Download - 88968897 Screw Jack Report (1)
Engineering Design
Group 15
Richard Kempin 379467
Adriano Sanchez 637604
Yacoub Anand 407357
Timothy Kolade 477008
Contents 1. Design Brief and Specification .................................................................................................................................. 4
1.1. Learning Outcomes ........................................................................................................................................... 4
1.2. Design Brief ....................................................................................................................................................... 4
1.3. Specification ...................................................................................................................................................... 4
1.4. Task Allocation Gantt Chart .............................................................................................................................. 5
2. Survey, Design Types and Operation applications .................................................................................................... 6
2.1. Screw Jack Survey ............................................................................................................................................. 6
2.2. Types of Screw Jack ........................................................................................................................................... 6
3. Existing Design Analysis ............................................................................................................................................ 7
4. Concept Design Analysis ........................................................................................................................................... 8
4.1. Variant 2 Analysis .............................................................................................................................................. 8
4.2. Variant 2 Parts Description ............................................................................................................................. 10
4.3. Concept 1 ........................................................................................................................................................ 11
4.3.1. Concept 1 Description ................................................................................................................................. 11
4.4. Concept 2 ........................................................................................................................................................ 12
4.4.1. Concept Description .................................................................................................................................... 12
4.5. Final Concept................................................................................................................................................... 13
4.5.1. Final Concept Analysis ................................................................................................................................. 14
4.6. Part Design Considerations ............................................................................................................................. 15
5. Material and Manufacturing Selection and Jestification ........................................................................................ 16
5.1. Material Survey ............................................................................................................................................... 16
5.2. Material Justification....................................................................................................................................... 17
5.3. Manufacturing Justifications ........................................................................................................................... 18
5.4. Welding Method Survey ................................................................................................................................. 19
5.5. Welding Method Justifications ....................................................................................................................... 19
6. Thread Survey and Justification .............................................................................................................................. 20
6.1. Thread Survey ................................................................................................................................................. 20
6.2. Thread Requirements ..................................................................................................................................... 21
6.3. Thread Justification ......................................................................................................................................... 21
7. Bearings and Bushes ............................................................................................................................................... 22
7.1. Bearings ............................................................................................................................................................... 22
7.1.1. Bearing Survey ................................................................................................................................................ 22
7.1.2. Bearing Justification ........................................................................................................................................ 22
7.2. Bushes ................................................................................................................................................................. 23
7.2.1. Bush Survey ..................................................................................................................................................... 23
7.2.2. Bush Justification ............................................................................................................................................ 23
8. Bearings and Bushes ............................................................................................................................................... 24
8.1. Nut Survey ........................................................................................................................................................... 24
8.2. Locking Nut Justification ..................................................................................................................................... 25
The nylon locking nuts have been selected to secure the safety plate in position. It is relatively cheap to purchase
this nut than manufacturing. In term of weight is much lighter than the metal nuts. The main advantage of this nylon
locking nut is that it is has resistance to torque. ............................................................................................................ 25
9. Safety Factor Justification ....................................................................................................................................... 26
10. Power Screw Specification .................................................................................................................................. 27
10.1. Power Thread Calculations ......................................................................................................................... 27
10.1.1. Accuracy Screw ....................................................................................................................................... 28
10.1.2. Distance Screw ........................................................................................................................................ 34
11. Nut Design Calculations ...................................................................................................................................... 39
12. Contact Plate ....................................................................................................................................................... 42
13. Contact Plate Housing Calculations .................................................................................................................... 44
14. Housing Desing Calculations ............................................................................................................................... 45
15. Handle Design Calculations ................................................................................................................................. 48
15.1. Accuracy Screw Handle Calculations........................................................................................................... 48
15.2. Distance Screw Handle Calculations ........................................................................................................... 51
16. Handle Design Ergonomics.................................................................................................................................. 53
16.1. Ergonomics Background .............................................................................................................................. 53
16.2. Grip Background.......................................................................................................................................... 53
16.3. Hand Sizes ................................................................................................................................................... 53
16.4. Ergonomic Grip Choice ................................................................................................................................ 54
17. Conclusion ........................................................................................................................................................... 55
1. Design Brief and Specification
1.1. Learning Outcomes
Apply Mechanical Engineering Design and Design for Quality Manufacture;
Appraise the influences of human factor considerations on engineering design;
Demonstrate an understanding of the constraints on the designer;
1.2. Design Brief
Your design group has been commissioned to redesign a hand driven Screw Jack using the main concepts provided in Further Information and according to BS and ISO standards. The client requires an efficient design of a screw jack of general use for supporting machine parts during their repair and maintenance on the shop floor, load capacity of X kN and lifting height of Y m.
1.3. Specification
This project is to redesign a hand driven Screw Jack using specific criteria and adding others. Specific Criteria;
Minimum lifting capacity of 19kN
Minimum lifting height of 0.3m
Safety factor between 3 and 4 Additional Criteria;
Adding additional safety features
Improving the initial design
Making the Screw Jack simple to use
Increase the Screw Jack accuracy The initial design (Variant 2) is a basic Screw Jack design that will be analysed in the report. Improving the Variant 2 design is a task that requires thought about the characteristics of the Jack and the effect of any changes. Some of the characteristics that need to be assessed are;
Existing Screw Jack Types
Materials Used
Thread Used
Screw Diameter
Lifting
Handle
Handle Size and Ergonomics
Safety Factors
1.4. Task Allocation
Task Person Allocated
Group Leader Adriano Sanchez
Secretary Timothy Kolade
Initial research Richard Kempin, Adriano Sanchez, Yacoub Anand, Timothy Kolade
Design brief Richard Kempin
Gantt Chart Adriano Sanchez
Screw Jack Survey Richard Kempin
Existing Design Analysis Richard Kempin
Variant 2 Analysis Richard Kempin, Adriano Sanchez
Conceptual Designs and Analysis Richard Kempin, Adriano Sanchez
Design Considerations Richard Kempin
Material Consideration and Justification Timothy Kolade, Adriano Sanchez, Richard Kempin
Manufacturing Considerations and Justifications Richard Kempin, Adriano Sanchez, Timothy Kolade
Nut Survey and Justification Timothy Kolade
Thread Considerations and Justifications Yacoub Anand, Adriano Sanchez
Bearing and Bush Survey and Selection Richard Kempin, Adriano Sanchez
Safety Factor Determination Richard Kempin
Part Calculations Handle Adriano Sanchez
Housing Adriano Sanchez
Screws Adriano Sanchez
Nut Adriano Sanchez
Contact Plate Richard Kempin
Contact Plate Housings Richard Kempin
Safety Plate Adriano Sanchez
Ergonomics Yacoub Anand
Part Design Handle Adriano Sanchez
Housing Richard Kempin, Adriano Sanchez
Screws Adriano Sanchez
Nut Adriano Sanchez
Contact Plate Richard Kempin
Contact Plate Housings Richard Kempin
Safety Plate Timothy Kolade
Ergonomic Grips Yacoub Anand
Bushes Richard Kempin, Adriano Sanchez
Nut Securing Plate Adriano Sanchez
Detail Drawings Richard Kempin, Adriano Sanchez, Yacoub Anand, Timothy Kolade
Instructional Manual Yacoub Anand, Richard Kempin
Meeting Minutes Timothy Kolade
Report Richard Kempin
2. Survey, Design Types and Operation applications
2.1. Screw Jack Survey
A Screw Jack is a type of jack that is operated by turning a lead screw to lift or hold a weight. The screw jack is an
invention that can be accredited to Leonardo Da Vinci and uses concepts that date back to Archimedes in 2000 BC.
There are various different types of Screw Jacks available that all have their own advantages and disadvantages. This
section will analyse the different types of Screw Jack and how they differ from each other. The simplest way of doing
this is to break down the concepts of a Screw Jack, look at how they differ and then compare a selection of current
models and see how they are used.
2.2. Types of Screw Jack Type of Screw Jack
Description Advantages Disadvantages Common Uses Load Capacities
Supporting Image(s)
Axially Translating Screw Jack
Uses rotary motion of a screw in a nut or a nut in a casing to move the screw axially. Can utilise a worm gear to accommodate different handle designs. Can incorporate bearings to reduce friction.
Simple design
Cheap to manufacture
Cheap to purchase
Wide choice of materials available
Wide choice of size and lifting capacity
Limited operational ability
Cheaper manufactures use cheaper/weaker materials
Lack of bearings make it hard to use and increase wear
Machinery alignment
Lifting of portable buildings (multiple jacks used in parallel)
Used on construction sites as cable jack
5kN to 1000kN
i
depending on model
Figure 2.1
Rotating Screw with Traveling Nut
As the screw is rotated, the Loading Nut will travel up or down the screw depending on the direction of rotation. Can utilise a worm gear to accommodate different handle designs. Can incorporate bearings to reduce friction.
Very simple design
Cheap to manufacture
Wide choice of load capacity and Screw lengths
Wide choice of materials available
Cheap to purchase
Loading Nut requires force acting upon it to prevent it turning with the Screw.
Excess lubrication may counter the effect of self-locking thread
Total jack size fixed at maximum.
Machinery alignment
Linear actuator
Micrometers
5kN to 1000kN
ii
depending on model
Figure 2.2
Scissor Jack
As the screw rotates in a horizontal direction, it causes the scissor design to squeeze together raising its height.
Very simple design
Very cheap to manufacture
Light weight
compact
Wide choice of materials available
Requires regular lubrication or high likelihood of locking.
Lifting cars to replace tyres
Max load 19kN to 40kN
iii
depending on model
Figure 2.3
i www.techdrives.co.uk ii www.techdrives.co.uk
iii www.4x4jack.com
3. Existing Design Analysis
All Screw Jacks will suffer from common hazards as well. These include;
Shearing of threads
Crushing of weaker parts
Exposure to corrosive substances
Instability (damaged Housing or uneven ground)
Human errors:
Misuse such as kicking handles
Dropping
Excessive loading
Impact loading
Over lubrication
All Screw Jacks will have to consider common design requirements such as;
Safety factors
Manufacturing costs
Ergonomics
Material stresses and strengths
Type of Screw Jack
Cost Range (£ per unit)
Ease of Operation and Operation Requirements
Hazards Design Requirements
Axially Translating Screw Jack
£150 to £5000i
depending on model requirements
Simple to operate
Requires upper body strength
Can be hard to turn handles depending on handle length/size
Human factors such as kicking the handle when friction is too great
Wear on the screw may cause the self-locking attributes to fail.
