Tolerances and cut-to-size material: how to write a usable order

Finished size and stock size are different

A drawing specifies the finished component; the purchased bar may need machining and workholding allowance. Confusing the two can leave correctly cut material unsuitable for production. State diameter and length for rounds, thickness and width for flats, side length for squares, and across-flats size for hexagons. The across-corners dimension of a hexagon is not the same as its across-flats dimension.

There is no single machining allowance suitable for every grade and dimension. Rolled or forged surfaces, straightness, the finishing sequence and component geometry influence the allowance. The production owner should assess the required finished size and surface together when defining stock. An unnecessarily large section can also increase material removal, machining time and cost.

Tolerance is more than one number

Diameter tolerance, out-of-roundness, straightness, surface quality and cut length are separate acceptance issues. A ground surface does not automatically establish the fit required for a precision assembly. Likewise, a sawn end does not automatically meet finished-part squareness, parallelism or roughness requirements. Distinguish the required finishing operation and measurement method in the enquiry.

EN 10278 addresses dimensions and tolerances for bright steel products; ASTM A484 covers general requirements for stainless bars and other specified product forms. Citing either standard alone does not fully define alloy identity, all dimensional classes or special cutting acceptance. Clarify the applicable product standard, revision and any separately agreed requirements together.

Check the cutting list

Use a separate line for each size. For example, list 316L / 1.4404, round bar, purchased diameter, cut length and quantity, followed by tolerance and documentation requirements. This template is not a promise of capacity or tolerance; confirmation depends on grade and dimensions. Ensure quotations are compared on the same allowance, surface condition and cut-length acceptance basis. Update the cutting list if the manufacturing sequence changes: cutting before surface finishing and cutting an already finished bar may require different purchasing descriptions.

• State the unit and whether length tolerance is unilateral or bilateral.
• Specify quantity, supplied surface and deburring expectations.
• Include batch identification and certificate requirements in the cutting list.