High Precision Tolerance for Molded Rubber Parts

The Rubber Manufacturers Association “A1” designation is the tightest tolerance classification and indicates a high precision molded rubber product.

Parts that designated ‘A1’ can require advanced tooling and complex molds with fewer cavities per mold, robust in-process controls, and greater inspection procedures.

The table below indicated the different levels of tolerance for molded rubber components.

Of course, the method of measurement is a key consideration. Some materials, particularly those requiring a post curing operation, or designs with an allowable level of flash do not lend themselves to drawing designation “A1” tolerances. Please contact Rahco Rubber for specific recommendations.

 

Size (Inches)		Fixed	Closure		Size (Millimeters)		Fixed	Closure
Above — Including 0.000” – 0.100” 0.101” – 0.190” 0.191” – 0.382” 0.383” – 0.695” 0.696” – 1.064” 1.065” – 1.564” 1.565” – 2.064” 2.065” – 2.564” 2.565” – 3.064” 3.065” –  4.064” 4.065” –  5.064” 5.065” –  6.064”		Tolerances ± .002” ± .003” ± .004” ± .005” ± .006” ± .008” ± .009” ± .010” ± .012” ± .013” ± .015” ± .016”	Tolerances ± .004” ± .005” ± .006” ± .007” ± .008” ± .010” ± .011” ± .012” ± .014” ± .015” ± .017” ± .018”		Above — Including 0.000 – 2.540 2.570 – 4.830 4.830 – 9.700 9.730 – 17.650 17.680 – 27.030 27.050 – 39.730 39.750 – 52.430 52.450 – 65.130 65.150 – 77.830 77.850 – 103.230 103.250 – 128.630 128.650 – 154.030		Tolerances ±0.050 ±0.080 ±0.100 ±0.130 ±0.150 ±0.200 ±0.230 ±0.250 ±0.300 ±0.330 ±0.380 ±0.410	Tolerances ±0.100 ±0.130 ±0.150 ±0.180 ±0.200 ±0.250 ±0.280 ±0.300 ±0.360 ±0.380 ±0.430 ±0.460

 

RMA DESIGNATIONS

“A1” HIGH PRECISION

Drawing designation “A1” is the tightest tolerance classification and indicates a high precision product. Such products require expensive molds, fewer cavities per mold, costly in-process controls and inspection procedures. It is desirable that the exact method of measurement be agreed upon between rubber manufacturer and customer, as errors in measurement may be large in relation to the tolerance. Some materials, particularly those requiring a post curing operation after molding, do not led themselves to drawing designation “A1” tolerances

“A2” PRECISION

The A2 tolerance indicates a precision product. Molds must be precision machined and kept in good repair. While measurement methods may be simpler than the drawing dimension A1, careful inspection will usually be required.

“A3” COMMERCIAL

The A3 tolerances indicate a ‘commercial’ product and will normally be used for most products and non-critical applications for which precision molding is not required.

“A4” BASIC

The A4 tolerances apply to products where some dimensional control is required but is secondary to cost.

 

When applying tolerances the following should be considered:

1. Fixed dimension tolerance apply to individually to each fixed dimension by its own size.
2. Closure dimension tolerances are determined by the largest closure dimension and this single tolerance is used for all other closure dimensions.
3. Fixed and closure dimensions for a given table do not necessarily go together, and can be split between tables.
4. Tolerances not shown should be determined in consultation with the rubber manufacturer.
5. Care should be taken in applying standard tolerances to products having wide sectional variations.

Please contact Rahco Rubber for specific recommendations.

 

Factors Affecting Tolerances

Learn more in this guide on the Standard For Dimensional Tolerances. The degree of reproductivity of dimensions depend on the type of tooling and rubber used, and general capabilities, processes and technology used in manufacturing.

Among the many factors in the manufacturing of molded rubber parts which affect tolerances, the most common include:

• Shrinkage
• Mold Design
• Tim and Finish
• Inserts
• Distortion
• Environmental Storage Conditions
• Dimension Terminology (Fixed and Closure)
• Measurement of Dimensions
• Relative Dimensions

Read more here Standard For Dimensional Tolerances.