May require bearings to prevent the load turning with the screw
Self-locking screw
Handle ergonomics
Handle length (from centre)
Friction to overcome.
Bearing requirements
Rotating Screw with Traveling Nut
£64.11 ($100US)
ii to
£128.22 ($200US)
iii
depending on model requirements
High level of strength requirement to turn screw when plate is loaded
Can be hard to turn handles depending on handle length/size
Plate will not turn if not loaded
Limited contact area for load
Uneven loading may cause uneven wear
Self-locking screw
Load friction
Handle length (from centre)
Required force
Plate strength
Methods of fixing load to plate
Scissor Jack
£7.44iv to
£297.20v
depending on model requirements
Very simple to operate
Requires significant levels of upper body strength when loaded
Compact and easily storable when unused
Can cease if unused and un-lubricated
Can cause injury if used incorrectly
Light weight
Self-locking screw
Compact
i www.screwjack.en.alibaba.com ii www.alibaba.com
iii www.alibaba.com
iv www.valuemedia.co.uk
v www.jtote.com
4. Concept Design Analysis
4.1. Variant 2 Analysis
Figure 4. 1
Variant 2 Drawing 1
Bolt and Safety Plate
Nut
Securing Screw
Screw and Nut Threads
Screw
Housing
Figure 4. 2
Variant 2 Drawing 2
4.2. Variant 2 Parts Description
Nut This is the threaded Nut that the screw rotates in. It is fixed in place in the Housing by Securing Screws. If the Screw is rotated, the stationary nut will force the Screw either up or down depending on the direction of rotation. The Nut will need to be capable of supporting the load without shearing or buckling. As a separate part to the Housing and Screw, it is replaceable. Securing Screw This is a screw that secures the Nut into the Frame ensuring it does not rotate or fall out. This part is not load bearing and is usually batch ordered. Housing This is the outer shell of the Screw Jack. It houses the Nut and acts as a base for the Screw. The main purpose of the Housing is to transfer the load transmitted to the screw through to the ground. It also acts as a casing for the Screw when not in use. This is a large piece that requires to be made from a strong material. Due to its size it will need to be cast. It has to tapped holes in the side for the Securing Screws. Screw This is the load bearing part of the Screw Jack. When it is rotated it will either raise or lower (depending on the direction of rotation) adjusting the height of the Screw Jack. This is probably the most important part of the Screw Jack. If the Screw fails, the entire Jack is unusable. The screw thread can come in different types depending on the requirements of the screw. These will be discussed later. This part must also be able to withstand the load put on the Jack without sheering or buckling. These characteristics are dependent on the thread thickness, thread depth and Screw diameter. Bolt and Safety Plate These are two pieces attached to the bottom of the Screw as a safety feature. The Washer is bolted to the Screw using a Bolt in a pre-taped hole in the bottom of the Screw. The washer will have a wider diameter than the Screw as so to not travel past the Nut preventing the Screw travelling too far out of the Piece. This will be set at the Screws maximum length as to prevent any accidents. Contact Plate (Arial and horizontal view) The Contact Plate will be in contact with the load. This design is cone shaped as to give it a greater surface area contact with the load. This also allows the centre of the cone to be hollow so it can be bolted to the Handle Carrier. Depending on the dimensions of the design, this could also incorporate a bearing bellow it allowing it to rotate if needed. The wide surface area will also allow for uneven loads. Handle Carrier (Internally Threaded) This piece is connected to both the Screw and the Cone. It has a threaded hole through it for the handle to be attached in. It can be connected to the Screw and Cone either by welting or threading. This piece must be able to withstand both the load on the Jack as well as the force applied through the handles. Handle This is the method used to turn the Screw. It is threaded in the centre allowing it to be fixed in position within the Handle Carrier. The handle is designed to withstand bending from the force exerted upon it from the user.
4.3. Concept 1
4.3.1. Concept 1 Description
The Nut is bolted into the Housing from above using Securing Bolts. The Screw is rotated in this by
the Handle. The Handle is attached at the top of the Screw through a Handle Carrying Attachment.
The contact plate is attached above the Handle Carrying Attachment with Bearings between. The
Bearings will allow the Contact plate to rotate freely under load as required relieving the turning
friction.
Figure 4. 1
Initial Concept Drawing
4.4. Concept 2
4.4.1. Concept Description
This design has two Screws. A Distance Screw and an Accuracy Screw. The Distance Screw will lift the
load a specific height in a fewer turns than the Accuracy Screw which will be used to raise the load
accurate amounts. The Distance Screw rotates in the Nut, which is bolted into the Housing, by the
handle attached at the top of the Screw. The Accuracy Screw rotates inside the Distance Screw
(threaded hole inside the Distance Screw) and is rotated by the handle attached at the top of the
Screw. The contact Cone is attached above the Accuracy Screw on Bearings.
Figure 4. 2
Concept Drawing 2
4.5. Final Concept
Figure 4. 3
Final Concept Drawing
Housing
Handle
Screw
(Distance)
Handle
Carrying
Attachment
Weld
Bolt Securing
Plate
Bearings
Un-Threaded
Screw
Screw
(Accuracy)
Handle
Contact
Plate
Bearings
Nut
Securing
Cap
Securing
Cap Bolt
Plate
Housing
Grub Screw
NOT TO SCALE
Bolt
4.5.1. Final Concept Analysis
Bearings
Three sets of Bearings. The uppermost will take the load on the Jack and allow the Contact Plate to rotate
freely if required. The middle Bearings are designed to reduce the friction caused by the Nut Securing Cap
pushing on the Nut. The lowest Bearings will take the entire load placed on the Jack while it is rotating. It will
be placed between the Nut and the Housing allowing the Nut to be rotated without friction.
Contact Plate
A cylindrical piece with a grove towards the bottom and an internal hole to save material. It is designed to
withstand the load on the Jack. It sits on a Bearing inside the Contact Plate Housing. The grove is for Grub
Screws to keep it in the housing. The top surface will be hatched to give it better grip.
Contact Plate Housing
Houses the Contact Plate and the bearing. Has taped holes through it for Grub Screws to keep the Contact
Plate in place. It is welded to the Accuracy Screw.
Grub Screw
Placed through the Contact Plate Housing and into the grove of the Contact Plate to prevent the Contact
Plate from falling out or being accidentally removed. This part is not load bearing.
Handle
Two sets of handles. One welded to the top of the Accuracy Screw (Unthreaded section) to turn the Accuracy
Screw. The other welded to the Nut to rotate it. The sizes are determined by the amount of force applied on
them. They will also have ergonomic handles for the user.
Housing
The main body of the Jack. This houses the Distance Screw when it is not extended. Has an open bottom
allowing the Distance Screw to be removed from bellow. Has taped holes in the top for the Securing Cap
Bolts. Contains a ridge inside as a platform for the Bearings.
Nut
As the nut rotates, it pushes the screw up or down. It sits inside the Housing on Bearings and secured by the
Nut Securing Cap (between a Bush). Has Handles welded to it in order to rotate it.
Nut Securing Cap
Bolted to the Housing by the Securing Cap Bolts. Pushes on the Nut (via Bush) holding it in the Housing.
Screw (Accuracy)
This is the smaller Screw that lifts the Jack small amounts for every turn(one turn raises the Jack 5mm). It sits
in the Distance Screw. Has an unthreaded section at the top for the Handles to be welded to. The Contact
Plate Housing is bolted to the top.
Screw (Distance)
This is the larger Screw that lifts the Jack further for each turn (one turn raises the Jack 16mm). Sits in and is
rotated by the Nut. Has a threaded hole in the top for the Accuracy Screw. Has a Securing Plate bolted to the
bottom to prevent it from being removed while in use.
Securing Cap Bolt
Used to bolt the Nut Securing Cap to the Housing.
Securing Plate
Metal plate bolted to the bottom of the Distance Screw. Its diameter is wider than the Distance Screw and
had 4 keys as part of the design that will run in the channels cut into the housing to prevent the Distance
Screw from turning. The Securing Plate will contact the housing in the event the Distance Screw is extended
beyond its limit. Its purpose is to prevent the Screw from being removed too far from the Nut compromising
the safety of the Jack.
