geneva mechanism

1. Project Submitted by:
Arka Raha 1457017
Arkajyoti Mukherjee 1457011
Ayan Ghosh 1457044
Sundar Bhattacharjee 1457060
Aneesh Ghosh 1457066
Sauradeep Biswas1457076
Pranshu Shubham 1457117
Under the guidance of
Dr. Jyotirmoy Saha
Professor
Mechanical Engineering Department
Heritage Institute of Technology,Kolkata

2. What were the drawbacks of conventional
Centre Lathe?
 The idle time involved in setting and movement if Tool was large
 1 Tool at a time can be used
Thus the Centre Lathe was modified to improve the production rate
in a Mass Production Manufacturing System.
They are 1) Semi Automatic Lathes – Turret Lathe & Capstan Lathe
2) Single Spindle Automats /Automatic Lathes –
a) Swiss Type Automats
b) Turret Type Automatic machine
The Improvements are basically in the following area:
 Multiple Tool Availability
Automatic Feeding of Tools
Automatic Stopping of Tools at precise locations
Automatic Control of the proper sequence of Operations

3. Evolution of Single-spindle
Automatic Lathe
The history of automatic lathes in industrial contexts
began with screw machines during the development arc
of 1760-1840.
In the 1870s, the turret lathe's part-cutting cycle
(sequence of movements) was automated by being put
under cam control. According to Rolt (1965), the first
person to develop such a machine was
Christopher Miner Spencer, a New England inventor.
Charles Vander Woerd may have contemporarily
independently invented a machine similar to Spencer's.

4. •The single spindle automatic lathe is a form of
metalworking lathe that is used for repetitive
production of duplicate parts.
•It consists of an indexable tool-holder that allows
multiple cutting operations to be performed.

5.  Indexing is basically rotating the tool-carrier of the lathe through a
definite angle into a new location or position quickly and precisely.
 Geneva mechanism is a pin and slotted disc mechanism that translates a
continuous rotational movement into intermittent rotary motion.
 It is a simple and inexpensive method of indexing.

6. Working of a Geneva Mechanism
•If the driven wheel has n slots, it advances by 360°/n
per full rotation of the drive wheel
•There are three types of Geneva drives: internal,
external, spherical.

8. Automatic Locking Mechanism
Motivation
•The philosophy is to positively locate and prevent the geneva wheel from
rotating over the major part of rotation of the driving member.
•. It is known to attempt to overcome this difficulty by providing a spring
loaded profiled bolt which co-operates with the geneva wheel in its
ostensibly locked condition.
•In order to obtain satisfactory retention of the driven wheel against
movement during an operation which is being carried out on a work piece
whose relative location is established as aforesaid, it has proved necessary
to provide the bolt with a heavy spring loading.
Mechanism
•The Indexing operation is carried out as the turret slides to the right via
the gear sector and bell crank lever arrangement which moves the rack to
the right aided by a cam mounted on a auxiliary camshaft triggered by a
single revolution clutch and trip dog mounted on the camshaft.

9.  Before starting the rotation, the locking pin is withdrawn by a cam
lever mechanism shown in the diagram below. Before and after
engagement of the driving pin, the locking pin is, respectively,
withdrawn and reset by a lever as shown in the figures below.
 The driving disc with the pin is rotated at preset moment(s) by exact
one revolution which is received from the auxiliary shaft by a single
revolution clutch through the gears

11. Problem Specification
 Till now we have designed the components,assembled it in Creo Parametric
5.0 and conducted kinematic and Acceleration Analysis both mathematically
and through the simulation module.
 The dimensions of each components are taken as standard dimensions as
given by our project guide.
 Since the whole arrangement works within a low limits of acceleration,the
torque generated on critical components will be very much low. Thus we do
not need to do further stress analysis.
Turret size 150 mm (diameter)
Turret slide size 200 mm
Turret holding shaft 25 mm(diameter)
Pin disc size 50 mm radius at pin centre
Pin diameter 8 mm
Single revolution clutch Manually Triggered

