https://www.avient.com/sites/default/files/2020-10/2020-gravi-tech-design-guide-.pdf
The wall thickness (W)
for ribs and bosses should be 75% of the nominal
wall ( .75W) .
The outside round should be the inside radius
plus wall thickness (IR + W) .
Unfortunately, this method
only has limited durability and has a minimum
amount of assembly repeatability .2
FIGURE 19 - Mechanical Fasteners
Design Guidlines
Potential high stress
due to wedging action
of screw head
Potential high stress
due to wedging action
of screw head
Poor DesignsPoor Designs Preferred DesignsPreferred Designs
Planned gap between added
bosses prevents excessive
bending of hosing as bosses
touch and go into compression
Planned gap between added
bosses prevents excessive
bending of hosing as bosses
touch and go into compression
Alternative recessed head
design avoids potentially
dangerous wedging action
Alternative recessed head
design avoids potentially
dangerous wedging action
Truss or Round Head ScrewTruss or Round Head Screw
Potential high bending
stress as bolt is tightened
Potential high bending
stress as bolt is tightened
Flat-head Screw
Standard Screw
Plastic Part
Metal Sub-frame
Shoulder Screw
Plastic
Part
Metal
Casting
FIGURE 20 - Mechanical fasteners design guidelines
F=
π × µ × DShaft 1engage × σH
W
I = D – 0.373 = 0.0002"
σH =
1 × W
DShaft
W + v
E( )
σH = = 200psi
0.002 × 1.998
0.375 1.998 + 0.4
450000( )
W = = 1.998
1 – 0.375
0.650( )
2
1 + 0.375
0.650( )
2
W = DShaft
ODHub
1 – ( )2
DShaft
ODHub
( )21 +
FIGURE 16 - Interference fit variable
F=
π × µ × DShaft 1engage × σH
W
I = D – 0.373 = 0.0002"
σH =
1 × W
DShaft
W + v
E( )
σH = = 200psi
0.002 × 1.998
0.375 1.998 + 0.4
450000( )
W = = 1.998
1 – 0.375
0.650( )
2
1 + 0.375
0.650( )
2
W = DShaft
ODHub
1 – ( )2
DShaft
ODHub
( )21 +
FIGURE 17 - Geometry factor variable
F=
π × µ × DShaft 1engage × σH
W
I = D – 0.373 = 0.0002"
σH =
1 × W
DShaft
W + v
E( )
σH = = 200psi
0.002 × 1.998
0.375 1.998 + 0.4
450000( )
W = = 1.998
1 – 0.375
0.650( )
2
1 + 0.375
0.650( )
2
W = DShaft
ODHub
1 – ( )2
DShaft
ODHub
( )21 +
FIGURE 18 - Hoop stress equation
F=
π × µ × DShaft 1engage × σH
W
I = D – 0.373 = 0.0002"
σH =
1 × W
DShaft
W + v
E( )
σH = = 200psi
0.002 × 1.998
0.375 1.998 + 0.4
450000( )
W = = 1.998
1 – 0.375
0.650( )
2
1 + 0.375
0.650( )
2
W = DShaft
ODHub
1 – ( )2
DShaft
ODHub
( )21 +
FIGURE 19 - Press fit pull-out force
.400
.500
.375
.373
.650
FIGURE 15 - Press fit example
Design Guide 13
ADHESIVE TYPES
A chart containing the various specific adhesive
types, with advantages and disadvantages of
both can be seen in the appendix.