4.6. Part Design Considerations
Part Design Considerations
Bearings To bear the dynamic load on the Jack
To reduce friction
Bearing
Bushes
To prevent wear on the Bearings
Fast wearing material
Easy to replace
To fail before the Bearings
Contact
Plate
To withstand the load without receiving damage
To fail before the Contact Plate Housing
Be removable
Easy to remove or replace
Cheap to manufacture
Contact
Plate
Housing
To fail after the Contact Plate
To hold the Contact Plate and Bearing
Withstand the load on the Jack
Handles Long enough to overcome the torsion of the Jack
Thick enough to withstand bending from force applied to it
Ergonomic design
Housing Strong enough to withstand the load on the Jack
Wide enough for stable base
To house and protect bearings and Screws from damage
Machined key channels to keep the Distance Screw aligned
Nut High enough for welded handles
Self-locking thread
Nut
Securing
Cap
To hold the Nut in place
Prevent the Nut and Bearings from being accidentally removed from the Housing
Screw
(Accuracy)
Self-locking thread
Unthreaded section for welded handles
Close pitch for accurate distance per turn
Withstand the load without buckling
Screw
(Distance)
Self-locking thread
Internal thread for Accuracy Screw
Larger pitch for greater distance per turn
Withstand the load without buckling
Securing
Plate
Wider that Distance Screw
Strong enough to withstand low level impact when in use
Machined keys to keep the Distance Screw aligned
5. Material and Manufacturing Selection and Jestification
5.1. Material Survey
Material Specific Code
Standard Yield Stress (N/mm
2)
Manufacturing Options
Common Uses General Properties
Brass
CZ121 BS 2874 150-400 Milling
Lathing
High speed machined components
Locks
Hinges
Hard and durable at low temperatures
East to machine
Non sparking
Corrosion resistant
Machinability = 100
High metal removal rate
High metal removal rate
CZ128 BS 2874 150-380 Milling
Lathing
Pistol firing pins
Jewellery
Horse shoes
Low Carbon Steel (Cold drawn)
220M07 BS 970:1991
355-465 Milling
Lathing
Machinery parts
Wires
Sprocket and chain assemblies
Explosive forming tools
Dies/Bolts/Rods
Cheap
Low Tensile Strength
Malleable
Increasable surface hardness
Medium Carbon Steel
AISI 1045 BS 970:1991 IS:9001:2000
505 Milling
Lathing
Vehicles
Shafts
Bushings
Crankshafts
Connecting rods
Expensive to manufacture
Durable
Hardened through flame or induction
Welding not through flame
High Carbon Steel (Manganese)
EN31 BS 970:1991 IS:9001:2000
>600 Milling
Lathing
Tool manufacture
Specialist requirements
Very strong
Expensive
Machinability = 40
Austenitic Stainless Steels (Softened)
303S31 BS 970:1991
>190 Milling
Lathing
Screws
Gears
Aircraft fittings
Bushings
Shafts
Machinability = 16
Low metal removal rate
Grey Cast Iron
FG 200 IS:210 1978 200 Casting Automotive part manufacture
Cooking utensils
Construction materials
Hard to machine
Sand casting
Hard wearing
Titanium Ti-6Al-2Sn-4Zr-6Mo
ASTM B 265 ASTM B 338 ASTM B 367
1100 Casting
Forging
Milling
Gas turbine engines
Helicopter rotors
Spacecraft
Golf clubs
Bicycle frames
Extremely strong and hard wearing
Very expensive
Light weight
Corrosion resistant
Aluminium bronze
CA104 BS 2874 EN 12163
370 Milling
Lathing
Valve and pump components
Fasteners
Engine components
Cheap
Light weight
Easy to machine
Aluminium Alloy
6063 BS EN 12020-1:2008
62-172 Milling
Lathing
Stamping
Casting
Architectural applications
Window frames
Doors
Irrigation tubing
Light weight
Easy to machine
Corrosive resistant
5.2. Material Justification
Part No
Component Name
Material Section
Quantity Material Justification
1 Contact Plate Mild Steel 220M07 BS970:1991 (IS:9001:2000)
1 Low cost
Economical to machine
Will fail before Contact Plate Housing
2 Contact Plate Housing
Medium Carbon steel AISI 1045 BS970:1991 (IS:9001:2000)
1 Can be cast for complex shape
Will fail after Contact Plate
Can be machined for tolerance fits
3 Handles Medium Carbon steel AISI 1045 (IS:9001:2000)
4 Material available in rolled bars
Strong enough to withstand bending force
4 Handle Grips Natural Moulded Rubber BS 3734
4 Ergonomic material
Vibration absorbing
Economic to manufacture
5 Housing Grey cast iron FG 200 (IS:210 1978)
1 Can be cast for complex shape
Strong enough to hold load on Jack
Economical to manufacture
6 Nut Medium Carbon steel AISI 1045 BS970:1991 (IS:9001:2000)
1 Strong enough material to withstand the load on the jack
Practical to manufacture
7 Nut securing cup
Brass CZ128 BS 2874
2 Low cost
Economic to manufacture
Hard and durable at low temperatures to protect the nut assembly
8 Screws ( Accuracy)
Medium Carbon steel AISI 1045, BS970:1991 (IS:9001:2000)
1 High yield strength
Screws will not bend or buckle
Threads unlikely to strip
Can be welded to 9 Screw
( Distance) Medium Carbon steel AISI 1045 BS970:1991 (IS:9001:2000)
1
10 Securing Plate Mild steel 220M0 BS970:1991 (IS:9001:2000)
1 Low force requirements on part
Can be machined for key sections
5.3. Manufacturing Justifications
Part Manufacturing Method Justification
Contact Plate Sand Casting Turning/Milling
Sand Casting will give a suitable surface finish of 12.5µm
Required Surfaces can be machined for suitable finishes of 6.3µm and 1.6 µm
Contact Plate Housing Die Casting Turning/Milling
Die Casting will give a suitable surface finish of 0.8µm for the inside dimensions ready for use
Required Surfaces can be machined for suitable finish of 6.3 µm
Handles Cold rolling, drawing Grinding
Cold rolling steel will give a surface finish of 3.2µm
Grinding the end that will be welded will have a finish of 3.2µm
Handle Grips Injection Moulding An economical manufacturing method that will mass produce the parts ready to use
Housing Sand Casting Sand casting will give a cheap surface finish of 25µm allowing for sand blasting or painting if required
The inside requires a better finish of 12.5µm for the fit with the bush
Nut Turning Milling
The inside will need to be threaded by turning
The smaller outer diameter will be turned then grinded to surface finish of 3.2µm for welding
The larger outside diameter will be turned to a surface finish of 3.2µm due to the fit with the bush
Nut Securing Cap Turning Required surface finish of 6.3µm due to outer exposure to user and inner fit with bush
Screw (Accuracy) Turning Grinding
Turning for the thread
Grinding the unthreaded section to a finish of 3.2µm for welding of Handles
Screw (Distance) Turning Grinding
Turning for the outer thread and inner thread
Grinding the underside to a finish of 3.2µm for welding of Securing Plate Bolt
Securing Plate Milling Milling for accurate fits and tolerances for the keys
5.4. Welding Method Survey Name Characteristics Applications Justification
Brazing This mechanical joining process, that use fillers having a significantly higher melting points ( 450 to 800o )
The process is used widely for mechanical joining and sealing for higher performance applications on copper based alloys
This kind of processes are to slow and they are most widely used on copper alloys
Gas Welding
The heat to produce fusion of the parent metal and filler rod is provided by burning a suitable gas in oxygen or air, since it burns in oxygen and gives a high flame temperature of 3100o - 3200o. C.
It is widely used for welding pipes and tubes, as well as repair work
The speed of this process makes it too slow for the welding of the handles, rising cost.
Metal Arc Welding
In this process an arc is drawn between a coated consumable electrode and the work piece. The metallic core-wire is melted by the arc and is transferred to the weld pool as molten drops.
The process is generally limited to welding ferrous materials, though special electrodes have made possible the welding of cast iron, nickel, aluminum, copper, and other metals
The seller recommend welding the material under especial considerations as this kind of welding processes, enable to use low hydrogen electrodes, it will be the one being use to weld the handles
MIG Welding
This process is used widely for automated welding using robots. The metal inert gas process uses a consumable electrode of wire form and an inert gas shield of carbon dioxide when welding carbon steel
Was originally developed for welding aluminum and other non-ferrous materials in the 1940s, however, was soon applied to steels because it allowed for lower welding time compared to other welding processes
This process is suitable to weld the handles but rise the production cost due to the prices of inert gas.
TIG Welding
This process was developed for welding magnesium, even though, it is now used for welding aluminum, copper, stainless steel, and a wide range of other metals that are difficult to weld.
It is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminum, magnesium, and copper alloys
This process is suitable to weld the handles but rise the production cost due to the prices of inert gas.
Submerged Arc Welding
This process involves the welding arc being continuously submerged under a mound of granular flux. The resulting weld is uniform with good physical and chemical properties.
This process got a wide range of welding applications such as; carbon steels, low alloy steels, stainless steels and nickel-based alloys.
The process is suitable to weld the handles but the slowness of the welding rise the cost.
Electron Beam Welding
A concentrated beam of electrons bombards the base metal, causing it to melt and fuse. Therefore the process is most efficient when done in a vacuum chamber
This process is able to melt any known material and the ability to weld dissimilar metals
The process is a high quality welding but to get the best from it, it needs the vacuum chamber, so cost are risen
Laser
Welding.
The laser beam is a concentrated beam of light with sufficient energy to generate the heat at the base metal surface to cause fusion.
This is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium.
The use of this process is cost effective but too expensive for the manufacturing process.
5.5. Welding Method Justifications
The Metal Arc Welding process have been selected, because several considerations, such as;
This process is flexible and enables the use of low hydrogen electrodes that the seller recommends
It reduces the cost of manufacturing
Its ideal for repairs as this kind of process are mobile increasing the versatility of it.
6. Thread Survey and Justification
6.1. Thread Survey
Purpose of Power Threads
Transmit force by converting rotational motion into linear motion
There are four main types of Power Thread. Below are the characteristics;
Figure 6.3
Buttress Thread
Figure 6.1
Trapezoidal Thread
Figure 6.2
Square Thread
Figure 6.4
Ball Screw Thread
Thread Type Characteristics Advantages Disadvantages Supporting Images
Acme (Trapezoidal) Most common form of Power thread
Trapezoidal and Acme threads have a difference of 1°
Economic to manufacture
Higher load capacity
Can be self-locking
Low efficiency thread
Resultant Radial pressure/side thrust
Figure 6.1
Square Used for power/force transmission
Low friction
No imposed radial forces
High efficiency
Radial pressure/side thrust imposed on the nut.
Can be self-locking
Difficult and expensive to manufacture
Low thread thickness results in low load capacity
When worn, cannot be repaired. Only replaced
Figure 6.2
Buttress Combines the advantages of square and trapezoidal threads
Used for heavy unidirectional axial forces
High Efficiency
Economic to manufacture
Can be self-locking
It can only transmit power in one direction
Figure 6.3
Ball Screw Uses ball bearings to reduce friction and distribute force
Used in accurate machinery alignment
Very low friction
Highly accurate
Low load capacity
Expensive to manufacture
Not self-locking
Figure 6.4
6.2. Thread Requirements
Displace load axially, minimum requirement is one direction
Limited Friction
Self locking
Economical to manufacture
Load bearing threads
6.3. Thread Justification
Thread Surface Both Screws (alternate directions)
Chosen Thread Buttress Thread
Reason Low Friction
High load bearing capacity
Economic to manufacture
Only one direction load direction required
Table 6. 2
Thread Type Justification
Research source – design of Machine Elements, Third Edition, 2010, V.B Bhandari
7. Bearings and Bushes
7.1. Bearings
7.1.1. Bearing Survey
There are many types of bearings available for use today and they all have their own specific characteristics and
reasons for use. This survey will look at the different types and their properties
Bearing Type Advantages Disadvantages Uses
Thrust Ball Bearing Capable of taking high dynamic loads
Low cost
Internal clearance for alignment
Can only take load in one direction
Cannot take radial load
Plant machinery
Pumps
Thrust shafts
Roller Bearing Can take radial load
High radial load capacity
Cannot take axial loads
Take up more room than needle roller bearings
Transmissions
Printing
Motorcycles
Needle Roller Bearing
Take less space
High load capacity
Can only take load in one direction
Cannot take radial load
Wider than Roller Bearings for same capacity
Precision applications
Gearboxes
Automotive differentials
Tapered Roler Bearings
Very High Load capacity
Efficient design
Very expensive
Minimum size requirements
Trailer and Caravan axles
Transmissions
7.1.2. Bearing Justification The chosen bearings used will be Thrust Bearings. The reason for this will be the cost and axial load efficiency of the
bearings. We have chosen to use a bearing with dimensions 50x95x31 for the Nut load bearing (dynamic load
capacity of 88.4kN) and a bearing with dimensions 50x95x31 for the Contact Plate bearing (dynamic load capacity of
55.3kN) and
Figure 7. 1
Needle Roller Bearing
Figure 7. 2
Tapered Roller Bearing
Figure 7. 3
Roller Bearing
7.2. Bushes
7.2.1. Bush Survey
Types Description Characteristics
Solid sleeve
A bush is an independent plain
bearing that is inserted into a
housing to provide a bearing
surface for rotary applications.
