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ASSIGNMENT

GEARBOX DESIGNFAQs

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ABOUT THIS DOCUMENT

The purpose of this document is to share the

commonly asked questions.

It does not add, delete or modify any of thespecifications / requirements.

The assignment specifications and requirements

remain the same, as outlined in the originalassignment description document.

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MODULE SELECTION

What module do I use to transfer the requiredamount of torque?

Selecting an exact module requires analysing several factors, such as

gear material, torque/power, gear-tooth bending & wear, surface

durability.

Such analysis is beyond the scope of this assignment.

Any module based on your best judgment will be acceptable.

To get some idea of the required module, inspect the torque carrying

capacity of gears. Some manufacturers (e.g. khk) do provide the torque

carrying capacity of their gears.

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GEAR SIZE

What if my worked-out gears are not

available in the gear catalogues?

Take the required information from the closest available size.

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BENDING MOMENTWhat value of the Bending Moment do I use in the

formula for shaft diameter?

Determine the resultant value by considering the bending moment

diagrams for vertical and horizontal forces.

(Refer to the power point presentation on procedure for design of ashaft)

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STRESS CONCENTRATIONS

How do I decide the stress concentration factors?

It depends on the shaft geometry and loading:

In case of uniform torque, stress concentration is neglected when considering the torsional shear

However, the bending moment is fully reversed. Therefore, the stress concentration should beconsidered.

Initially, these values are selected based on engineering judgment. Consider factors like shaft

shoulders, retaining ring grooves etc.

Verify your assumptions once the shaft dimensions are known.

For this assignment, the stress concentration factors can be ignored.

However, stress relieving strategies need to be discussed in the relevant sections of your

report.

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FATIGUE LIFE FACTORS

How do I decide the fatigue life factors?

These factors depend on the properties (e.g. surface finish,reliability etc) of your selected shaft and shaft material.

Proper selection of these factors requires knowledge of fatigue

failure, which is discussed in Materials 337 unit.

Your best judgment will be acceptable.

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What if the calculated shaft diameter is larger than

the bore size of my selected gears?

Try stronger material for the shaft.

SHAFT DIAMETER

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SHAFT DIAMETER & BEARING BORE SIZEWhat if the bearing bore size is larger than

the shaft diameter?

There are several ways to overcome this problem.

Radial contact ball bearings

Angular contact ball bearings

Radial contact roller bearings

Angular contact roller bearings

Needle roller bearings

Multi-row ball bearings

Within each of these

categories, try X-light, light,

and medium duty bearings.