LOGO

Machine Design & CAD - II GEAR DESIGN PROJECTMachine Design & CAD - II GEAR DESIGN PROJECT

GROUP MEMBERSKhalil Raza Bhatti 07ME40 GL Waqas Ali Tunio 07ME34 AGLAyaz Ali Soomro 07ME31 Waqar Ahmed Bhutto 07ME36Muhammad Farooque Pirzado 07ME56 Zain-ul-Abdin Qureshi 07ME57

Rack & Pinion Gear Design

MECHANICAL ENGINEERING DEPARTMENT

www.postointernational.tk

Contents

Introduction1

Design Methodology2

Design Consideration3

Design Calculation4

5 Conclusion

Project Objectives:

Understand rack and pinion gear mechanism.

Come up with an innovative solution for building that design as a standard one.

Determine the various forces that are meshed within gears.

In context of all the gear parameters referring to right selection of material for rack and as well as for pinion.

www.postointernational.tk

Need

Need is to develop a system for closing and opening of railway crossing gate with rack and pinion mechanism.

In order to design that we will have to assume some data as shown:

Gate is to slide on a rail by rail and wheel mechanism. Sliding path is frictionless. Two rack and pinion gears are used to slide gate on rail as load

will uniformly be distributed mounted on its ends.

www.postointernational.tk

Rack and Pinion Gear Design

Rack & Pinion Gear

A rack and pinion gears system is composed of two gears. The normal round gear is the pinion gear and the straight or flat gear is the rack. The rack has teeth cut into it and they mesh

with the teeth of the pinion gear. .

Rack

Pinion

Basic Mechanismwww.postointernational.tk

Rack and Pinion Gear Design

Rack & Pinion Gear contd.

Rack and pinion gears provide a greater feedback and steering sensation.

A well designed mechanism such as the rack and pinion gears save effort and time. .

Rack and Pinion Gear Design

Rack & Pinion Gear contd.

Rack and Pinion Gear Design

Designing Rack & Pinion Gear.

.

Engineering Design

Identify a Need

Preliminary Design

Conceptual Design

Final Design

Manufacture

Sales & Delivery

Designing Rack & Pinion Gear.

Rack & Pinion

Straight teethor

Spur Type

Rack & PinionTwo types

Rack and pinion gears are available in two variations

Helical teethor

Helical Type

www.postointernational.tk

Design Requirements

Force

SpeedEffort

Max:Weight

Dimensions

Rack & Pinion

Basic Design Characteristic

www.postointernational.tk

Preliminary Design

For spur gear design, pinion and rack both have straight teeth or spur geometry of teeth.

So for we will first consider the design of pinion as spur gear.

www.postointernational.tk

Spur Gear Design and Selection

Objectives

• Calculate forces on teeth of spur gears, including impact forces associated with velocity and clearances.

• Determine allowable force on gear teeth, including the factors necessary due to angle of involute of tooth shape and materials selected for gears.

• Understand how lubrication can cushion the impact on gearing systems and cool them.

www.postointernational.tk

Specifications for standard Gear Teeth

www.postointernational.tk

Forces on Spur Gear Teeth

Ft = Transmitted forceFn = Normal force.Fr = Resultant forceθ = pressure angleFn = Ft tan θFr = Ft/Cos θ

www.postointernational.tk

Forces on Spur Gear Teeth

Power, P; =

Torque,

Combining the above we can write:

www.postointernational.tk

Surface Speed

Surface speed (Vm) is often referred to as pitch-line speed:

www.postointernational.tk

Strength of Gear Teeth

Lewis form factor methodLewis equation

Fs = Allowable dynamic bending force (lb) Sn = Allowable stress. Use endurance limit and account for the

fillet as the stress concentration factor b = Face width (in.) Y = Lewis form factor (From Table) Pd = Diametral pitch

www.postointernational.tk

Lewis form factors (Y)Table

www.postointernational.tk

Classes of Gears

• Transmitted load depends on the accuracy of the gears

• Gear Manufacture

– Casting

– Machining

• Forming

• Hobbing

• Shaping and Planing

– Forming

www.postointernational.tk

Force Transmitted

Transmitted load depends on the accuracy of the gears.

A dynamic load factor is added to take care of this.

• Ft = Transmitted force

• Fd = Dynamic force

• Commercial

www.postointernational.tk

Classes of Gears

Carefully cut

Precision

Hobbed or shaved

www.postointernational.tk

Expected error in tooth profileswww.postointernational.tk

Design Methods

• Strength of gear tooth should be greater than the dynamic force; Fs ≥ Fd

• You should also include the factor of safety, Nsf.

www.postointernational.tk

Service Factorswww.postointernational.tk

Face width of Gears

Relation between the width of gears and the diametral pitch.

www.postointernational.tk

Dynamic Beam Strength of the Gear

To increase the dynamic beam strength of the gear

– Increase tooth size by decreasing the diametral pitch

– Increase face width upto the pitch diameter of the pinion

– Select material of greater endurance limit

– Machine tooth profiles more precisely

– Use proper lubricant and reduce contamination

www.postointernational.tk

Buckingham Method of Gear Design

• It offers greater flexibility.

• Expected error is based on different-pitch teeth.

• More conservative design.

www.postointernational.tk

Wear strength (Buckingham)

Fw = tooth wear strength.Dp = diametral pitch of pinion.Dg = diametral pitch of gear.b = face width.Kg = load stress factor.

www.postointernational.tk

Reference

www.gearmanufacture.comwww.rackandpinion.design.netwww.gearfactory.comwww.mechanicaldesign.comWikipedia searchMachine Design R.S. KhurmiHand book of mechanical engineering.

www.postointernational.tk

Conclusion

So far we have been able to calculate the design of pinion only in the next phase of project we will be designing the rack.

Passed on fundamental knowledge of rack and pinion gear mechanism and it design procedure & finally selecting the right material for it.

www.postointernational.tk

LOGO

www.postointernational.tk

MECHANICAL ENGINEERING DEPARTMENT