Solid tube.
Flanged Solid sleeve with a flange extending radially outward from
the outside diameter to provide a thrust surface or used
to allocate the bushing when it is installed.
Split Splits bushes has a cut along its length.
Clenched Clenched bushes have the same cut as split bushes but
with a clench across the cut.
7.2.2. Bush Justification
A split bush has been selected to be placed into the housing between the nut and the cap to absorb the wear as a
solid bearing cannot be placed there. Solid sleves have been selected to be placed between the bearings and their
housings to prevent wear on the walls of the housing. The company “Xingya Non-Ferrous Metal Casting Co., Ltd.” is
able to manufacture the selected bushes.
Figure 7. 4
Thrust Bearing
Figure 7. 5
Solid Sleeve Bush
Figure 7. 6
Flanged Bush
Figure 7. 8
Clenched Bush
Figure 7. 7
Split Bush
8. Bearings and Bushes
8.1. Nut Survey There are many different types of nut available for us to use when securing the Safety plate onto the Distance Screw.
This table will show the different types.
Nuts Materials
Type Mode of operation
Advantages Disadvantages Application Images
Lock nuts
Steel
Locking Nuts Aero tight Stainless 304(M5 Self-locking Nut All Metal (Aerotight) A2 Stainless)A2.
Require a bolt to travel through a space, which is actually too small for its diameter and threads. As the bolt passes into the narrowed area of the nut the nut holds it quite firmly.
i
Allows to hand turn into the bolt for the first turns.
Great temperature resistance (600oC) than nylon insert locknuts.
Withstand vibration
Expensive
Architectural metal work
Construction
Internal marine applications
Figure 8.1
HMSii
Split HMS lock nuts trapezoidal thread to ISO 2903:1993, grade 7H
By tightening the clamping bolt, the slot is narrowed, and the nut located without clearance. The nut has a tight fit on the shaft thread so that it cannot turn.
Does not require No keyway when in use on shaft
Easy to mount
No problem with fretting corrosion during dismounting
Expensive Gears
Flywheels
Shafts
Wind
turbines
Figure 8.2
Nylon lock Nut
DIN986 TUV CERT ISO9001:2000
iii
Tightened in the same manner as a normal steel nut, except the nylon thread inside one end will mould to the thread and grip tight prevent it being shaken or vibrated loose.
It is lighter compare to metal locknut
Does not rust
Does not conduct electricity
Low in cost
Allow reused a limited number of times.
Lock washers are not used with prevailing torque lock nuts
Resistance to torque
Not good for elevated temperature
Not advisable in chemical area
Contaminates of the bolt affect the performance of the nylon
Wheels or axles
Aerospace
Agricultural equipment
Appliances
Vehicles
Figure 8.3
Wing Nut
Zinc plated steel
Metric BZP Wing Nuts M5
It has two wings on it side that grip for easy loosen and tighten by hand
Reduces hand afford during tighten and loosening
Weather resistant
It is considered as a weaker nut because of the arm strength
Loose tightening
Weak material holding
Figure 8.4
Metric BZP Wing Nuts M10
Dome Nut
Zinc plated steel
Metric BZP Dome Nuts M5
It can be hand tide to some extend.
It can be use for all type of application mention in the application
It can be bolted or screw depending on the thread depth.
Car wheels
Bike parts
Engine rocker covers
Figure 8.5
Metric BZP Dome Nuts M10
i www.mymilescity.com
ii www.skf.com
iii www.kaimametal.com
Nuts Materials
Type Mode of operation
Advantages Disadvantages Application Images
Lock nuts
Steel
Locking Nuts Aero tight Stainless 304(M5 Self-locking Nut All Metal (Aerotight) A2 Stainless)A2.
Require a bolt to travel through a space, which is actually too small for its diameter and threads. As the bolt passes into the narrowed area of the nut the nut holds it quite firmly.
i
Allows to hand turn into the bolt for the first turns.
Great temperature resistance (600oC) than nylon insert locknuts.
Withstand vibration
Expensive
Architectural metal work
Construction
Internal marine applications
Figure 8.1
HMSii
Split HMS lock nuts trapezoidal thread to ISO 2903:1993, grade 7H
By tightening the clamping bolt, the slot is narrowed, and the nut located without clearance. The nut has a tight fit on the shaft thread so that it cannot turn.
Does not require No keyway when in use on shaft
Easy to mount
No problem with fretting corrosion during dismounting
Expensive Gears
Flywheels
Shafts
Wind
turbines
Figure 8.2
Nylon lock Nut
DIN986 TUV CERT ISO9001:2000
iii
Tightened in the same manner as a normal steel nut, except the nylon thread inside one end will mould to the thread and grip tight prevent it being shaken or vibrated loose.
It is lighter compare to metal locknut
Does not rust
Does not conduct electricity
Low in cost
Allow reused a limited number of times.
Lock washers are not used with prevailing torque lock nuts
Resistance to torque
Not good for elevated temperature
Not advisable in chemical area
Contaminates of the bolt affect the performance of the nylon
Wheels or axles
Aerospace
Agricultural equipment
Appliances
Vehicles
Figure 8.3
Wing Nut
Zinc plated steel
Metric BZP Wing Nuts M5
It has two wings on it side that grip for easy loosen and tighten by hand
Reduces hand afford during tighten and loosening
Weather resistant
It is considered as a weaker nut because of the arm strength
Loose tightening
Weak material holding
Figure 8.5
Metric BZP Wing Nuts M10
Dome Nut
Zinc plated steel
Metric BZP Dome Nuts M5
It can be hand tide to some extend.
It can be use for all type of application mention in the application
It can be bolted or screw depending on the thread depth.
Car wheels
Bike parts
Engine rocker covers
Figure 8.6
Metric BZP Dome Nuts M10
i www.mymilescity.com
ii www.skf.com
iii www.kaimametal.com
8.2. Locking Nut Justification The nylon locking nuts have been selected to secure the safety plate in position. It is relatively cheap to purchase
this nut than manufacturing. In term of weight is much lighter than the metal nuts. The main advantage of this nylon
locking nut is that it is has resistance to torque.
Figure 8. 1
Steel Lock Nut
Figure 8. 2
HMS Lock Nut
Figure 8. 3
Nylon Lock Nut
Figure 8. 5
Dome Nut
Figure 8. 4
Wing Nut
9. Safety Factor Justification
Safety factors are an integral part of modern design processes. The can be described as a form of
redundancy. The higher the safety factor, the higher the safety redundancy.
The safety factor is usually designed into the part from the start. This chosen safety factor will be
determined by the type of product being designed. Low safety factors (between 1 to 2) are usually
used for simple designs with very little risk. The type of material, the manufacturing process, the
purpose and the usage environment will also impact on the safety factor. If the materials are known
and have been tested, the loads and stresses are constant and low, the exposure to weather and
corrosive substances limited then the designed safety factor can be low. If however , these factors
can change or are unknown then the safety factor will need to be higher. The purpose of the
designed piece can also raise the safety factor. For example; impact, high speed or vibration
characteristics will raise the required safety factor to above 5.
The design for this screw jack will have a minimum safety factor of between 3 and 4. The only
exception to this will be the safety factor of the Bearings which will have a dynamic safety factor of
at least 1.5. Unlike the environmental characteristics, which are undeterminable, the material
characteristics are known allowing safety factor will be calculated into the designs of each part. this
will be done on each part by assuming the required load capacity being at least 3 times greater. This
means all parts must withstand of a minimum load of 57kN.
