SidhantSharma CAD Project03 Report

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PROJECT 03CAD THEORY AND DESIGN

UB

SIDHANT SHARMA#36819679MAE -577

09/27/2010



Contents

1 Introduction…………………………….…………3

2 Problem statement…………………..……….……3

3 Result……………………………………….……..4

3.1

Cube transformations using MATLAB GUI..………………..4

3.2Bezier curve plots using MATLAB GUI..……………………6

3.3Modeling and assembly in SolidWorks 2010..………………10

4 Design of pulley system..………………………....18

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5 Tolerance calculation…………………………..….22

6 Conclusion…………………………………….…..25

7 References………………………………...……….26

1 Introduction

This project is intended towards basic CAD implementation and drawing using the GUI feature

in MATLAB and also to explore the techniques of 3-D modeling, design and assembly in

SolidWorks 2010 software package.

The GUI feature in MATLAB uses various interactive features like push buttons, drop-down

menus, text boxes, axes to interact with the user, receive input commands and data in order to

produce the required graphical results. We have used GUI’s for studying the 3-D transformation

matrices for translation, rotation and applied these operations on a cubic object to move or rotate

it as desired. We have also used the theory of bezier curves to obtain linear, quadratic as well as

cubic bezier curves depending on the number of control points enter by the user in the GUI.

These interactions with the user are through text boxes or mouse clicks.

SolidWorks is one of the most user friendly software package available in the software industry

today. We have not only learnt the basics of modeling in this software through tutorials but also

used the capability of this software to model and assemble the parts of a simple pulley system.

Creating a 2-D drawing from 3-D models is a very useful feature of SolidWorks which has been

used in this project.

In this project, we have also designed the parts of a pulley system based on the load, speed and

the tolerance requirements. As far as possible, standard parts have been used as they are easily

and cheaply available and the overall cost of the pulley system has been accordingly estimated.3



2 Problem statement

We are required to create a MATLAB GUI for plotting a unit cube. This GUI should allow the

user to translate the unit cube to a certain co-ordinate position (x, y, z) which is specified by the

user. It should also be possible to rotate the cube about its own x, y and z-axis according to the

angle specified in the interface.

The second MATLAB GUI must give the user the ability to enter control points in order to make

2-D and 3-D linear, quadratic or cubic bezier curve plots in the plotting window depending on

the choice and number of control points entered.

The third part of the problem requires us to go through the basics of modeling and assembly in

SolidWorks 2010 using the available tutorials. This knowledge has to be then used to model the

parts of a simple pulley system. These parts are to be assembled using the same software. A 2-D

drawing sheet is to be made for the pulley.

The next part of the problem is to design a pulley system based on the model assembled in the

previous part. The pulley can be assumed to be mounted on a larger system and the maximum

load and maximum linear speed requirements are 10kg, 5m/s respectively. The design should

include standard bolts, pulley, L-brackets, bush bearings and washers. The cost of the entire

system has to be estimated.

Tolerances on holes in the base plate, L-bracket are to be estimated to find the maximum,

minimum tolerance on the placement of the L-bracket on the base plate which results in

misalignment. What modifications can be done in the design of the L-bracket in order to

minimize misalignment of the pulley? Study and give reasons regarding the importance of using

the same reference when dimensions holes on the base plate.

3 Result

A MATLAB GUI is created by using the guide command in the MATLAB command window.

All the features i.e push buttons, axes or drop-down menus are added to the GUI and saved. This

creates a figure file as well an associated m-file that can be used for programming the inteface.

GUI’s were created for the cube transformation as well as the Bezier curve problem.

After going through the Getting Started tutorial in Solidworks, the acquired basics were used to

model various parts of a simple pulley system and assemble them. Using this assembly, the next

step was to design a pulley system for load, speed, cost and geometric tolerance requirements.

4







Figure 3 MATLAB GUI for plotting 2-D Bezier curves

Figure 4(a) shows a 2-D linear Bezier curve created by selecting linear from menu,

followed by two left clicks inside the axis and plot button while figure 4(b) shows a

2-D quadratic Bezier curve obtained by three left clicks followed by the plot button.

On the other hand, figure 4(c) shows a 2-D cubic Bezier curve obtained by four left

clicks inside the axis, and the plot push button.

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(b)

(a) (c)Figure 4 (a) 2-D linear Bezier curve; (b) 2-D quadratic Bezier curve and ; (c) 2-D cubicBezier curve drawn by left mouse clicks

Figure 5 shows the GUI created for the 3-D bezier curve problem. It has an axes

object for plotting the curves. There are two push buttons, one for plotting and the

other for clearing the previous plots. The type of 3-D Bezier curve to be plotted canbe selected from the drop down menu which has the options for a linear, quadratic

and cubic type.

The control points can be specified by the user in the text boxes provided. 2 points

have to be entered for the linear type, 3 for the quadratic and 4 for the cubic type

after the type of curve has been selected from the drop down menu. There are

three text boxes (x,y,z) for defining a control point in 3-D space.

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Figure 5 MATLAB GUI for plotting 3-D Bezier curves

Figure 6(a) shows a 3-D linear Bezier curve created by selecting linear from the

menu followed by entering two control points in the text boxes and the plot button

while figure 6(b) shows a 3-D quadratic Bezier curve obtained by entering three

control points.

On the other hand, figure 6(c) shows a 3-D cubic Bezier curve obtained by four

entering four control points and the plot push button. These points are entered in

figure 5.

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Fig 7 shows the part modeled in the first lesson while figure 8 shows the assembly made in the

second lesson.

Figure 9 shows the third lesson on how to make 2-D drawing from parts

Figure 7 part made for lesson 1Figure 8 assembly for lesson 2

Figure 9 drawing for lesson 3

The first part modeled for the pulley assembly is the baseplate. It has four threaded holes and a

slot as shown in figure 10.

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(a) (b)

Figure 11 (a) L-bracket model created in solidworks 2010 and (b) another view of L-bracket

The next part modeled was the M10X 1.5 pitch hexagonal head bolt shown in figure 12.

Figure 12 hexagonal headed bolt created in solidworks 2010

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Figure 13 (a) and (b) show two views of the pulley. It was created using the revolve sweep

feature in solidworks once the cross section was sketched in the sketch mode. Keyway was

added to the model after the sweep.

(a) (b)

Figure 13 (a) pulley modeled in solidworks 2010 ; and (b) another view of pulley

Figure 14 (a) shows the key that fits in the pulley and axle keyways whereas figure 14 (b) shows

the washer to be used.

(a) (b)Figure 14 (a) key ; and (b) washer

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Figure 15 (a) shows the pulley axle which has a keyway machined inside and figure 15 (b) shows

the bush bearing that is fitted into the top hole in the L-bracket.

(a) (b)

Figure 15 (a) pulley axle modeled in solidworks 2010 ; and (b) bush bearing

Figure 16 shows the subassembly consisting of pulley, axle, key and washer. This subassembly

is mounted in between the L-plates in the second stage of the assembly

Figure 17 and figure 18 shows two views of the entire pulley assembly after all the parts are

assembled. The L-brackets are screwed on to the base plate using the bolts. Then the bushes are

fit into the L-plates. Key is inserted between pulley and pulley axle. The pulley and pulley-axle

sub-assembly including washer is then mounted between the L-plates to complete the assembly

as shown.

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Figure 16 pulley and axle subassembly

Figure 17 pulley system assembly

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Figure 18 another view of pulley system assembly

Figure 19 shows an exploded view of the entire assembly using the explode view feature in

SolidWorks 2010.

Figure 19 exploded view of pulley assembly

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Figure 20 shows a 2-D drawing sheet for the pulley created from the 3-D model of the pulley.

The sectional and detailed views are labeled and shown.

Figure 20 2-D drawing sheet for pulley

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4 Design of pulley system

The task assigned in the problem is to design a pulley system to meet the maximum load

requirement of 10kg and a maximum linear speed of 5m/s.

Considering a factor of safety, FOS = 1.5, the power requirement of the pulley can be calculated

using the relation

Power = Force X velocity = 10 x 1.5 x 9.81 x 5

= 735.75 W = 0.735 KW ( approx. 1 HP)

Therefore the HP requirement is 1 HP, from table 1 below, the size of the pulley can be

determined that meets the power and speed requirements.

Table 1: Standard pulley size (handbook for machine designers and draftsman by Halsey)

Therefore the pulley that we selected for the purpose has an outer diameter of 4 inches, while

other specifications are given below in figure 21.

The cost of the pulley is $ 8.00.

