Plastic Boss Design Guidlines

Plastic Boss Design Guide LinesGeneral Rules

Thread Flank Angle:    
Thinner flank angles on threads (30 degree vs. 48 degree) reduce radial stress on plastic boss and helps to resist strippage 

Length of Engagement: 
Fasteners should have a minimum of 2.5 times the fastener diameter for length of engagement into the plastic boss.  Shorter length engagement will have lower strip out torque and less clamp load

Draft Angle:
The Boss ID design should have a ½ to 2 degree included draft angle, (+/- ½ degree tolerance is typical) with a lead in similar to the diagram.

Nominal Boss ID:
Calculated at a depth equal to half of the fastener's total length of engagement;  In moderately stiff materials, you should start with a hole size that is 75% to 80% thread engagement. 

Driver Gun speed
The assembly driver gun should not exceed 600 rpm

Seating and Assembly Torque:
Developed through testing.  Assembly torque is normally 70% of the average failure torque.

Mechanical properties of selected plastics based on ASTM D 4000 or ISO 1043

Material

Tensile
Strength

Tensile
Modulus

Flexural
Strength

Impact
Strength

Hardness
Rockwell

Flame
rating
UL94

MPa

ksi

GPa

106 psi

MPA

ksi

J/m

ft*lb/in.

ABS

41

6.0

2.3

0.33

72.4

10.5

347

6.5

R103

HB

ABS-PC

59

8.5

2.6

0.38

89.6

13.0

560

10.5

R117

HB

DAP

48

7.0

10.3

1.50

117

17.0

37

0.7

E80

HB

POM

69.0

10.0

3.2

.47

98.6

14.3

133

2.5

R120

HB

PMMA

72.4

10.5

3.0

.43

110

16.0

21

0.4

M68

HB

PAR

68

9.9

2.1

0.30

82.7

12.0

288

5.4

R122

HB

LCP

110

16.0

11.0

1.60

124

18.0

101

1.9

R80

V0

MF

52

7.5

9.65

1.40

93.1

13.5

16

0.3

M120

V0

Nylon 6

81.4

11.8

2.76

0.40

113

16.4

59

1.1

R119

V2

Nylon 6/6

82.7

12.0

2.83

0.41

110

16.0

53

1.0

R121

V2

Nylon 12

81.4

11.8

2.3

0.34

113

16.4

64

1.2

R122

V2

PAE

121

17.6

8.96

1.30

138

20.0

64

1.2

M85

V0

PBT

52

7.5

2.3

0.34

82.7

12.0

53

1.0

R117

HB

PC

69.0

10.0

2.3

0.34

96.5

14.0

694

13.0

R118

V2

PBT-PC

55

8.0

2.2

0.32

86.2

12.5

800

15.0

R115

HB

PEEK

93.8

13.6

3.5

0.51

110

16.0

59

1.1

---

V0

PEI

105

15.2

3.0

0.43

152

22.0

53

1.0

M109

V0

PES

81.4

12.2

2.6

0.38

129

18.7

75

1.4

M188

V0

PET

159

23.0

8.96

1.30

245

35.5

101

1.9

R120

HB

PF

41

6.0

5.9

0.85

62

9.0

21

0.4

M105

HB

PPO (mod)

54

7.8

2.5

0.36

88.3

12.8

267

5.0

R115

V0

PPS

138

20.0

11.7

1.70

179

26.0

69

1.3

R123

V0

PSU

73.8

10.7

2.5

0.36

106

15.4

64

1.2

M169

HB

SMA

31

4.5

1.9

0.27

55

8.0

133

2.5

R95

HB

UP

41

6.0

5.5

0.80

82.7

12.0

32

0.6

M88

HB

UL: Underwriters Laboratory.

 

Symbols and corresponding names of selected engineering plastics
 


Symbol

Name

ABS

Acrylonitrile-butadiene-styrene

ABS-PC

ABS-polycarbonate

DAP

Diallyl phthalate

POM

Poly-oxy methylene

PMMA

Poly-methyl-methacrylate

PAR

Polyarylate

LCP

Liquid crystal polymer

MF

Methyl floride

PAE

Polyarylether

PBT

Polybutylene trephathalate

PC

Polycarbonate

Symbol

Name

PEEK

Polyetheretherketone

PEI

Polyether-imide

PES

Polyether sulfone

PET

Polyethylene terephthalate

PF

Phenol formaldehyde

PPO

Polypheneylene oxide

PPS

Polypheneylene Sulfide

PSU

Polysulfone

SMA

Styrene-maleic anhydride

UP

Unfilled polyester

 

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Thermoplastics

Ductile

Polyethylene (PE)

150,000

Hi-Low twin lead

Polypropylene (PP)

200,000

Polycarbonate (PC)

340,000

Hi-Low twin lead, Tri-Lobe 48-2
twin lead

ABS, 0-20% glass fill

350,000

Polyamide 66 (PA)

350,000

Acetal (AC)

400,000

Polystyrene (PS)

430,000

Polypheylene, 40% talc fill (PP40)

500,000

Polypheylene Sulfide

550,000

Moderate

ABS, 20% glass fill

650,000

Tri-Lobe 48-2
twin lead

Polyamide 66, 12% glass fill

800,000

Polycarbonate, 20% glass fill (PC20)

850,000

Brittle

Polycarbonate, 30% glass fill (PC30)

1,100,000

Tri-Lobe 48-1
single lead
Tri-lobe 45
single lead

Polybutylkene Terephthalates 30% glass fil (PBT30)

1,100,000

Polyamide 66, 30% glass fill (PA30)

1,200,000

Liquid Crystal Polymer (LCP)

1,400,000

Thermosets

Brittle

Polyphenylene Sulfide, 40% fill (PPS40)

1,700,000

Type 25 Thread
Cutting Screw

Phenolic, 20% glass fill

1,750,000

Polyester, 5-% glass fill

2,100,000