10. Power Screw Specification
10.1. Power Thread Calculations
Calculation Symbol Designation
𝜎𝑦 = 𝑌𝑖𝑒𝑙𝑑 𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑣𝑒 𝑆𝑡𝑟𝑒𝑠𝑠
𝑓𝑠 = 𝑆𝑎𝑓𝑒𝑡𝑦 𝐹𝑎𝑐𝑡𝑜𝑟
𝜎𝑐 = 𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛 𝑆𝑡𝑟𝑒𝑠𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑆𝑐𝑟𝑒𝑤
𝑊 = 𝐿𝑜𝑎𝑑
𝐸 = Young’s Modulus
𝑙 = Lead Distance
𝑃 = 𝑃𝑖𝑡𝑐ℎ 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑑𝑚 = 𝑃𝑖𝑡𝑐ℎ 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟
𝑑𝑐 = 𝐶𝑜𝑟𝑒 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑆𝑐𝑟𝑒𝑤
𝜆 = 𝐿𝑒𝑎𝑑 𝑎𝑛𝑔𝑙𝑒
𝛼 = 𝑜𝑓𝑓𝑠𝑒𝑡 𝑡ℎ𝑟𝑒𝑎𝑑 𝑎𝑛𝑔𝑙𝑒
𝛼𝑛 = 𝑎𝑝𝑝𝑙𝑖𝑒𝑑 𝑎𝑛𝑔𝑙𝑒 𝑛𝑜𝑟𝑚𝑎𝑙
𝐴𝑐 = 𝐶𝑟𝑜𝑠𝑠 𝑆𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝐴𝑟𝑒𝑎
𝐾 = 𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝐺𝑦𝑟𝑎𝑡𝑖𝑜𝑛
𝐿 = 𝑆𝑐𝑟𝑒𝑤 𝐿𝑒𝑎𝑑 𝐻𝑒𝑖𝑔ℎ𝑡 + 𝐻𝑎𝑙𝑓 𝑜𝑓 𝑡ℎ𝑒 𝑁𝑢𝑡 𝐻𝑒𝑖𝑔ℎ𝑡
𝑇 = 𝑇𝑜𝑟𝑞𝑢𝑒
𝜏 = 𝑆ℎ𝑒𝑎𝑟 𝑆𝑡𝑟𝑒𝑠𝑠
𝜎𝑏 = 𝐵𝑒𝑛𝑑𝑖𝑛𝑔 𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑣𝑒 𝑆𝑡𝑟𝑒𝑠𝑠
𝐼 = 𝐴𝑟𝑒𝑎 𝑀𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝐼𝑛𝑒𝑟𝑡𝑖𝑎
𝐽 = 𝑃𝑜𝑙𝑎𝑟 𝑀𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝐼𝑛𝑒𝑟𝑡𝑖𝑎
𝜏𝑚𝑎𝑥 = 𝑀𝑎𝑥𝑖𝑚𝑢𝑛 𝑆ℎ𝑒𝑎𝑟 𝑆𝑡𝑟𝑒𝑠𝑠
𝜏𝑦 = 𝑌𝑖𝑒𝑙𝑑 𝑆ℎ𝑒𝑎𝑟 𝑆𝑡𝑟𝑒𝑠𝑠
10.1.1. Accuracy Screw
𝐷 = 25.97 𝑚𝑚
𝑑𝑚 = 22 𝑚𝑚
𝑑𝑐 = 18.35 𝑚𝑚
𝑃 = 5 𝑚𝑚
𝐻 = 7.9390 mm
𝐻/2 = 3.9695 mm
𝐻1 = 3.75 𝑚𝑚
𝑤 = 1.31920 𝑚𝑚
𝑎𝑐 = 0.589 𝑚𝑚
𝑎𝑐 = 0.589 𝑚𝑚
𝑎 = 0.2236 𝑚𝑚
𝑒 = 1.096 𝑚𝑚
ℎ3 = 4.339 𝑚𝑚
𝑅 = 0.621 𝑚𝑚
Figure 10. 1
Accuracy Screw Buttress Thread Profile
To know the compressive stress allowable for 19000 N, the 𝜎𝑦 needs to be divide for the safety
factor of 3.
𝜎𝑐 = 𝜎𝑦
𝑓𝑠
𝜎𝑐 = 500𝑀𝑃𝑎
3
𝜎𝑐 = 166.67𝑀𝑃𝑎
One of the first approaches to have an idea of which diameter will support the load is to transpose
the formula to make dc the subject
𝜎𝑐 = 𝑊
𝜋4 𝑑𝑐2
𝑑𝑐 = 4𝑊
𝜎𝑐 𝜋
𝑑𝑐 = 4 𝑥 19000𝑁
166.67𝑀𝑃𝑎 𝑥 𝜋
𝑑𝑐 = 12.04𝑚𝑚
Closest core diameter of buttress thread available is 13.058mm.
𝑡𝑎𝑛 𝜆 = 𝑙
𝜋 𝑥 𝑑𝑚 𝑙 = 2𝑃
tan 𝜆 = 8𝑚𝑚
𝜋 𝑥 16.529𝑚𝑚 tan 𝜆 = 0.154 𝜆 = 8.760
𝛼 = 3⁰
𝛼𝑛 = 𝑡𝑎𝑛−1 tan𝛼 𝑥 cos 𝜆 𝛼𝑛 = 𝑡𝑎𝑛−1 tan 30𝑥 cos 8.760
𝛼𝑛 = 2.970
- Self-Locking demonstration:
𝜇𝑠 ≥𝐿 𝑥 cos𝛼𝑛
𝜋 𝑥 𝑑𝑚 0.15 ≥
8𝑚𝑚 𝑥 cos 2.97⁰
𝜋 𝑥 16.529𝑚𝑚
0.15 ≥ 0.154
The screw will not be Self-Locking, for the next calculations the Lead will be take equal to the Pitch
- Buckling Calculations:
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 𝐴𝑐 𝑥 𝜎𝑦 (1 −𝜎𝑦
4 𝑥 𝐶 𝜋2 𝐸 𝐿
𝐾
2
)
𝐶 = 0.25
𝐿 = 120𝑚𝑚 + 1
260𝑚𝑚 𝐿 = 150𝑚𝑚
𝐾 =𝑑𝑐
4 𝐾 =
13.058𝑚𝑚
4 𝐾 = 3.27𝑚𝑚
𝐴𝑐 =𝜋
4 𝑑𝑐2 𝐴𝑐 =
𝜋
4 (13.058𝑚𝑚)2 𝐴𝑐 = 133.92𝑚𝑚2
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 133.92𝑚𝑚2 𝑥 500𝑁/𝑚𝑚2 (1 −500𝑁/𝑚𝑚2
4 𝑥 0.25 𝑥 𝜋2 207𝑥103𝑁/𝑚𝑚2
150𝑚𝑚
3.27𝑚𝑚
2
)
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 32477.2𝑁
As the critical load is less than three times the required load (to allow for safety factor), the chance
of buckling is too high. Therefore this diameter screw is not strong enough. The next diameter we
will try is 16.2mm.
𝐶 = 0.25
𝐿 = 120𝑚𝑚 + 1
260𝑚𝑚 𝐿 = 150𝑚𝑚
𝐾 =𝑑𝑐
4 𝐾 =
18.35𝑚𝑚
4 𝐾 = 4.59𝑚𝑚
𝐴𝑐 =𝜋
4 𝑑𝑐2 𝐴𝑐 =
𝜋
4 (18.35𝑚𝑚)2 𝐴𝑐 = 264.46𝑚𝑚2
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 264.46𝑚𝑚2 𝑥 500𝑁/𝑚𝑚2 (1 −500𝑁/𝑚𝑚2
4 𝑥 0.25 𝑥 𝜋2 207𝑥103𝑁/𝑚𝑚2
150𝑚𝑚
4. .59𝑚𝑚
2
)
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 97632.11𝑁
As this critical load exceeds the safety factor of three times the required load, there will be no
chance of buckling. The resultant safety factor is 5.14.
𝑡𝑎𝑛 𝜆 = 𝑙
𝜋 𝑥 𝑑𝑚 𝑙 = 𝑃
tan 𝜆 = 5𝑚𝑚
𝜋 𝑥 22𝑚𝑚 tan 𝜆 = 0.07 𝜆 = 4. .140
𝛼 = 3⁰
𝛼𝑛 = 𝑡𝑎𝑛−1 tan𝛼 𝑥 cos 𝜆 𝛼𝑛 = 𝑡𝑎𝑛−1 tan 30𝑥 cos 4.550
𝛼𝑛 = 2.990
- Self-Locking demonstration:
𝜇𝑠 ≥𝐿 𝑥 cos𝛼𝑛
𝜋 𝑥 𝑑𝑚 0.15 ≥
5𝑚𝑚 𝑥 cos 2.99⁰
𝜋 𝑥 20𝑚𝑚
0.15 ≥ 0.08
This demonstrates, the accuracy screw is self-locking.
- Tangential forces:
Σ𝐹𝑡 = 0; 𝑞 − 𝑛 𝜇𝑠 𝑥 𝑐𝑜𝑠𝜆 + 𝑐𝑜𝑠𝛼𝑛𝑥 𝑠𝑖𝑛𝜆 = 0
𝑞 = 𝑛 ( 𝜇𝑠 𝑥 𝑐𝑜𝑠𝜆 + 𝑐𝑜𝑠𝛼𝑛𝑥 𝑠𝑖𝑛𝜆)
- Axial forces:
Σ𝐹𝑎 = 0 ; 𝑊 + 𝑛 𝜇𝑠 𝑥 𝑠𝑖𝑛𝜆 − 𝑐𝑜𝑠𝛼𝑛𝑥 𝑐𝑜𝑠𝜆
Y
X W
Y
n x cos 𝛼𝑛
q
𝑛 = 𝑊
(−𝜇𝑠 𝑥 𝑠𝑖𝑛𝜆 + 𝑐𝑜𝑠𝛼𝑛𝑥 𝑐𝑜𝑠𝜆)
𝑛 =19000 𝑁
(−0.15 𝑥 𝑠𝑖𝑛4.14 + 𝑐𝑜𝑠2.99 𝑥 𝑐𝑜𝑠4.14)
𝑛 = 19285.35 𝑁
𝑞 = 19285.35 𝑁 0.15 𝑥 𝑐𝑜𝑠4.14 + 𝑐𝑜𝑠2.99 𝑥 𝑠𝑖𝑛4.14
𝑞 = 4275.64 𝑁
- Torque to lift the weight:
𝑇 = 𝑞 𝑥 𝑑𝑚
2
𝑇 = 4275.64 𝑁 22 𝑚𝑚
2
𝑇 = 47032.04 𝑁.𝑚𝑚
- Bending:
𝜏 =𝑇 𝑥
𝑑𝑐2
𝐽
𝜏 =47032.04 𝑁.𝑚𝑚 𝑥
18.35𝑚𝑚2
𝜋32 𝑥 18.35𝑚𝑚 4
𝐽𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 =𝜋
32 𝑥 𝑑𝑐 4
𝜏 = 38.77 𝑁/𝑚𝑚2
𝜎𝑏 = 𝑀𝑏 𝑥
𝑑𝑐2
𝐼
𝜎𝑏 = 112.02 𝑁.𝑚𝑚 𝑥
18.35𝑚𝑚2
𝜋64 𝑥 18.35𝑚𝑚 4
𝑀𝑏 = 453 𝑁 𝑥 150𝑚𝑚
𝑀𝑏 = 67950 𝑁.𝑚𝑚
𝐼𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 = 𝜋
64 𝑥 𝑑𝑐 4
𝜎𝑏 = 112.02 𝑁/𝑚𝑚2
𝜏𝑚𝑎𝑥 = 𝜎𝑏2
2
+ 𝜏2
𝜏𝑚𝑎𝑥 = 112.02
2
2
+ 38.772 𝑁/𝑚𝑚2
𝜏𝑚𝑎𝑥 = 68.12 𝑁/𝑚𝑚2
𝜏𝑦 = 𝜎𝑦
2
𝜏𝑦 =500
2 𝑁/𝑚𝑚2
𝜏𝑦 = 250 𝑁/𝑚𝑚2
𝑓𝑠 = 𝜏𝑦
𝜏𝑚𝑎𝑥
𝑓𝑠 = 250 𝑁/𝑚𝑚2
68.12 𝑁/𝑚𝑚2
𝑓𝑠 = 3.67
As the safety factor for bending stress for this diameter is 3.67; this column won’t fail by bending
stress.