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Figure 21 standard idler V-pulley model withspecifications

The standard bolt size that we use in the design is M10 with a pitch of 1.5 mm. Four bolts are

required and the holes have to be accordingly drilled in the baseplate and L-brackets. The

standard bolt specifications are given below in figure 22.

The cost of these bolts is $ 8.00 for a pack of 10. Therefore the cost of 4 bolts is $ 3.00

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Figure 22 standard hex bolt model with specifications

Since the bore diameter of the selected pulley is ½ inch, the pulley axle which mates inside the

bore required is also modified to have a spindle diameter of ½ inch and a length of 3 inches. The

pulley axle is shown in figure 15 (a).

The cost for the pulley axle is $ 2.00 (from McMaster Carr products).

The bush bearing required will also have an inner diameter of ½ inch as the axle moves inside it.

The standard bush is shown in figure 23 below.

The cost of two sleeve bearings is $ 2.50.

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Figure 23 standard sleeve bearing model with specifications

The bush bearing required will also have an inner diameter of ½ inch as the axle moves inside it.

The standard bush is shown in figure 23 below.

The cost of two sleeve bearings is $ 2.50.

The standard washer to be used should have an inner diameter of more than ½ inches. The

selected washer is shown in figure 24 below. The cost is $5 for 10 pack i.e 50 cents/unit.

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Figure 24 standard washer model and specifications

Density of steel = 7850 kg/cu. M

Cost of steel = $0.35 / Kg

The cost of the base plate = 300x120x20x10e-9x7850x0.35 = $ 2.00

The cost of two L-brackets = 2 x $1.2 = $ 2.40

The cost of key = $ 0.10

Total cost of pulley assembly can be estimated as = 8 + 3 + 2 + 2.5 + 2.5 + 2 + 2.4 + 0.60

= $ 23

5 Tolerance calculation

The tolerance on the mounting holes of base plate and L-bracket is shown in figure 25(a) and (b).

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(a) (b)Figure 25 (a) tolerances on holes on base plate (b) tolerances on holes on L-bracket

For tolerance calculation, both the L-plates are considered to be mounted on the base-plate and

therefore the dimensional error in the concentricity of the top holes of the two L-plates will result

in the misalignment of the pulley. The maximum and minimum error in the concentricities iscalculated accordingly which gives the relative misalignment of the plates with respect to each

other.

The maximum tolerance of alignment of the L-plates on the base plate =

2*tolerance of baseplate hole + 2*tolerance on L-bracket hole =

2*0.05 + 2*0.02 = 0.14 mm

The minimum tolerance of alignment of the L-plates on the base plate =

tolerance of hole on L-bracket

= 0.02 mm

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In order to reduce the misalignment of the L-brackets on the base plate, the design of the L-

brackets can be modified to the one shown below in figure 26. As seen below that instead of

using two machined L-brackets we are using a single cast bracket which effectively has two L-

brackets joined together.

Therefore we use only two mounting holes instead of using four in the earlier case of two brackets. This will not only reduce horizontal misalignment as the two holes can be referenced

from a single face leading to no tolerance stacking. Even if there is slight misalignment, the

pulley would be mounted properly as the top holes in the bracket are concentric and the pulley

can be mounted in proper alignment between it.

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Figure 26 modified L-bracket to reduce pulley misalignment

Importance of referencing from a single face: The holes must be referenced from a single face

because it leads to more accuracy in the position of the holes. If the holes are referenced from

different references it leads to addition of tolerances or tolerance stacking, therefore leading to

dimensional errors as shown in figure 27. If one hole is positioned inaccurately, it will lead to a

further misplacement if the same hole is used as a reference.

However, using the same surface for dimensioning all the holes will make their placement

independent of each other. The single reference gives a max error of 0.5 mm whereas in the other

case the error can go upto 1mm as shown.

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Figure 27 tolerance stacking example

6 Conclusion

This project has made us aware of the capabilities of MATLAB GUI’s for implementing CAD

for both 2-D and 3-D cases. The user can effectively program the GUI in order to produce the

desired plots.

SolidWorks 2010 has been used to do the modeling and assembly of the pulley system. It is a

very user friendly software and it is fairly easy to make assemblies and sub-assemblies of parts

or make sectional drawing of parts modeled.

7 References

BOOKS

[1] Handbook for machine designers and drafters by Halsey

WEBSITES

[1] www.McMaster.com

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SidhantSharma CAD Project03 Report