You specify C360 brass on the drawing, the parts arrive to correct dimensions, but the alloy turns out to be zinc-based. No material test certificate means you discover the problem only when a batch of brass insert nuts corrodes on the assembly line. This gap between the written spec and verified material is where most sourcing disputes begin.
What Material Testing Should CNC Buyers Ask For
Most RFQs list "brass" or "304 stainless" and leave it at that. The test method matters as much as the material name. For copper, brass, and bronze precision turned parts, a XRF spectroscopy report confirms the alloy grade against your drawing. For stainless steel bushings or threaded inserts, a positive material identification check catches 400-series contamination that dimensional gauges will never detect. A drawing revision that changes the material grade should trigger a new test, not reuse the old report.
Weeda Precision includes material verification in the inspection package for CNC turning and multi-axis machining orders. The test is matched to the part spec at the quote stage, so the report you receive proves the right thing without a follow-up email.
How Much Material Testing Fits Your Order Volume
A prototype run of 50 shafts or sleeves doesn't need the same depth as an annual contract for 200,000 units. For the small batch, a thread gauge check on critical fits plus a surface finish reading covers the real risk. Once volume scales, request a first-article inspection report that bundles the material cert, dimensional report, and finish measurement into one document. Packaging and lead time should also reflect the inspection hold: budget two extra days for the material test before shipment.
State the sample quantity directly in the RFQ. Three pieces per lot for destructive testing, the remainder for dimensional only. This keeps verification cost proportional to order size while still catching the defects that would stop a production line downstream.
Write the material test requirement on the drawing or RFQ, not in a side email thread that gets lost in the revision history. Name the test standard, the sample count, and who issues the report. One clear line on the print saves a weeks-long argument after the parts arrive and the drawing revision has already moved on.