Electropolishing Services: US Buyers’ Dimensional Comparison

Compare Able and Electro-Spec against the drawing, not their headline numbers: Able claims an alloy-dependent process tolerance of ±0.0001 inch; Electro-Spec lists typical material removal of 0.0001–0.0002 inch.[1][2] These describe different quantities and do not establish which shop can finish a particular stainless shaft or bore within tolerance.[1][2]

Compare the shops on the same three dimensions

Able Electropolishing

• Published dimensional statement: Able reports process tolerances as low as ±0.0001 inch, depending on alloy—not a typical material-removal range.[1]
• Applicability to the job: Able lists a 108 × 41 × 42-inch processing envelope for 300- and 400-series stainless steel and invites drawing submission for capability review.[1] Ask it to confirm the actual alloy, geometry and critical features.
• Trial-approval route: Able offers a free sample.[1] Ask what dimensional records and acceptance limits would accompany it; the sample offer is not dimensional approval.

Electro-Spec

• Published dimensional statement: Electro-Spec lists typical material removal of 0.0001–0.0002 inch. [2] Ask whether this means removal per surface or total dimensional change.
• Applicability to the job: The page identifies “Electropolishing Indiana.”[2] Applicable alloy and part-size limits for the drawing remain to be confirmed.
• Trial-approval route: Electro-Spec provides quote and contact routes.[2] Use them to request a measured trial and written dimensional acceptance terms rather than assuming an inspection package is included.

Ask Able what its tolerance claim controls and Electro-Spec how its removal figure is measured. Require both proposals to address the same critical drawing dimensions; neither published figure alone establishes a safe removal value for the part.[1][2]

Calculate the drawing’s remaining dimensional allowance

Start with the room between each measured feature and its drawing limit—not the shop’s typical removal figure. Allowance is stock intentionally left for later removal; tolerance is the permitted variation in finished size.[5]

Able describes electropolishing as removing surface metal, and Electro-Spec describes it as subtractive rather than a coating.[1][2] For the simplified shaft-and-bore geometry below, an outside diameter therefore gets smaller while an inside diameter gets larger.

Use these derived geometric headroom calculations, keeping starting measurements and drawing limits in the same units:

• Shaft diameter budget = measured starting outside diameter − drawing’s lower diameter limit.
• Bore diameter budget = drawing’s upper diameter limit − measured starting inside diameter.

These calculate room for diameter change, not removal depth at an individual surface. A result at or below zero leaves no positive headroom in the direction of removal. A positive result is not a validated process allowance: do not assume uniform removal or permission to consume the entire budget.

For engineering review, send the alloy, drawing revision, critical dimensions and limits, initial measurements with their locations, and relevant mating features. Ask about proposed racking or fixturing and its effect on those features. These are buyer-requested review inputs, not a published supplier checklist.

Ask the shop to propose feature-specific removal limits within the available headroom, reserving room for agreed measurement uncertainty and process variation before trial approval.

Distinguish per-surface removal from diameter change

A diameter spans opposing surfaces. The following hypothetical example shows why a per-surface removal value cannot be treated as the same amount of diameter change.

Hypothetical example—assumed uniform removal: These invented dimensions illustrate arithmetic only, not either provider’s capability or a recommended removal setting. Assume removal of 0.0001 inch radially from each opposing surface, uniformly at every measurement location.

• Shaft: The drawing permits a diameter of 0.4998–0.5002 inch; the measured starting diameter is 0.4999 inch. Remaining diameter budget: 0.4999 − 0.4998 = 0.0001 inch. Assumed diameter change: −2 × 0.0001 = −0.0002 inch. Result: 0.4999 − 0.0002 = 0.4997 inch, below the lower limit.
• Bore: The drawing permits a diameter of 0.5001–0.5005 inch; the measured starting diameter is 0.5004 inch. Remaining diameter budget: 0.5005 − 0.5004 = 0.0001 inch. The bore grows by 0.0002 inch. Result: 0.5004 + 0.0002 = 0.5006 inch, above the upper limit.

Both features fail their hypothetical drawing limits. Each has only 0.0001 ÷ 2 = 0.00005 inch of idealized radial headroom before reaching its limiting diameter, before any measurement or process margin. This is arithmetic, not a shop-approved safe removal limit.

Neither provider’s cited page establishes equal removal on opposing surfaces or at different measurement locations.[1][2] Do not insert Electro-Spec’s typical-removal range into the radial calculation until it confirms what the figure measures; Able’s process-tolerance claim is not a radial-removal value.[1][2]

Agree on a measured trial-lot acceptance plan

Put dimensional acceptance in writing before processing. The controls below are buyer-requested requirements for agreement, not inspection services already included by Able or Electro-Spec; neither shop’s cited page establishes a complete dimensional trial protocol.[1][2]

• Define the trial scope. Identify the drawing revision, stainless alloy, lot identification, proposed trial quantity and critical features. Agree which racking and handling conditions should represent production. Have engineering, quality and the shop agree on quantity rather than assuming a universal sample count.
• Map the measurements. Assign traceable part identifiers and measurement locations, including axial stations and orientations where relevant to the drawing. Request readings at the same locations before and after finishing.
• Agree on measurement capability. Specify instruments or methods and request the uncertainty or capability information engineering and quality need to judge readings against acceptance limits. Require paired readings and recorded changes for each agreed part and feature.
• Set numerical acceptance limits. Have engineering approve finished-dimension limits and, where needed, separate limits for process-induced change. Document how borderline readings will be handled, such as holding them for agreed remeasurement and engineering review, rather than inserting an arbitrary guard band.

