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CAD LE
VEL 3 ENGINEERING DIPLOMA UNIT 2/3

TASK FOR APPLICATIONS OF COMPUTER
AIDED DESIGN.

LO.1 LO.2 LO.3 LO.4

RUN DATA FROM BLOODHOUNDSSC ON FIRST FULL REHEAT TEST RUN.

The CAD drawing
s

on the BLOODHOUNDSSC website show all the major parts of the car an
d
will be used to isolate any run problems so modifications can be carried out.

The EJ200 fuel tank is held in place by twelve M
20
x125 stainless steel bolts, washers and
nuts giving all round fixing.





Thes
e are used to attach the webs on the tank to brackets fitted to the chassis. The direct
mounting of the tank helps with some stiffness across chassis rails.


Scenario 1.

The car is run for several passes on a UK runway to test the systems are working corre
ctly
when the EJ200 run at relatively low speeds. The car is taken back to the workshop for an
appraisal and check of the effects of the runs. The team find that 10 of the 12 fixing bolts
for the tank have significantly loosened. They were correctly tight
ened during the assembly
process.
The tank support brackets are found to be unsuitable and a new design will be
needed.
A decision
also
had to be made about the type
o
f fastening used to hold the tank in
place before the car went for faster runs.









The

bracket design showed below has proved to have insufficient stiffness as the three
sided rails flex in action thus loosening the fastenings.






TANK SUPPORTS

SIDE RAIL

300mm

100mm
SQUARE

20X100X80 MILD
STEEL PLATE WITH
M22X125 PLAIN HOLE
INSERTED IN SIDE RAIL




TASK
S

Research the type of fixings that could be used to hold the tank in place in all
condition
s. Choose a suitable fastener. You must make a case for your choice with
an accurate specification. There are some types below to get you started:
-



Change to studs



Use spring washers



Use interior shake
-
proof washers



Use nyloc nuts


Create a 3D CAD drawing of
all parts of
your fixing to show why it will be secure.

Your
drawing should show full

detail

and be rendered.

Engineers work in teams in the BLOODHOUNDSSC project. Threads and

bolt sizes are
notoriously unreliable in CAD software as many of the drawings were created in
Imperial in the US and then converted in Europe. The dimensions are averaged by
the conversion software and can be out by significant factors in pitch and diamet
ers.
To ensure you are able to work accurately work in teams of 3 and create a library of
hex bolts and nuts from 3
-

10mmx 125 that you can share. You may work off your
20mm drawing.


Cap headed HT bolts are often used with Torx or Spline drives on high pe
rformance
vehicles. Draw 3 bolts of your choice, size, thread type and thread length with a cap
head and suitable drive socket.

Redesign the bracket to give a solid fixing with adjustment capability. Draw your


design in a 3D CAD package to demonstrate how
you have solved the problem.


SUGGESTED

ANSWER



The Nordlock Washer System

has a pair of washers with an interlocking step on one side and a
milled upper surface.




The thread pitch

is less than the gradient of the two piece washer making it very unli
kely to work


loose.






The Aerotight nut

has a slotted ridge that is 0.2mm smaller than the thread diameter below it. When
the nut is tightened the slotted ridge is forced out gripping the bolt thread very tightly. The larger
the thread diameter

, the more effective the grip.














Thread Size Nom.

Pitch
mm

A/F Dia. Max
mm

N Dia. Max
mm

H Max
mm

F Min.
mm

M 2.5

0.45

5.0

4.75

2.97

1.49

M 3

0.5

5.5

5.25

3.52

1.89

M 3.5

0.65

7.0

6.65

4.79

2.69

M 4

0.7

7.0

6.65

4.79

2.69

M 5

0.8

8.0

7.65

6.02

3.49

M 6

1.0

10.0

9.58

7.95

4.63

M 8

1.25

13.0

12.53

10.00

6.12

M 10

1.5

17.0

16.53

12.03

7.62

M 12

1.75

19.0

18.47

14.48

9.62

M 16

2.0

24.0

23.47

18.75

12.62



M 20

2.5

30.0

29.47

22.35

15.62



A 3D PRINTED BRACKET DESIGN SOLUTION FROM A CAD PRO
GRAMME AT 0.6 SCALE





Gerry Heather


November 2010


20MM FIXING HOLES

10MM FIXING SLOTS

20MM STEEL WEB
AND FIXING PLATES