𝐷 = 26 𝑚𝑚
𝑑𝑚 = 22.25 𝑚𝑚
𝑑𝑐 = 18.5 𝑚𝑚
𝑃 = 5 𝑚𝑚
10.1.2. Distance Screw
𝐷 = 45.69 𝑚𝑚
𝑑𝑚 = 39.668 𝑚𝑚
𝑑𝑐 = 33.684 𝑚𝑚
𝑃 = 8 𝑚𝑚
𝐻 = 12.7024 mm
𝐻/2 = 6.3512 mm
𝐻1 = 6 𝑚𝑚
𝑤 = 2.11072 𝑚𝑚
𝑎𝑐 = 0.942 𝑚𝑚
𝑎 = 0.2828 𝑚𝑚
𝑒 = 1.828 𝑚𝑚
ℎ3 = 6.942 𝑚𝑚
𝑅 = 0.994 𝑚𝑚
Figure 10. 1
Distance Screw Buttress Thread Profile
As the design is a hollow circle one of the first approach to be taken into account is considering the
minimum thickness, which will be able to support the safety factor of 3, that have been mentioned
before.
𝜎𝑐 =𝑊
2𝜋 𝑥 𝑟 𝑥 𝑡
𝑡 =𝑊
2𝜋 𝑥 𝑟 𝑥 𝜎𝑐
𝑡 =57000 𝑁
(2𝜋 16.84𝑚𝑚 𝑥 166.67 𝑁/𝑚𝑚2
𝑡 = 3.23 𝑚𝑚
The minimum thickness required to support the load without failing for stress is 3.23 mm, so the
diameter could be 32.43mm. However, according to buckling calculations the screw will fail, that is
why an upper diameter have been selected, to give us a major thickness to accomplish bending and
buckling calculations with a safety factor over 3.
- Buckling Calculations
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 𝐴𝑐 𝑥 𝜎𝑦 (1 −𝜎𝑦
4 𝑥 𝐶 𝜋2 𝐸 𝐿
𝑔
2
)
𝐶 = 0.25
𝐿 = 300𝑚𝑚 + 1
2100𝑚𝑚 𝐿 = 350𝑚𝑚
𝑔 =𝑑𝑐
4 𝑔 =
33.684𝑚𝑚
4 𝑔 = 8.421𝑚𝑚
𝐴𝑐 =𝜋
4 (𝑑𝑐)2 −
𝜋
4 (𝐷𝑎𝑐𝑐𝑢𝑟𝑎𝑐𝑦 𝑠𝑐𝑟𝑒𝑤 )2 𝐴𝑐 =
𝜋
4 (33.684𝑚𝑚)2 −
𝜋
4 (25.97𝑚𝑚)2
𝐴𝑐 = 361.42𝑚𝑚2
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 361.42𝑚𝑚2 𝑥 500𝑁/𝑚𝑚2 (1 −500𝑁/𝑚𝑚2
4 𝑥 0.25 𝑥 𝜋2 207𝑥103𝑁/𝑚𝑚2
350𝑚𝑚
8.421𝑚𝑚
2
)
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 104310.3 𝑁
This diameter accomplishes the buckling calculations with a safety factor of 5.49, being secure
enough to be used.
𝑡𝑎𝑛 𝜆 = 𝑙
𝜋 𝑥 𝑑𝑚 𝑙 = 2𝑃
tan 𝜆 = 2(8𝑚𝑚 )
𝜋 𝑥 39.668𝑚𝑚 tan 𝜆 = 0.13 𝜆 = 7.320
𝛼 = 3⁰
𝛼𝑛 = 𝑡𝑎𝑛−1 tan𝛼 𝑥 cos 𝜆 𝛼𝑛 = 𝑡𝑎𝑛−1 tan 30𝑥 cos 7.320
𝛼𝑛 = 2.980
- Self-Blocking demonstration:
𝜇𝑠 ≥𝐿 𝑥 cos𝛼𝑛
𝜋 𝑥 𝑑𝑚 0.15 ≥
16𝑚𝑚 𝑥 cos 2.98⁰
𝜋 𝑥 39.668𝑚𝑚
0.15 ≥ 0.128
This demonstrates, the main screw is self-blocking.
- Tangential forces:
Σ𝐹𝑡 = 0; 𝑞 − 𝑛 𝜇𝑠 𝑥 𝑐𝑜𝑠𝜆 + 𝑐𝑜𝑠𝛼𝑛𝑥 𝑠𝑖𝑛𝜆 = 0
𝑞 = 𝑛 ( 𝜇𝑠 𝑥 𝑐𝑜𝑠𝜆 + 𝑐𝑜𝑠𝛼𝑛𝑥 𝑠𝑖𝑛𝜆)
- Axial forces:
Σ𝐹𝑎 = 0 ; 𝑊 + 𝑛 𝜇𝑠 𝑥 𝑠𝑖𝑛𝜆 − 𝑐𝑜𝑠𝛼𝑛𝑥 𝑐𝑜𝑠𝜆
Y
X W
Y
n x cos 𝛼𝑛
q
𝑛 = 𝑊
(−𝜇𝑠 𝑥 𝑠𝑖𝑛𝜆 + 𝑐𝑜𝑠𝛼𝑛𝑥 𝑐𝑜𝑠𝜆)
𝑛 =19000 𝑁
(−0.15 𝑥 𝑠𝑖𝑛7.32 + 𝑐𝑜𝑠2.98 𝑥 𝑐𝑜𝑠7.32)
𝑛 = 19559.46 𝑁
𝑞 = 19559.46 𝑁 0.15 𝑥 𝑐𝑜𝑠7.32 + 𝑐𝑜𝑠2.98 𝑥 𝑠𝑖𝑛7.32
𝑞 = 5398.73 𝑁
- Torque to lift the weight:
𝑇 = 𝑞 𝑥 𝑑𝑚
2
𝑇 = 5398.73 𝑁 39.668 𝑚𝑚
2
𝑇 = 107078.41 𝑁.𝑚𝑚
- Bending:
𝜏 =𝑇 𝑥
𝑑𝑐2
𝐽
𝜏 =107078.41 𝑁.𝑚𝑚 𝑥
33.684𝑚𝑚2
𝜋32
𝑥 33.684𝑚𝑚 4 − 25.97𝑚𝑚 4
𝐽ℎ𝑜𝑙𝑙𝑜𝑤 𝑐𝑖𝑟𝑐𝑙𝑒 =𝜋
32 𝑥 (𝑑𝑜𝑢𝑡𝑒𝑟
4 − 𝑑𝑖𝑛𝑛𝑒𝑟4)
𝜏 = 22.07 𝑁/𝑚𝑚2
𝜎𝑏 = 𝑀𝑏 𝑥
𝑑𝑐2
𝐼
𝜎𝑏 = 135900 𝑁.𝑚𝑚 𝑥
33.684𝑚𝑚2
𝜋4 𝑥 ((16.842𝑚𝑚)4 − (12.985𝑚𝑚)4)
𝐼ℎ𝑜𝑙𝑙𝑜𝑤 𝑐𝑖𝑟𝑐𝑙𝑒 = 𝜋
4 𝑥 𝑟𝑜𝑢𝑡𝑒𝑟
4 − 𝑟𝑖𝑛𝑛𝑒𝑟4
𝑀𝑏 = 453 𝑁 𝑥 300𝑚𝑚 𝑀𝑏 = 135900 𝑁.𝑚𝑚
𝜎𝑏 = 56.01 𝑁/𝑚𝑚2
𝜏𝑚𝑎𝑥 = 𝜎𝑏2
2
+ 𝜏2
𝜏𝑚𝑎𝑥 = 56.01
2
2
+ 22.072 𝑁
𝑚𝑚2
𝜏𝑚𝑎𝑥 = 35.66 𝑁/𝑚𝑚2
𝜏𝑦 = 𝜎𝑦
2
𝜏𝑦 =500
2 𝑁/𝑚𝑚2
𝜏𝑦 = 250 𝑁/𝑚𝑚2
𝑓𝑠 = 𝜏𝑦
𝜏𝑚𝑎𝑥
𝑓𝑠 = 250
𝑁𝑚𝑚2
35.66𝑁
𝑚𝑚2
𝑓𝑠 = 7.01
As the safety factor for bending stress of this diameter is 7.01; this column won’t fail by bending
stress.
11. Nut Design Calculations - Frictional Torque
𝜇𝑓 = 𝜇𝑡 − 𝜇𝑡 (𝑓 = 0)
𝜇𝑡 (𝑓 = 0) = 𝑊 𝑥 𝑑𝑚
2 𝑥
𝐿𝑒𝑎𝑑 𝑥 cos𝛼𝑛
𝜋 𝑥 𝑑𝑚 𝑥 cos𝛼𝑛
𝜇𝑡 (𝑓 = 0) = 19000𝑁 𝑥 46 𝑚𝑚
2 𝑥
16 𝑚𝑚 𝑥 cos 2.98
𝜋 𝑥 46 𝑚𝑚 𝑥 cos 2.98
𝜇𝑡 (𝑓 = 0) = 48070 𝑁.𝑚𝑚
𝜇𝑓 = 107078.41 𝑁.𝑚𝑚− 48070 𝑁.𝑚𝑚
𝜇𝑓 = 59008.41 𝑁.𝑚𝑚
- Bending Stress
𝜎𝑛 =𝑊
𝐴 𝑛
𝜎𝑛 =19000 𝑁
1357.17 𝑚𝑚2
𝐴𝑛 =𝜋
4 𝐷𝑜𝑢𝑡𝑒𝑟 2 −
𝜋
4 𝐷 2
𝐴𝑛 =𝜋
4 62 𝑚𝑚 2 −
𝜋
4 46 𝑚𝑚 2
𝐴𝑛 = 1357.17 𝑚𝑚2
𝜎𝑛 = 13.99 𝑁/𝑚𝑚2
- Shear stress due to Torque for Lifting
𝜏𝑛 =𝑇 𝑥
𝐷𝑜𝑢𝑡𝑒𝑟2
𝐽𝑛
𝜏𝑛 =59008.41 𝑁.𝑚𝑚 𝑥
62 𝑚𝑚2
1011090.18 𝑚𝑚4
𝐽ℎ𝑜𝑙𝑙𝑜𝑤 𝑐𝑖𝑟𝑐𝑙𝑒 =𝜋
32 𝑥 (𝑑𝑜𝑢𝑡𝑒𝑟
4 − 𝑑𝑖𝑛𝑛𝑒𝑟4)
𝐽ℎ𝑜𝑙𝑙𝑜𝑤 𝑐𝑖𝑟𝑐𝑙𝑒 =𝜋
32 𝑥 62 𝑚𝑚 4 − 46 𝑚𝑚 4
𝐽ℎ𝑜𝑙𝑙𝑜𝑤 𝑐𝑖𝑟𝑐𝑙𝑒 = 1011090.18 𝑚𝑚4
𝜏𝑛 = 1.81 𝑁/𝑚𝑚2
- Principal Shear Stress
𝜏𝑛𝑚𝑎𝑥=
𝜎𝑛2
2
+ 𝜏𝑛2
𝜏𝑛𝑚𝑎𝑥=
13.99
2
2
+ 1.81 2 𝑁
𝑚𝑚2
𝜏𝑛𝑚𝑎𝑥= 7.23 𝑁/𝑚𝑚2
𝑓𝑠 = 𝜏𝑦
𝜏𝑚𝑎𝑥
𝑓𝑠 = 250 𝑁/𝑚𝑚2
7.23 𝑁/𝑚𝑚2
𝑓𝑠 = 34.58
The safety factor of 34.58 says that the nut is totally secure. A nut with a smaller height could have
been used to reduce cost, however, it make the design more than 11.52 times secure, due to the
stress being spread between the threads.
