{"id":2238,"date":"2026-07-04T03:48:00","date_gmt":"2026-07-03T19:48:00","guid":{"rendered":"https:\/\/metalstampingparts.ltd\/?page_id=2238"},"modified":"2026-07-04T03:48:00","modified_gmt":"2026-07-03T19:48:00","slug":"stamped-part-datum-functional-gage-guide","status":"publish","type":"page","link":"https:\/\/metalstampingparts.ltd\/stamped-part-datum-functional-gage-guide\/","title":{"rendered":"Stamped Part Datum and Functional Gage Guide"},"content":{"rendered":"

Short answer:<\/strong> Stamped part datums should match how the part is located in the final assembly, not only what is easiest to measure on a bench. Thin, formed, or spring-like parts may need a functional gage, restrained check, or clear free-state requirement so buyer and supplier measure the same condition.<\/p>\n

Stamped parts can be flexible, curved, burred, plated, or slightly warped in free state. A CMM report may look different from a fixture check if the datum scheme is unclear. This creates arguments even when the part functions correctly in assembly. A good RFQ explains how the part is located, constrained, and accepted.<\/p>\n

Use this page with the critical dimensions inspection plan<\/a>, Gage R&R and MSA guide<\/a>, FAI checklist<\/a>, and tolerances guide<\/a>.<\/p>\n

Datum and gage decisions<\/h2>\n\n\n\n\n\n\n\n\n
Decision<\/th>\nRisk if unclear<\/th>\nRFQ detail<\/th>\n<\/tr>\n<\/thead>\n
Primary datum<\/td>\nSupplier may measure from a surface that does not control assembly fit.<\/td>\nState the functional locating surface, hole, edge, or formed feature.<\/td>\n<\/tr>\n
Free-state or restrained<\/td>\nFlexible parts can pass one method and fail another.<\/td>\nDefine whether the part is clamped, nested, or measured without force.<\/td>\n<\/tr>\n
Functional gage<\/td>\nCMM data may not reflect actual assembly condition.<\/td>\nAsk whether a go\/no-go or checking fixture is needed.<\/td>\n<\/tr>\n
Correlation<\/td>\nBuyer and supplier may not agree on measurement method.<\/td>\nDefine master samples, gage calibration, and report format.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Choose datums from function<\/h2>\n

The best datum scheme usually starts with the assembly. Holes that locate on pins, tabs that seat against a bracket, or formed faces that contact a mating part may deserve datum priority. A long sheared edge may be easy to probe, but it may not control the part in the real product.<\/p>\n

For thin sheet metal, a datum surface can be affected by flatness, coating, burr direction, or forming stress. If the part is measured in free state, the drawing should say so. If the customer assembly restrains the part, the inspection method should describe the restraint.<\/p>\n

When a functional gage helps<\/h2>\n

A functional gage is useful when the buyer cares about fit more than isolated coordinate data. It can check whether mounting holes align, tabs seat, clips engage, or a bracket clears a mating component. The gage does not replace all dimensional inspection, but it can prevent a shipment of parts that measure acceptably and still fail assembly.<\/p>\n

The quote should state whether gage cost is included, who owns the gage, how it is calibrated, and whether the buyer wants gage correlation samples. For measurement variation, connect the gage plan with the inspection equipment guide<\/a> and coplanarity guide<\/a>.<\/p>\n

RFQ details to include<\/h2>\n