12. Objective: To Find the required Diameter of the Geneva Wheel
Here, r=50 mm
The driving or the pin disc rotates at uniform angular velocity, ω ,which is
ω =2πn/60 = πn/30 rad/sec
where n= rpm of the driving disc.
Let the angle of engagement of Geneva disc with the pin be 2φ.
As the pin enters Geneva disc tangentially with no shock,
φ + θ = π/2
φ = π/z ; z= number of slots
Since Z=6, φ = 30 °
hence θ = 60 °
In triangle PGD
R= PD tan 60°
R= 50 tan 60 ° (PD = 50 mm)
R= 86.6 mm
Therefore, Diameter of Geneva Disc = 173.2mm
Mathematical calculations

13. Geneva Disc/Wheel
The geneva disc is made by
making 6 radially equidistant
rectangular slot on a flat disc
with diameter 173.2 (as
calculated) and thickness 8 mm.
It has a circular hole of radius
12.5 mm in the middle to lock the
shaft that connects the geneva
disc with the Turret.
Geneva Disc/Wheel

14. Pin with Pin Disc

15. Geneva Shaft

16. 6 Tools that can be Mounted o n the Turret Head are
1) Single Point Cutting Tool
2) Drilling Tool
3) Boring Tool
4) Knurling Tool
5) Threading Tap
6) Reamer

17. Assembly and Simulation in Creo Parametric 3.0

18. Discussion
Advantages:
 It is the simplest and least expensive intermittent motion mechanism.
 It has wide variety of sizes.
 They have good motion curve characteristics
 It maintains a good control of its load at all time.
 Geneva maintains good control of its load at all Times since it is provided
with locking system.
 Has a very long lifespan.

19. Disadvantages:
 Geneva mechanism is not a versatile mechanism.
 Its acceleration curves start & end with finite acceleration and
deceleration.
 They produce jerks.
 Very difficult to change once design is chosen.

20. At the start of the index motion,the pin is normal to the slot.Hence
α+β=90°,when a is the angular position of Geneva disc and β is the
angular position of driving disc with respect to the line joining the
centres
At any other angular position of the geneva disc,
tan ψ = rsinφ/e−rcosφ
Velocity Analysis of Geneva Mechanism

21. W: Angular velocity of geneva
disc.
ω: Angular Velocity of pin disc=
Constant

22. Acceleration Analysis of Geneva Disc
At two points there is a sudden change in acceleration(sharp
turns).Hence jerk will be produced at these two points only.
Forφ=-φ,cos (-φ)=cos φ, but sin(-φ)=-sin φ.Hence ε can either be
positive or negative depending upon the sign of φ while W is always
positive.

23. MATERIAL SELECTION
 Mild Steel Grade ASTM A36
 Price:India = ₹150/kg
 exhibits excellent welding properties
 Good Machinability
 High Tensile Strength,
Ultimate 400 – 550 MPa
Yield 250 Mpa
 Commonly availabe
in the market
Carbon, C 0.25 - 0.290 %
Copper, Cu 0.20 %
Iron, Fe 98.0 %
Manganese, Mn 1.03 %
Phosphorous, P 0.040 %
Silicon, Si 0.280 %
Sulphur, S 0.050 %

24. FABRICATION PROCESSES
COMPONENTS MACHINE TOOL
Geneva Disc Vertical Milling Machine with End Mill
Cutter
Geneva Shaft Centre Lathe
Pin Centre Lathe
Pin Disc Vertical Milling Machine
Turret Centre Lathe
Miscellaneous Drilling machine
Assembly
The stepped ends of the 2 shafts, connecting the turret with the geneva disc
and pin disc with the prime mover can be press fitted with the
corresponding holes.The shafts will be be put inside Roller Ball Bearing with
25mm I.D, 62mm O.D and housed to the turret slide.

25. CONCLUSION
 So we have discussed in details how the Geneva mechanism is
used to index the turret head of a lathe However, the mechanism
has various shortcomings
 A working model of this will be fabricated and detailed analysis
and testing of the model will be performed.

26. Acknowledgement
We would like to express our gratitude towards Prof. (Dr.)
Jyotirmoy Saha for providing us with the opportunity to work
under his guidance. We are also indebted towards the
Mechanical Engineering Department of Heritage Institute of
Technology for providing us with the required infrastructure.