As Formed Tolerances

Dimensions formed over projections (Figure 18 E and F) can normally be held to +/- .010 for the first inch, plus +/- .001 inches per inch for each additional inch, up to 50 inches with a maximum tolerance of +/- .062 for dimensions greater than 50 inches.

Outside dimensions (Figure 18 A, B, C and D) can normally be held to +/- .015 for the first inch, plus +/- .002 inches per inch for each additional inch.

For formed dimensions between one tool surface and one non-tool surface on relatively simple piece parts (Figure 18 B and C), add one material thickness variation (approximately +/- 5% of the material's starting thickness) to the previously stated tolerances. For formed dimensions between two non-tool surfaces on relatively simple piece parts (Figure 18 L), add two material thickness variations (approximately +/- 10% of the material's starting thickness) to the previously stated dimension tolerances. For more complicated piece parts where local draw ratios vary widely from the average draw ratio, provide additional tolerance allowance or secondary machining. A competent Thermo Pressure Former can advise you as to what tolerances are practical.

It is not customary to specify dimensions on those thermoformed surfaces which are not formed in contact with the die (non-tool surfaces). If precision dimensions must be provided on these non-tool surfaces, the tolerances must be broad as previously discussed, or these dimensions can be provided for secondary machining. However, providing precision dimensions on non-tool surfaces may result in additional part costs and a one-time charge for the added tooling.

It may be possible to hold tighter tolerances than those indicated above. However, the reject rate, cycle time and part cost may be prohibitively high.