Screw Jack Report

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


Wide choice of load capacity and Screw lengths


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


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


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


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


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


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°


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


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


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


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


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


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


Dome Nut

Zinc plated steel


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


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


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.


𝜋 𝑥 𝑑𝑚 𝑙 = 𝑃

tan 𝜆 = 5𝑚𝑚

𝜋 𝑥 22𝑚𝑚 tan 𝜆 = 0.07 𝜆 = 4. .140

𝛼 = 3⁰


𝛼𝑛 = 2.990

- Self-Locking demonstration:


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



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


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.


𝜋 𝑥 𝑑𝑚 𝑙 = 2𝑃

tan 𝜆 = 2(8𝑚𝑚 )

𝜋 𝑥 39.668𝑚𝑚 tan 𝜆 = 0.13 𝜆 = 7.320

𝛼 = 3⁰


𝛼𝑛 = 2.980

- Self-Blocking demonstration:


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


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


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


32 𝑥 (𝑑𝑜𝑢𝑡𝑒𝑟

4 − 𝑑𝑖𝑛𝑛𝑒𝑟4)


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


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.



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


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



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


32 𝑥 𝑑𝑐 4


𝑑𝑐2

𝐼

𝜎𝑏 = 56625 𝑁.𝑚𝑚 𝑥

18𝑚𝑚2

𝜋64 𝑥 18𝑚𝑚 4

𝜎𝑏 = 98.9 𝑁/𝑚𝑚2


64 𝑥 𝑑𝑐 4

𝑀𝑏 = 453 𝑁 𝑥 125𝑚𝑚 𝑀𝑏 = 56625 𝑁.𝑚𝑚


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


32 𝑥 𝑑𝑐 4

𝜏 = 31.03 𝑁/𝑚𝑚2


𝑑𝑐2

𝐼

𝜎𝑏 = 131370 𝑁.𝑚𝑚 𝑥

26𝑚𝑚2

𝜋64

𝑥 26𝑚𝑚 4


64 𝑥 𝑑𝑐 4

𝑀𝑏 = 453 𝑁 𝑥 290𝑚𝑚 𝑀𝑏 = 131370 𝑁.𝑚𝑚

𝜎𝑏 = 76.13 𝑁/𝑚𝑚2


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.

Screw Jack Report

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Transcript of Screw Jack Report