machine
 Centre
 3 jaw chuck
 Drill bit
 Turning tool
 U’ cut
 Lathe dog
 Micrometer screwgauge
 Oddleg calliper
 Steel ruler

PROCEDURE

The given workpiece is 100mm long and 50mm of diameter. The faces might not be flat in this
workpiece. I will first adjust the facing tool to the centre of the machine using the centre. After adjusting
the tool to the centre, I will attach the workpiece to the 3-jaw chuck. Then after tightening the chuck
using chuck key, I will bring the adjusted facing tool close to the face of the workpiece, then I will
advance the tool about 1mm into the workpiece and switch on the lathe machine. Then I will switch on
the auto forward actuating switch and let the workpiece to get faced automatically.

After the facing is done, I will remove the centre from the tailstock and place the drill bit holder properly
such that it locks itself in place. Then I will advance the tailstock towards the workpiece and switch on
the lathe machine then while cleaning the drill bit with a brush I will slowly advance the drill bit into
smoothed face of the workpiece. This hole is made such that the workpiece could be held with 2 centres
in the next steps. This flattening process and the drilling are repeated on the other side too.

Then I will attach another centre on the 3-jaw chuck and another on the tailstock. Then I will fix the
workpiece mounted on a lathe dog tightly between the two centres. Then I will switch on the lathe
machine and mark 75 mm from the end of the workpiece. This is marked by just touching the workpiece
with the turning tool (now fixed to the tool post). Then I will take the turning tool to the end of the shaft
and just touch the shaft with it. Then I will take it out of the workpiece area and measured the diameter
of the rod. Since it will be closer to 50mm I will reduce the diameter of the workpiece from the open
end to line 1-1 to 20mm, line 2-2 to 3-3 to 40mm, line 4-4 to 5-5 to 20mm.

Then I will turn the tool post to the 90⁰ and adjust the tool and then I will turn the tool post to 135⁰ mark
and cut the taper of 20mm to 40mm within 10mm. This option doesn’t have automated actuation, so it
must be moved forward manually.
Once the taper is cut, I will chamfer the end of the workpiece just touching the workpiece with the
turning tool at an angle. I will then change the tool to a u’ cut tool and make a groove in the workpiece.
This groove is useful in the thread cutting step and prevent threading tool from breaking by hitting the
taper.

Then I will change the tool to thread cutting tool to and will adjust the settings of the lathe machine to
the threading setting to get a 2.5mm pitched buttress thread. Then using the fine adjustment screw I will
advance the cutting tool stepwise 0.2, 0.6, 1.0, 1.4, 1.8, 2.2, 2.6, 2.8 mm to cut a thread with depth 3mm.
On the 2.8mm setting I will send the tool twice to get a smoother finish. Then I will clamp the threaded
end to the 3-jaw chuck and cut off the part out of the 1-1 line using parting off tool.

Figure 8

Figure 9
REFERENCES

 J. Sabhadiya, “Different types of threads and their uses,” Engineering Choice, 05-Jul-2022.
[Online]. Available: https://www.engineeringchoice.com/types-of-threads/. [Accessed: 29-Sep-
2022]
 “Tool materials,” Encyclopædia Britannica. [Online]. Available:
https://www.britannica.com/technology/machine-tool/Tool-materials. [Accessed: 29-Sep-
2022]
 “Thread geometry - metric coarse,” TR knowledge base | Thread geometry - metric coarse.
[Online]. Available: https://www.trfastenings.com/knowledge-base/thread-geometries/metric-
coarse-standard. [Accessed: 29-Sep-2022]
 written by John, “3 jaw Chuck vs 4 jaw Chuck: Differences explained,” MellowPine, 04-Sep-
2022. [Online]. Available: https://mellowpine.com/blog/3-jaw-chuck-vs-4-jaw-chuck/.
[Accessed: 29-Sep-2022]