Silicone part tolerances: what to put on the drawing
Silicone tolerances depend on feature size, compound, molding or extrusion process and measurement conditions. Agree them for the specific part before tooling.
Distinguish specification from capability
A drawing tolerance is an acceptance requirement, not evidence that a process can hold it. Identify functional dimensions and datums, explain assembly constraints and request dimensional results from representative samples. Mold steel tolerances do not automatically become finished-part tolerances.
Use the right tolerance framework
ISO 3302-1 covers molded, extruded and calendered solid rubber products. Use the classes applicable to the production method: do not apply an extrusion E-class table to a molded part by default. Check the current standard, dimension range and fixed or closure dimension as relevant.
Define how the part is measured
Agree cure and post-cure state, conditioning, measurement method, support fixture and any contact force that could deform the silicone. Separate measurement uncertainty from process variation. Define sampling and cavity identification where they matter to acceptance.
Before requesting a quote
Send the drawing revision, application, material preference, critical dimensions, annual quantity, delivery market and required evidence. Feasibility, testing, price and timing need written project review.
Buyer questions
Does LSR guarantee ±0.05 mm?
No. A process name cannot guarantee a tolerance across all geometries and compounds. Obtain a written feature-specific agreement supported by tool review and sample measurement.