- Transverse Shear Stress (stripping of threads)
𝜏 =𝑊
𝜋 𝑥 𝑑𝑐 𝑥 𝑡
𝜏 =19000 𝑁
𝜋 𝑥 46 𝑚𝑚 𝑥 100 𝑚𝑚
𝜏 = 1.32 𝑁/𝑚𝑚2
𝑓𝑠 = 𝜏𝑦
𝜏𝑚𝑎𝑥
𝑓𝑠 = 250 𝑁/𝑚𝑚2
1.32 𝑁/𝑚𝑚2
𝑓𝑠 = 189.39
- Maximum Allowable Bearing Pressure
𝑆𝑏 = 𝑊
𝜋4 𝑥 𝐷 2 − 𝑑𝑐 2 𝑥 12.5
𝑆𝑏 = 19000 𝑁
𝜋4 𝑥 62 𝑚𝑚 2 − 46 𝑚𝑚 2 𝑥 12.5
𝑍 =𝑡
𝑃
𝑍 =100 𝑚𝑚
8 𝑚𝑚
𝑍 = 12.5
𝑆𝑏 = 1.12 𝑁/𝑚𝑚2
12. Contact Plate
To determine the minimum thickness required for the Contact Plate, first the 𝜎c must be calculated.
𝜎c =𝜎y
𝑓𝑠
𝜎c =355 N/mm2
3
𝜎c = 118.33 N/mm2
From this, the 𝜏𝑦 can be calculated.
𝜏𝑦 = 𝜎𝑦
2
𝜏𝑦 = 355
2
𝜏𝑦 = 177.5 𝑁/𝑚𝑚2
And the maximum allowable 𝜏 (𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 ).
𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 = 𝜏𝑦
𝑓𝑠
𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 = 177.5 𝑁/𝑚𝑚2
3
𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 = 59.17 𝑁/𝑚𝑚2
With this data, the minimum required thickness of the contact plate surface can be calculated.
𝑡 =𝑊
𝜋 𝑥 𝐷 𝑥 𝜏
𝑡 =57000 𝑁
𝜋 𝑥 50 𝑚𝑚 𝑥 59.17 𝑁/𝑚𝑚2
𝑡 = 6.132 𝑚𝑚
This is the minimum thickness. For practicality, the plate will be 57mm high to accommodate for the
Grub screw grove and its requirement to sit in the Contact Plate Housing.
As the Contact Plate will be hollow inside, the buckling stress will have to be calculated for the wall
thickness.
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 𝐴𝑐 𝑥 𝜎𝑦 (1 −𝜎𝑦
4 𝑥 𝐶 𝜋2 𝐸 𝐿
𝑔
2
)
𝐶 = 1
𝐿 = 57 𝑚𝑚
𝑔 =𝑑𝑐
4 𝑔 =
50 𝑚𝑚
1 𝑔 = 50 𝑚𝑚
𝐴𝑐 =𝜋
4 (𝑑𝑐)2 −
𝜋
4 (𝐷𝑎𝑐𝑐𝑢𝑟𝑎𝑐𝑦 𝑠𝑐𝑟𝑒𝑤 )2 𝐴𝑐 =
𝜋
4 (60 𝑚𝑚)2 −
𝜋
4 (50 𝑚𝑚)2
𝐴𝑐 = 863.94 𝑚𝑚2
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 863.94 𝑚𝑚2 𝑥 355 𝑁/𝑚𝑚2 (1 −355 𝑁/𝑚𝑚2
4 𝑥 1 𝑥 𝜋2 200𝑥103𝑁/𝑚𝑚2
57 𝑚𝑚
50 𝑚𝑚
2
)
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 303631.7 𝑁
This allows the walls to be 5mm thick with a safety factor of 16.14
13. Contact Plate Housing Calculations
To determine the minimum thickness required for the Contact Plate Housing, first the 𝜎𝑐 must be
calculated.
𝜎𝑐 = 𝜎𝑦
𝑓𝑠
𝜎𝑐 = 500 𝑁/𝑚𝑚2
3
𝜎𝑐 = 166.67 𝑁/𝑚𝑚2
From this, the 𝜏𝑦 can be calculated.
𝜏𝑦 = 𝜎𝑦
2
𝜏𝑦 = 500
2
𝜏𝑦 = 250𝑁
𝑚𝑚2
And the maximum allowable τ (𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 ).
𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 = 𝜏𝑦
𝑓𝑠
𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 = 250 𝑁/𝑚𝑚2
3
𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 = 83.3 𝑁/𝑚𝑚2
With this data, the minimum required thickness of the Contact Plate Housing can be calculated. The
diameter used is that of the Accuracy Screw. Because of the difference in diameter, the calculation
uses sheer stress.
𝑡 =𝑊
𝜋 𝑥 𝐷 𝑥 𝜏
𝑡 =57000 𝑁
𝜋 𝑥 26 𝑚𝑚 𝑥 83.3 𝑁/𝑚𝑚2
𝑡 = 8.38 𝑚𝑚
This is the minimum thickness. For practicality, the Contact Plate Housing will be 9 mm thick. To
accommodate for the Grub Screw holes, the thickness of the walls will be 11 mm.
14. Housing Desing Calculations
“Minimum thickness for the housing”
𝜎𝑐 =𝑊
2𝜋 𝑥 𝑟 𝑥 𝑡
𝑡 =𝑊
2𝜋 𝑥 𝑟 𝑥 𝜎𝑐
𝑡 =57000 𝑁
(2𝜋 50𝑚𝑚 𝑥 66.67 𝑁/𝑚𝑚2
𝑡 = 2.72 𝑚𝑚
- Buckling Calculations
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 𝐴𝑐 𝑥 𝜎𝑦 (1 −𝜎𝑦
4 𝑥 𝐶 𝜋2 𝐸 𝐿
𝑔
2
)
𝐶 = 0.25
𝐿 = 464 𝑚𝑚
𝑔 =𝑑𝑐
4 𝑔 =
100𝑚𝑚
4 𝑔 = 25 𝑚𝑚
𝐴𝑐 =𝜋
4 𝐷𝑜𝑢𝑡𝑒𝑟
2 −𝜋
4 𝐷𝑖𝑛𝑛𝑒𝑟
2 𝐴𝑐 =𝜋
4 (125 𝑚𝑚)2 −
𝜋
4 (100 𝑚𝑚)2
𝐴𝑐 = 4417.88𝑚𝑚2
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 4417.88𝑚𝑚2 𝑥 200𝑁/𝑚𝑚2 (1 −200 𝑁/𝑚𝑚2
4 𝑥 0.25 𝑥 𝜋2 105𝑥103𝑁/𝑚𝑚2
464𝑚𝑚
25 𝑚𝑚
2
)
𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 = 842456.6
- Safety Factor
𝑓𝑠 = 𝑊𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙
𝑊
𝑓𝑠 = 842456.6 𝑁
19000 𝑁
𝑓𝑠 = 44.34
The safety factor demonstrates that the housing will not fail for buckling.
- Housing Contact Surface Calculations
𝐶 = 2𝜋 𝑥 𝑟
𝐶 = 157.08 𝑚𝑚
𝜎 =𝑀𝑦
𝐼
𝜎 = 57000 𝑁 𝑥 25 𝑚𝑚 𝑥 15 𝑚𝑚
2250 𝑚𝑚4
𝐼 = 1
12 𝑥 𝐵 𝑥 𝐻 3
𝐼 = 1
12 𝑥 1 𝑥 30 𝑚𝑚 3
𝐼 = 2250 𝑚𝑚4
𝜎 = 9500 𝑁/𝑚𝑚2
As the load is being taken between 157 points of 1 mm.
B =1
57000 N
𝜎𝑐𝑖𝑟𝑐𝑢𝑛𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 𝜎
𝐶𝑖𝑟𝑐𝑢𝑛𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑃𝑜𝑖𝑛𝑡𝑠
𝜎𝑐𝑖𝑟𝑐𝑢𝑛𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 9500 𝑁/𝑚𝑚2
157
𝜎𝑐𝑖𝑟𝑐𝑢𝑛𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = 60.51 𝑁/𝑚𝑚2
As the 𝜎𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 = 66.67 𝑁/𝑚𝑚2 for Cast Iron the circumference got the thickness enough to
support the safety factor load of 57000 N.
Figure 15. 1
Handle Force Data
Graph 15. 1
Total Hand Force
Graph 15. 2
Hand Force Pushing Against Pulling (Right and left)
15. Handle Design Calculations
15.1. Accuracy Screw Handle Calculations
Handle Calculations
𝐹ℎ𝑎𝑛𝑑 = 𝑇
𝐿ℎ𝑎𝑛𝑑𝑙𝑒
𝐿ℎ𝑎𝑛𝑑𝑙𝑒 = 𝑇
𝐹ℎ𝑎𝑛𝑑
Total Hand Force
250
300
350
400
180 - 60150 - 90
120 - 12090 - 150
60 - 180
Total Hand Force
Left
Right0
50
100
150
200
250
180150
12090
60
Pull Push Pull Push Pull Push Pull Push Pull Push
L R L R L R L R L R
Angle of application 180 60 150 90 120 120 90 150 60 180
Hand Force 222 151 187 160 151 160 142 187 116 222
Total Hand Force 373 347 311 329 338
According to the graph bellow the optimal length for the handle will be 138.99 mm. as this size cut
the graph in two points. However, there are some manufacturing considerations for the handle and
as it is better and cheaper to produce a handle with a preferred size.
𝐿ℎ𝑚 = 𝐿ℎ − 𝑑𝑐
𝐿ℎ𝑚 = 138.99𝑚𝑚− 18.35𝑚𝑚
𝐿ℎ𝑚 = 120.64 𝑚𝑚
So, the final length will be 125 mm.
110.00
120.00
130.00
140.00
150.00
160.00
373347
311329
338
373 347 311 329 338
Handle Lenght (mm.) 126.09 135.54 151.23 142.95 139.15
Handle Lenght (mm.)
Graph 15. 3
Accuracy Screw Handle Length
Handle bending calculations:
𝜏 =𝑇 𝑥
𝑑𝑐2
𝐽
𝜏 =47032.04 𝑁.𝑚𝑚 𝑥
18𝑚𝑚2
𝜋32
𝑥 18𝑚𝑚 4
𝜏 = 41.07𝑁/𝑚𝑚2
𝐽𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 =𝜋
32 𝑥 𝑑𝑐 4
𝜎𝑏 = 𝑀𝑏 𝑥
𝑑𝑐2
𝐼
𝜎𝑏 = 56625 𝑁.𝑚𝑚 𝑥
18𝑚𝑚2
𝜋64 𝑥 18𝑚𝑚 4
𝜎𝑏 = 98.9 𝑁/𝑚𝑚2
𝐼𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 = 𝜋
64 𝑥 𝑑𝑐 4
𝑀𝑏 = 453 𝑁 𝑥 125𝑚𝑚 𝑀𝑏 = 56625 𝑁.𝑚𝑚
𝜏𝑚𝑎𝑥 = 𝜎𝑏2
2
+ 𝜏2
𝜏𝑚𝑎𝑥 = 98.9
2
2
+ 41.072 𝑁/𝑚𝑚2
𝜏𝑚𝑎𝑥 = 64.28 𝑁/𝑚𝑚2
𝜏𝑦 = 𝜎𝑦
2
𝜏𝑦 =500
2 𝑁/𝑚𝑚2
𝜏𝑦 = 250 𝑁/𝑚𝑚2
𝑓𝑠 = 𝜏𝑦
𝜏𝑚𝑎𝑥
𝑓𝑠 = 3.9
With a safety factor of 3.9, the diameter of the handle demonstrates that will not fail for bending.
Graph 15. 4
Distance Screw Handle Length
15.2. Distance Screw Handle Calculations
Handle Length Calculations
𝐹ℎ𝑎𝑛𝑑 = 𝑇
𝐿ℎ𝑎𝑛𝑑𝑙𝑒
𝐿ℎ𝑎𝑛𝑑𝑙𝑒 = 𝑇
𝐹ℎ𝑎𝑛𝑑
According to the graph bellow the optimal length for the handle will be 316.45 mm. as this size cut
the graph in two points. However, there are some manufacturing considerations for the handle and
as it is better and cheaper to produce a handle with a preferred size.
𝐿ℎ𝑚 = 𝐿ℎ − 𝑑𝑐
𝐿ℎ𝑚 = 316.45𝑚𝑚− 33.684𝑚𝑚
𝐿ℎ𝑚 = 282.77 𝑚𝑚
So, the final length will be 290 mm.
240.00
260.00
280.00
300.00
320.00
340.00
360.00
373347
311329
338
373 347 311 329 338
Handle Lenght (mm.) 287.07 308.58 344.30 325.47 316.80
Handle Lenght (mm.)
Handle bending calculations:
𝜏 =𝑇 𝑥
𝑑𝑐2
𝐽
𝜏 =107078 𝑁.𝑚𝑚 𝑥
26𝑚𝑚2
𝜋32
𝑥 26𝑚𝑚 4
𝐽𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 =𝜋
32 𝑥 𝑑𝑐 4
𝜏 = 31.03 𝑁/𝑚𝑚2
𝜎𝑏 = 𝑀𝑏 𝑥
𝑑𝑐2
𝐼
𝜎𝑏 = 131370 𝑁.𝑚𝑚 𝑥
26𝑚𝑚2
𝜋64
𝑥 26𝑚𝑚 4
𝐼𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 = 𝜋
64 𝑥 𝑑𝑐 4
𝑀𝑏 = 453 𝑁 𝑥 290𝑚𝑚 𝑀𝑏 = 131370 𝑁.𝑚𝑚
𝜎𝑏 = 76.13 𝑁/𝑚𝑚2
𝜏𝑚𝑎𝑥 = 𝜎𝑏2
2
+ 𝜏2
𝜏𝑚𝑎𝑥 = 76.13
2
2
+ 31.032 𝑁/𝑚𝑚2
𝜏𝑚𝑎𝑥 = 49.11 𝑁/𝑚𝑚2
𝜏𝑦 = 𝜎𝑦
2
𝜏𝑦 =500
2 𝑁/𝑚𝑚2
𝜏𝑦 = 250 𝑁/𝑚𝑚2
𝑓𝑠 = 𝜏𝑦
𝜏𝑚𝑎𝑥
𝑓𝑠 = 250 𝑁/𝑚𝑚2
49.11 𝑁/𝑚𝑚2
𝑓𝑠 = 5.1
The calculations shown above demonstrate that the main screw will not fail for bending.
Figure 13. 1
Power Grip
Table 16. 1
Average British Male Hand Sizes
16. Handle Design Ergonomics 16.1. Ergonomics Background
Handles are the parts an operator will come in contact with most often, therefore it is imperative they are designed
ergonomically without jeopardising the safety factor. Undersized handles could cause danger to operator during use.
Oversized handles could make the screw jack un-ergonomic.
16.2. Grip Background
There are two types of grip, the Power Grip and the Precision Grip. The Power Grip uses the muscles of the hand and
forearm effectively, reduces stress during use. The handle is designed to be held in a power grip which requires the
operator to align the fingers so they work in conjunction with each other. A slightly rough surface will be used to
achieve an anti-slip coating to create sufficient friction preventing slip. The grip is designed for bare hand operation,
contoured to the curve of the palm.
16.3. Hand Sizes
i Fitting The Human, Karl H E Kroemer, Sixth Edition (2008)
Hand measures Population Mean SD (Standard deviation)
Length British 180 10
Breadth at Knuckles
British 85 5
Maximal breadth British 105 5
Circumference at knuckles
British nda ndai
1 Fitting The Human, Karl H E Kroemer, Sixth Edition (2008)
Figure 16. 2
Illustration of Hand Measurement
Table 16. 2
Refined Hand Size Data
#
Mean hand width (mm) 85
Standard deviation of hand width(mm) 5
5th percentile hand width (mm) 76.75
Mean Vertical Length(mm) 180
Standard Deviation of vertical length(mm) 10
5th percentile Vertical length (mm ) 163.5
16.4. Ergonomic Grip Choice
The grip selected is a standard grip made from textured rubber. It provides good grip and reduces required effort for
effective use. The chosen cylindrical shape will generate low wrist deviation ensuring arm and wrist postures are not
affected. The grip will be placed on the cylindrical handle bars. The recommended size is 40 mm but in order to fit all
sizes, we have chosen 45 mm.
5th percentile Calculation
µ - mean
σ – standard deviation
5p = µ- 1.65 x σ
17. Conclusion
This project was to design a manual Screw Jack that can lift a load of 19kN 0.3 metres. We had to encompass
mechanical engineering design knowledge in order to successfully design a working screw jack that can be
manufactured and mass produced. The design was constrained by the specifications as well as manufacturability,
human factors and any other characteristics we chose to encompass.
We looked at many designs and developed our own initial concepts. This was a more difficult process than we had
initially envisaged as choosing original and working designs was complicated due to the options available. This was
complicated further by the calculations and material standards that would determine dimensions of each part. These
constraints helped us understand the complications associated with designing a mechanical devices. The design also
had to consider human factors that would affect its construction, appearance and operation. This project turned up
many complications at every stage while designing the Jack. These were such things as struggling to find suitable
materials to use for each part, to finding a method of keeping the first (Distance) Screw from rotating while the nut is
turned. The biggest challenge was the battle against time. We discovered late in the time scale that we had issues
with parts of our designs and given more time we would have been able to rectify them properly to produce a better
screw jack. The keyed insert for the housing to prevent the distance screw from rotating will be very difficult to
manufacture to tolerance. We have realised that there are other methods of doing this such as inserting keyed
channels as a separate part and even other designs. We also realised that the contact plate could have been better
designed. Given the chance, we would have redesigned it to be manufactured from a hardened plastic or a carbon
fibre compound to reduce weight and material cost. The main complication with our design was the use or a rotating
stationary nut as this restricted how we attached the handles. If we redesigned to incorporate removable handles,
our design would be greatly improved in both ergonomic design and efficiency of use and manufacture. We had
more designs that we wanted to encompass to improve the design efficiency and effectiveness but we could not due
to time. We know this project is only to design but it would be interesting to see our Screw Jack manufactured into a
working model.
Undertaking this project with only academic experience is a daunting task. Having some industrial experience such as
Richard’s experience in the Royal Navy and Adriano’s experience in aeronautics was a great help. This helped with
understanding of the uses, application and the manufacture of parts.
Overall we found this project enjoyable due to its ability to make us think as well as providing an engineering based
challenge. We also found this to be a useful project as we have all gained valuable engineering knowledge that will
prove very useful later in our careers. We believe that this project is currently complete to the best of our current
abilities as our Screw Jack can lift and support loads of 19kN (to a safety factor of 3) in excess of 0.3 metres in a
simple manner, it can overcome any friction caused by the load and incorporates a method of raising small distances
with increased accuracy if needed. As we gain more experience in engineering, we will be able to improve on our
methods and current levels of designs.