MEC2304 – Solid modelling 1

Assignment 2

Solid modelling project

Due date: 27 October 2014

Value: 750 of the 1000 marks for this course

Background

Figure 1 shows the arrangement of a gear pump. The following design considerations and

modifications are to be implemented.

1. It has been determined that there is a market for a variety of similar pumps but with

reduced pumping capacity. This can be achieved by fitting ‘thinner’ gears. The same

housing can be utilised but with a reduced depth of the machined cavity to suit the

‘thinner’ gears. The current design shows 19 mm wide gears but future designs must

cater for any gear width from 15 mm to 19 mm.

2. The single groove pulley shown is to be replaced by a double-groove pulley. More

information on this pulley and how it is to be attached to the pump shaft is given in item

6 below and later in this document.

3. The ¼” pipe thread is to be replaced by a M12 x 1.5 thread.

4. The gears are to be metric with the following specifications:

number of teeth 13

pitch diameter 32.5 mm

outside diameter 37.5 mm

pressure angle 20O

module 2.5 mm

5. It has also been decided to supply an assembled kit equipped with two gear pumps,

connected in series, driven by an electric motor. The pumps and the motor are to be

mounted on a specially designed and fabricated steel base. The general arrangement is

depicted in Figure 3.

6. Drive from the motor to one of the pumps is by V-belts running between two double-

groove pulleys. Each pulley is keyed to its respective shaft using 4mm keys. (Do not use

the taper pin shown in Figure 1.)

7. The electric motor, refer to Figure 5 for the basic dimensions, runs at a constant 1440 rpm

but the gear pumps need to operate at 900 rpm ± 20 rpm.

8. Two different length drive belts could be used depending on supply availability - 450 mm

and 500 mm pitch lengths. Both belts are classified as type ‘Y’ section.

2 MEC2304 – Solid modelling

9. The second pump is driven by the first through a flexible drive coupling – see Figure 4.

The Project

Your task is to:

1. Create parametric feature-based solid models for all the components of the gear pump as

shown in Figure 1 - but with a suitable double-groove pulley instead of the single-groove

pulley represented.

2. Create an assembled model of a single pump showing all parts in their working positions

and with the 19 mm wide gears fitted.

3. Set up a parametric relationship to automatically update the housing cavity depth and

other parts, features and dimensions affected by the gear width change as mentioned in

item 1 of the Background section (i.e. a simple dimension edit to the width of the driving

gear model should automatically change the sizes and / or shape of the effected mating

parts and features.)

4. Produce a model of a double-groove pulley for the electric motor.

5. Design and model a base to support the motor and two pumps. The base should be

designed to allow positional adjustability of the motor so that the belts can be tensioned

as well as accommodating the different length V-belts - as mentioned in the Background

section, item 8.

6. Create a second assembled model. This time the model should show the spatial

arrangement of the motor, pumps and base. You will need to include the pulleys, coupling

and all other associated drive components e.g. keys, belts, couplings. You should also

show all the fasteners – bolts, nuts, washers, screws etc.

7. Produce two separate engineering assembly drawings - one of the overall assembly as in

6 above and the second of a single pump as in 1 and 2 above. In addition to the

orthographic views the drawing should also include a perspective view, title block, parts

lists, and other information generally associated with assembly drawings.

8. Produce fully dimensioned engineering detail drawings for the parts listed below:

housing

housing cover

gear

gear stud

shaft

mounting base

drive and driven pulleys

Specify appropriate surface finish requirements, general tolerances, and other information

normally shown on a detail drawing. In addition to the orthographic views each drawing

should also include a perspective view of the part.

9. Nominate and justify suitable fits and tolerances, on a separate A4 sheet, for the

following mating parts / features:

MEC2304 – Solid modelling 3

(a) driven gear and gear stud

(b) housing and gear stud

(c) driving gear and shaft

List the basic size and dimension tolerances for each fit on the sheet. The specific

tolerances should also be shown in the detail drawings.

Guidance on the Project

Some of the diagrams provided show limited details and in many cases the dimensioning of

the details is incomplete or missing. Therefore, you will be expected to combine some

research with sound practical judgement to obtain all the missing information necessary to

complete the design.

Before commencing this assignment you should think about the function of each feature and

each part and how the individual components might be made. Also consider the physical

assembly process, i.e. how the parts actually fit together, the order in which the components

might be put together and the use of sub-assemblies. Your model creation process should

reflect this wherever possible. Some guidance is given in the instructions for the Roller

Bracket exercise you completed as part of assignment 1.

Gears

You may simplify the gear tooth profile to that shown in Figure 2. (Normally, the profile of

the tooth face is that of an involute and not of a constant radius arc as shown.)

Keys

There is information regarding keys and keyways in the text by Boundy. You should use the

nominal dimensions given there.

Pulleys and belts

For the V-belts you should use a ‘Y’ section belt.

You will need to determine suitable pitch diameters for both the motor pulley and the pump

pulley to satisfy the requirements in item 7 of the Background section.

For a list of pulley sizes to choose from and for critical pulley, groove and belt dimensions

you should refer to the tables and related information at the end of this document.

Base frame

Use 30 x 30 x 3 mm mild steel angle iron for all elements of the base frame. You may use

Figure 3 as a guide to your design. Angle iron sizes can be found in the Onesteel Hot Rolled

and Structural Steel Products 7th edition catalogue which you should be able to access on the

internet.

Fasteners

Use M6 bolts and nuts for securing the motor and pumps to the base. Use M4 threads for

fixing the pulleys and coupling. There is no need to include the actual thread features on

these fastener models or their mating threads.

Threads

Model the M20 and M12 threads on the Housing and Housing cover as helical sweeps.

Boundy shows the thread form geometry. For the other pump threads use the cosmetic thread

4 MEC2304 – Solid modelling

feature.

Pipes, hoses and their fittings

Do not include these.

What you need to submit:

Your assignment is to be submitted online through USQStudyDesk in a compressed

(zipped) folder. Do not submit the files individually.

In the zipped folder include:

Part ‘.prt’ files and assembly ‘.asm’ files of all the Creo2.0 models*

‘.pdf ‘ files for all the working drawings listed in 7 and 8 of The Project section – i.e. you

will need to ‘save as’ or ’export’ the Creo2.0 drawings (.drw) to .pdf before submitting.

Do not submit Creo2.0 .drw files.

A ‘.pdf’ electronic copy of an A4 sheet or sheets (created from a word document) with:

a listing of the file names you used for each part and each assembly

fits and tolerance justifications as requested in item 9 of The Project section

instructions on how to test the parametric relationship between the Gears and other

components.

Important - check that your files open correctly from the zipped folder before submitting

your assignment. A marks penalty will apply if the files cannot be opened or easily accessed

by the markers.

*If you use a program other than PTC Creo2.0 (or older versions) you will need to

convert the files to Creo2.0 ‘.prt’ and ‘asm’ files. If your software does not support this

conversion then save or export them as IGES or STEP files. Either way you should also

submit all original / native model files e.g. if you use Solid Edge submit the Solid Edge files

as well as the IGES or STEP files. You should also include printouts of the model tree

directories so that you model creation process can be assessed.

Marking this assignment

The following sample marking sheet has been included to indicate the criterion to be assessed

and the relative marking for each criteria.

MEC2304 – Solid modelling 5

MEC2304 Assignment 2 – marking sheet

Semester 2, 2014

Student name:

Marker’s name : Total mark / 750

Models

Criterion Your mark Out of

1. completeness – all parts modelled and all features

included

100

2. accuracy of parts and assembly, functionality and

practicality of the Base, Pulleys and general arrangement

designs

175

3. presentation / creation of computer models, part and / or

assembly relations

175

total

450

Assembly drawing

Criterion Your mark Out of

1. completeness – all parts shown and clearly identified;

title block / parts lists

50

2. presentation / clarity – view selection and layout

50

total

100

Detail drawings

Criterion Your mark Out of

1. completeness – all parts drawn and submitted; title block

/ notes

60

2. presentation / clarity – view selection and layout

60

3. accuracy – dimensioning / tolerances / surfaces finishes

80

total

200

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Figure 1: Gear pump

(Source: Luzadder & Duff 1989, Fundamentals of engineering drawing, 10th edn, Prentice Hall, p. 440.)

MEC2304 – Solid modelling 7

Figure 2: Gear tooth profile

Figure 3: General arrangement

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Figure 4: Flexible coupling parts

MEC2304 – Solid modelling 9

Figure 5: Electric motor – basic dimensions

V-belts and V-groove pulleys

The follow information relates to the sizes and dimensions associated with V-belts and V-

groove pulleys.

To calculate the centre distance between the pulleys:

C = A + ( ) where

( )

and

( )

C = centre distance

D = pitch diameter of larger pulley

d = pitch diameter of smaller pulley

L = pitch length of belt

(SAA HB61999)

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(SAA HB61999)

(SAA HB61999)

MEC2304 – Solid modelling 11

(SAA HB61999)

Reference

SAA HB61999, Design standards for mechanical engineering students, 4th edn, Standards

Australia,