Rubber Molded Parts Mechanical Tolerances

Engineering, Manufacturing Tolerances

Mechanical Tolerances Rubber Molded Parts and Products

There are four levels of dimensional tolerances that are used for molded rubber products. “A1” High Precision “A2” Precision “A3” Commercial “A4” Basic

The level selected should be based upon the need with the following guidelines.

“A1” is the tightest tolerance classification and indicates a high precision rubber 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 post curing, do not lend themselves to Drawing Designation “A1” tolerances.

“A2” tolerances indicate a precision product. Molds must be precision machined and kept in good repair. While measurement methods may be simpler than the Drawing Designation “A1”, careful inspection will usually be required.

“A3” tolerances indicate a “commercial” product and will normally be used for most products.

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

When applying tolerances the following rules should be kept in mind.

  1. Fixed dimension tolerances apply 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.

Standard Dimensional Tolerance Table Molded Rubber Products Drawing Designation “A1” High Precision

Size (mm) Fixed Closure Size (inches) Fixed Closure
Above Incl. Above Incl.
0 -10 ±.10 ±.13 0 -.40 ±.004 ±.005
10 -16 .13 .16 .40 -.63 .005 .006
16 -25 .16 .20 .63 -1.00 .006 .008
25 -40 .20 .25 1.00 -1.60 .008 .010
40 -63 .25 .32 1.60 -2.50 .010 .013
63 -100 .32 .40 2.50 -4.00 .013 .016
100 -160 .40 .50 4.00 -6.30 .016 .020

Standard Dimensional Tolerance Table Molded Rubber Products Drawing Designation “A2” Precision

Size (mm) Fixed Closure Size (inches) Fixed Closure
Above Incl. Above Incl.
0 -10 ±.16 ±.20 0 -.40 ±.006 ±.008
10 -16 .20 .25 .40 -.63 .008 .010
16 -25 .25 .32 .63 -1.00 .010 .013
25 -40 .32 .40 1.00 -1.60 .013 .016
40 -63 .40 .50 1.60 -2.50 .016 .020
63 -100 .50 .63 2.50 -4.00 .020 .025
100 -160 .63 .80 4.00 -6.30 .025 .032
160 -& over 6.30 & over
multiply by .004 .005 multiply by .004 .005

Standard Dimensional Tolerance Table Molded Rubber Products Drawing Designation “A3” Commercial

Size (mm) Fixed Closure Size (inches) Fixed Closure
Above Incl. Above Incl.
0 -10 ±.20 ±.32 0 -.40 ±.008 ±.013
10 -16 .25 .40 .40 -.63 .010 .016
16 -25 .32 .50 .63 -1.00 .013 .020
25 -40 .40 .63 1.00 -1.60 .016 .025
40 -63 .50 .80 1.60 -2.50 .020 .032
63 -100 .63 1.00 2.50 -4.00 .025 .040
100 -160 .80 1.25 4.00 -6.30 .032 .050
160 -& over 6.30 & over
multiply by .005 .008 multiply by .005 .008

Standard Dimensional Tolerance Table Molded Rubber Products Drawing Designation “A4” Basic

Size (mm) Fixed Closure Size (inches) Fixed Closure
Above Incl. Above Incl.
0 -10 ±.32 ±.80 0 -.40 ±.013 ±.032
10 -16 .40 .90 .40 -.63 .016 .036
16 -25 .50 1.00 .63 -1.00 .020 .040
25 -40 .63 1.12 1.00 -1.60 .025 .045
40 -63 .80 1.25 1.60 -2.50 .032 .050
63 -100 1.00 1.40 2.50 -4.00 .040 .056
100 -160 1.25 1.60 4.00 -6.30 .050 .063
160 -& over - - 6.30 & over - -
multiply by .008 .010 multiply by .008 .010
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