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Plastic injection molding tolerance standards

Establishing tolerance with respect to product has significance importance on moldability and cost. It is recommended to indicate only critical dimensions with tolerances on a drawing. Depending on application, a division into three tolerance class can be made:

Normal, Medium & Fine

Cost of manufacture for Medium Tolerance part  will be 1.7 times Normal toleranced part and it will be 3 times for Fine toleranced part.

General molding tolerances are shown below

Drawing code

Dimension (inch)

ABS

AcetaI

Acrylic

Commercial

Fine

Commercial

Fine

Commercial

Fine

A= Diameter*

To 1.000

0.005

0.003

0.006

0.004

0.005

0.003

B=Depth** C=Height**

1.000 – 2.000

0.006

0.004

0.008

0.005

0.006

0.004

2.000 – 3.000

0.008

0.005

0.009

0.006

0.007

0.005

3.000 – 4.000

0.009

0.006

0.011

0.007

0.008

0.006

4.000 – 5.000

0.011

0.007

0.013

0.008

0.009

0.007

5.000 -6.000

0.012

0.008

0.014

0.009

0.011

0.008

6.000 – 12.000

0.003

0.002

0.004

0.002

0.003

0.002

D=Bottom Wall

0.004

0.002

0.004

0.002

0.003

0.003

E=Side Wall

0.003

0.002

0.004

0.002

0.005

0.003

F=Hole Diameter*

0.000 – 0.125

0.002

0.001

0.002

0.001

0.003

0.001

0.125 – 0.250

0.002

0.001

0.003

0.002

0.003

0.002

0.250 – 0.500

0.003

0.002

0.004

0.002

0.004

0.002

0.500 and over

0.004

0.002

0.006

0.003

0.005

0.003

G=Hole Depth

0.000 – 0.250

0.003

0.002

0.004

0.002

0.004

0.002

0.250 – 0500

0.004

0.002

0.005

0.003

0.004

0.002

0.500 -1.000

0.005

0.003

0.006

0.004

0.006

0.003

Flatness

0.000 – 3.000

0.015

0.010

0.011

0.006

0.010

0.007

3.000 -6.000

0.030

0.020

0.020

0.010

0.015

0.010

Concentricity

TIR

0.009

0.005

0.010

0.006

0.010

0.006

Drawing code

Dimension (inch)

Nylon

Polycarbonate

Polyethylene,HD

Commercial

Fine

Commercial

Fine

Commercial

Fine

A= Diameter*

To 1.000

0.004

0.002

0.004

0.003

0.008

0.006

B=Depth** C=Height**

1.000 – 2.000

0.006

0.003

0.005

0.003

0.010

0.008

2.000 – 3.000

0.007

0.005

0.006

0.004

0.013

0.011

3.000 – 4.000

0.009

0.006

0.007

0.005

0.015

0.013

4.000 – 5.000

0.010

0.007

0.008

0.005

0.018

0.016

5.000 -6.000

0.012

0.008

0.009

0.006

0.020

0.018

6.000 – 12.000

0.003

0.002

0.003

0.015

0.006

0.003

D=Bottom Wall

0.004

0.003

0.003

0.002

0.006

0.004

E=Side Wall

0.005

0.003

0.003

0.002

0.008

0.004

F=Hole Diameter*

0.000 – 0.125

0.002

0.001

0.002

0.001

0.003

0.002

0.125 – 0.250

0.003

0.002

0.002

0.015

0.005

0.003

0.250 – 0.500

0.003

0.002

0.003

0.002

0.006

0.004

0.500 and over

0.005

0.003

0.003

0.002

0.008

0.005

G=Hole Depth

0.000 – 0.250

0.004

0.002

0.002

0.002

0.005

0.003

0.250 – 0500

0.004

0.003

0.003

0.002

0.007

0.004

0.500 -1.000

0.005

0.004

0.004

0.003

0.009

0.006

Flatness

0.000 – 3.000

0.010

0.004

0.005

0.003

0.023

0.015

3.000 -6.000

0.015

0.007

0.007

0.004

0.037

0.022

Concentricity

TIR

0.010

0.006

0.005

0.003

0.027

0.010

Drawing code

Dimension (inch)

Polyethylene,LD

Polypropylene

polystyrene

Commercial

Fine

Commercial

Fine

Commercial

Fine

A= Diameter*

To 1.000

0.007

0.004

0.007

0.004

0.004

0.003

B=Depth** C=Height**

1.000 – 2.000

0.010

0.008

0.009

0.005

0.005

0.003

2.000 – 3.000

0.012

0.008

0.011

0.007

0.007

0.004

3.000 – 4.000

0.015

0.010

0.013

0.008

0.008

0.005

4.000 – 5.000

0.017

0.011

0.015

0.009

0.010

0.006

5.000 -6.000

0.020

0.013

0.018

0.011

0.011

0.007

6.000 – 12.000

0.005

0.004

0.005

0.003

0.004

0.002

D=Bottom Wall

0.050

0.004

0.006

0.003

0.006

0.003

E=Side Wall

0.005

0.004

0.006

0.003

0.007

0.004

F=Hole Diameter*

0.000 – 0.125

0.003

0.002

0.003

0.002

0.002

0.001

0.125 – 0.250

0.004

0.003

0.004

0.003

0.002

0.001

0.250 – 0.500

0.005

0.004

0.005

0.004

0.002

0.002

0.500 and over

0.006

0.005

0.008

0.006

0.004

0.002

G=Hole Depth

0.000 – 0.250

0.003

0.003

0.005

0.003

0.004

0.002

0.250 – 0500

0.004

0.004

0.006

0.004

0.004

0.002

0.500 -1.000

0.006

0.005

0.009

0.006

0.005

0.003

Flatness

0.000 – 3.000

0.020

0.015

0.021

0.014

0.007

0.004

3.000 -6.000

0.030

0.020

0.035

0.021

0.013

0.005

Concentricity

TIR

0.010

0.008

0.016

0.013

0.010

0.008

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