Build to Print Machining Explained: What a Complete Drawing Package Includes

Build to print machining means the shop manufactures your part exactly as your drawing specifies, with no design changes and no reverse engineering. You own the design, you own the print, and the machine shop owns the execution. The single biggest factor in a smooth build to print job is the quality of the drawing package you hand over. A clean, complete package cuts quoting time, prevents scrap, and locks in a repeatable process. A vague one leads to change orders, rework, and schedule slips.

This guide covers exactly what belongs in a production-ready build to print drawing package, with the tolerance, finish, and inspection detail that a precision CNC shop actually uses on the floor.

What Build to Print Machining Actually Requires

In a true build to print arrangement, the shop does not alter geometry, features, or callouts. If something on the print is unmanufacturable or economically painful, the shop flags it and requests a deviation or engineering change, but it will not silently "fix" it. That is why the drawing package has to stand on its own. Everything the machinist, programmer, and inspector need must be on the page.

The core documents in a complete package

• 2D drawing (PDF or paper) with title block, revision level, units, and default tolerance block.
• 3D model (STEP or Parasolid) for CAM programming. A native STEP AP242 file carries product manufacturing information cleanly.
• Bill of material or notes covering material grade, temper, and any coatings or platings.
• Inspection requirements, including which dimensions are critical and whether first article inspection is required.

Tolerances: Be Specific, Not Blanket

The fastest way to overpay for a machined part is to apply one tight tolerance to the entire print. Most features do not need to be held to a precision limit. Call out tolerances by feature and reserve the tight ones for what actually matters.

Typical tolerance tiers a CNC shop works to:

• General machining: +/-.005 in on non-critical features.
• Precision fits: +/-.001 in for bearing bores, dowel holes, and mating surfaces.
• Tight tolerance: +/-.0005 in or tighter for close-fit pins, seals, and gauge features, often achieved with Swiss machining on small diameters.

Pair the tolerance callout with a surface finish spec. