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
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
Contact for quality assurance and scheduling- +49 (0) 29 92 / 97 60 - 25
- +49 (0) 29 92 / 97 60 - 20
- k.prior@kuhn-marsberg.de