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Each dimension on your plastic extruded profile has a tolerance, but what is a tolerance and why is it important?

A tolerance provide a manufacturer allowance for a specific dimension to be larger or smaller than nominal, but still be within specification.  For instance, a length tolerance may be 48.00” +/- 0.5”.  This means that the length of the extrusion can be anywhere between 47.50” or 48.5” and still be deemed acceptable to the manufacturer and to the user.

Tolerances are determine based on several factors:

  1. Application of the extrusion (fit and function)
  2. Manufacturing capabilities
  3. Cost

Application of the Extrusion (Fit and Function): Any product must work in its application, which may include a need for specific functionality or the need for the product to work with mating parts.

Manufacturing Capabilities: New technologies in extrusion equipment, extrusion tooling, and thermoplastic materials allow for tight tolerances to be held in the plastic extrusion process.  For instance, changing output rates to improve control of the product during the extrusion cooling process, adding vacuum calibration, or using high quality plastic compounds are options that can help tighten tolerances.

Cost: If tolerances are extremely tight, some work may need to be done offline, contributing to higher costs resulting from increased time needed to manufacture the product and/or increase handling of the product.  Balancing the need for tight tolerance and economic considerations is important when designing a plastic extrusion.

What Tolerances are Typical?

The below table details typical tolerances for a variety of thermoplastic materials.  This table is for reference only.  Contact us to discuss your profile and typical tolerances.

 Rigid PVCPolystyreneABS/
Polycarbonate
PolypropyleneFlexible PVCPolyethylene
Wall Thickness (+-)8%8%8%8%10%10%
Angles (+-)2 Degrees2 Degrees3 Degrees3 Degrees5 Degrees5 Degrees
Profile Dimensions (+-)
To .125"0.007"0.007"0.010"0.010"0.010"0.012"
0.126" to 0.500"0.010"0.012"0.020"0.015"0.015"0.025"
0.501" to 1.000"0.015"0.017"0.025"0.020"0.020"0.030"
1.001" to 1.500"0.020"0.025"0.027"0.027"0.030"0.035"
1.501" to 2.000"0.025"0.030"0.035"0.035"0.035"0.040"
2.001" to 3.000"0.030"0.035"0.037"0.037"0.040"0.045"
3.001"to 4.000"0.045"0.050"0.050"0.050"0.065"0.065"
4.001 to 5.000"0.060"0.065"0.065"0.065"0.093"0.093"
5.001 to 7.000"0.075"0.093"0.093"0.093"0.125"0.125"
7.001" to 10.000"0.093"0.125"0.125"0.125"0.150"0.150"
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