Request a record with units stated explicitly and these fields:

• Part ID and lot identification.
• Feature and mapped measurement location.
• Drawing limits.
• Pre-process and post-process readings.
• Signed diameter change, with the sign convention defined.
• Agreed removal metric, distinguishing per-surface removal from diameter change.
• Disposition: accepted, rejected or held for review.

Ask for individual results, not just an average. Keeping each pre-process reading alongside its post-process reading helps separate incoming variation from finishing change; manufacturing background distinguishes variation already present in material from variation introduced during processing.[4]

Name the buyer’s engineering and quality reviewers and the shop contact responsible for discrepancies. Make trial acceptance contingent on the agreed records, measurement-capability information, deviation explanations and documented dispositions—not simply completion of processing.

Keep ASTM B912 separate from dimensional approval

ASTM B912-26 is the active Standard Specification for Passivation of Stainless Steels Using Electropolishing.[3] A standards reference belongs alongside dimensional approval, not in its place.

Its scope covers stainless steels in the 200, 300 and 400 series, plus precipitation-hardened alloys. It calls for basis material free of clearly visible defects, preparatory cleaning when necessary, and post-dip and final-rinse procedures.[3] Listed evaluation procedures include water immersion, humidity, salt spray, copper sulfate and modified ferroxyl testing for free iron; one or more may be used.[3]

ASTM’s abstract does not establish a permitted dimensional-removal range, finished roughness value or trial-lot dimensional acceptance plan.[3] Keep separate approval items in the purchase requirements:

• Process and testing acceptance: identify the applicable specification, selected evaluations and required evidence.
• Drawing-based dimensional acceptance: require the agreed measurement record to demonstrate compliance with drawing limits.

Treat these as separate signoffs. Passing selected passivation evaluations should not substitute for demonstrating acceptable finished dimensions.

Send both shops the same RFQ

Use Able’s quotation inputs as a starting point: drawing, requested service, lot and annual quantities, process specification, and packaging requirements.[1] Add the proposed measurement and acceptance plan so both shops can identify exceptions before quoting.

Ask both shops:

• What does your dimensional figure measure, and how does it apply to this alloy and the identified drawing features?
• What removal variation should the trial investigate across those features?
• Can you accept the proposed measurement locations, paired readings and reporting plan? Identify exceptions in the quotation.

Electro-Spec publishes a standard turnaround of five business days; Able offers same-day and next-day service at additional cost, without stating the surcharge.[1][2] Request a job-specific schedule covering the agreed inspection and reporting deliverables.

Able’s cited page does not state its service area, and neither shop’s cited page states fixed pricing, minimum order or term, warranty, or cancellation/refund terms.[1][2] Confirm shipping and job acceptance, and request written pricing for inspection and reporting, rework terms, and responsibility for scrapped parts.

Release production after reviewing the trial evidence

Make trial completion a review point, not automatic production authorization. The following workflow is a proposed buyer control; neither provider’s cited page establishes release signatures, change controls, rework policy or scrap liability.[1][2]

• Review the dimensional record. Compare every agreed critical measurement with the drawing and trial acceptance rules. Evaluate the direction and magnitude of finishing change separately from whether the final dimension passes.
• Resolve exceptions. Investigate missing readings, unexplained location-to-location differences and results near agreed acceptance boundaries. Do not treat an acceptable average as evidence of uniform removal. Hold production for engineering review if the trial fails or records are incomplete; do not assume further processing will recover the parts.
• Document authorization. Request written approval from the designated engineering or quality authority, tied to an identified process-plan revision and production inspection requirements.
• Define change-review triggers. Agree which changes to alloy, geometry, racking or process plan require buyer review. Treat these as job-specific purchasing controls, not universal requalification rules.

The proposed release gate is an accepted dimensional record, separately satisfied process/testing requirements, agreed commercial responsibility and explicit production authorization.

Choose on demonstrated dimensional compliance

Able’s drawing-review invitation and free-sample offer provide a route to qualification for parts within its published stainless processing envelope.[1] Electro-Spec’s Indiana identification and five-business-day standard turnaround provide purchasing context, but its typical-removal figure still needs a job-specific explanation.[2]

Select the supplier whose written proposal and accepted trial results demonstrate compliance with the drawing and agreed controls—not the supplier with the more attractive isolated number. Send both shops the same marked-up drawing and proposed before-and-after acceptance checklist before authorizing production.

References

1. Electropolishing Service for Stainless Steel & Other Metal Parts | Able (ableelectropolishing.com)
2. Electropolishing Services | Electro-Spec (electro-spec.com)
3. B912 Standard Specification for Passivation of Stainless Steels Using Electropolishing (astm.org, 2026)
4. Sheet Metal Tolerances Guide with Charts and Standards (komacut.com)
5. Machining Allowance (3erp.com)