Electropolishing Allowances: Protect Holes, Fits and Thin Edges

An electropolishing note can be technically clear about the process and still be incomplete about the part. If the drawing does not identify the final acceptance state, the supplier may inspect a locating hole before treatment while the buyer checks it afterward. Both teams can follow their own interpretation and disagree at delivery.

For precision OEM sheet metal, finish planning and dimensional planning must meet at the same released drawing. This article focuses on that handoff. For the process-selection question, see passivation versus electropolishing.

Mark the features sensitive to material removal

Identify holes used for location, narrow slots, thin tabs, mating edges, threaded features and any face involved in a controlled fit. A large cover can have a generous outer envelope and still contain one sensitive locating interface.

Ask the selected processor to review the actual geometry and proposed route. Able’s specification guidance discusses specifying material removal and dimensional requirements. Its stated capabilities belong to that supplier; they must not be copied into another fabricator’s quotation.

Do not assume all surfaces receive identical removal. Access, geometry and the approved process need review. Where a critical feature cannot accommodate the proposed route, resolve the design or process choice before the batch is released.

Use a budget, not an assumed universal allowance

Consider a deliberately simplified example: a cylindrical opening starts at 10.00 mm and a hypothetical uniform 0.01 mm is removed from each opposing wall. The resulting diameter would be 10.02 mm. If the removal in this illustration ranged from 0.005 to 0.015 mm per wall, the resulting diameter would range from 10.01 to 10.03 mm before considering the starting-hole variation.

This is arithmetic for understanding a tolerance budget, not a recommended removal amount or process capability. Real holes and sheet edges require a project-specific assessment. An outer dimension responds in the opposite direction when material is removed from its external faces, but that simple relationship still does not capture nonuniform processing.

Use the exercise to ask which variation is already present before finishing and how much remains available afterward. Do not ask the processor to compensate for an uncontrolled starting dimension.

Define the inspection stage for each requirement

A drawing can require an intermediate check for manufacturing control and a final check for acceptance. Name both when needed, and avoid making the buyer infer the distinction from an old inspection report.

Specify the support and datum conditions for flexible parts. A measurement that bends a thin panel into a fixture can answer a different question from a free-state measurement. Use the condition intended by the responsible designer.

Review masking and alternative sequences explicitly

A buyer may ask whether selected features can be protected or processed differently. Treat that as a process-development question for the chosen geometry, not as an automatic solution.

If a different sequence is approved, document the operations and the final condition. Reaming, installing hardware or adjusting a surface after finishing can affect the accepted part and may require additional review. Do not make such changes informally to recover a failed fit.

The stainless hardware guide addresses installed fasteners and treatment sequence. Coordinate the two reviews where a panel includes both a locating feature and clinched hardware.

Make the first-piece evidence relevant to the batch

Choose a representative part and a record that identifies its drawing, material, starting condition and approved route. A flat sample may inform surface selection but does not necessarily represent the removal behavior of a deep return or a small hole.

Agree what must be re-reviewed if the part geometry, processor route or material condition changes. A previously accepted sample should not be treated as unlimited approval for different parts.

Give the quotation a defined dimensional boundary

For a stainless sheet metal RFQ, supply the critical-feature map, final drawing requirements, initial condition, proposed treatment and expected records. Request a processor review where the tolerance budget is sensitive.

A reliable quotation can identify an unresolved allowance or an unsuitable route. That answer is more useful than a blanket promise that electropolishing will improve every surface without affecting any fit.