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A Guide to The Design

Tolerances on Machined Plastic Components

Plastics are subject to different physical laws than metals.

 

The up to 10-fold greater thermal expansion, the volume change due to moisture absorption and subsequent dimensional changes due to the reduction of residual stresses in the long-term behaviour preclude the guarantee of narrow dimensional tolerances. For these reasons, plastic components should be tolerated differently.

As a rule, the function of the plastic part is guaranteed for the tolerance classes specified under DIN / ISO 2768. If any narrower tolerances are required, the plastic category, (see classification), and the machining shape, turning or milling must be observed. For this, see the separate tables. Even tighter specifications must be agreed with our machining specialists.

Division of Plastics Regarding Dimensional Accuracy

Category "A"

Thermoplastics with low moisture absorption
and low expansion coefficient:
POM, PETP, PC, PPO, PVC, PP, PMMA, PEEK, PPS, PSU, PEI, PPSU, PBI, PAI, PCTFE, PVDF, Fluorosint

 

  • Image 1: Tolerances for turned parts
  • Image 2: Tolerances for milled parts

Category "B"

Thermoplastics with low strength, high moisture absorption and high expansion coefficient:
PE300, PE500, PE1000, Tivar, PTFE, PA6, PA6.6, PA6G, PA4.6, PA12, PA12G

 

  • Image 1: Tolerances for turned parts
  • Image 2: Tolerances for milled parts

DIN ISO 2768-1

Tolerance class up to 6 mm 6 to 30 mm 30 to 100 mm 100 to 300 mm 300 to 1000 mm
f (fine) +/- 0,05 +/- 0,1 +/- 0,15 +/- 0,2 +/- 0,3
#m (medium) +/- 0,1 +/- 0,2 +/- 0,3 +/- 0,5 +/- 0,8
c (coarse) +/- 0,2 +/- 0,5 +/- 0,8 +/- 1,2 +/- 2
v (very coarse) +/- 0,5 +/- 1 +/- 1,5 +/- 2 +/- 3

DIN ISO 2768-2

General tolerance for straightness and flatness

Tolerance class up to 10 mm 10 to 30 mm 30 to 100 mm 100 to 300 mm 300 to 1000 mm
H 0,02 0,05 0,1 0,2 0,3
#K 0,05 0,1 0,2 0,4 0,6
L 0,1 0,2 0,4 0,8 1,2

General tolerance for squareness

Tolerance class up to 100 mm 100 to 300 mm 300 to 1000 mm
H 0,2 0,3 0,4
#K 0,4 0,6 0,8
L 0,6 1 1,5

General tolerance for symmetry

Tolerance class up to 100 mm 100 to 300 mm 300 to 1000 mm
H 0,5 0,5 0,5
#K 0,6 0,6 0,8
L 0,6 1 1,5

Your contact person

  • Klaus Prior

    Klaus Prior

    Contact for quality assurance and scheduling
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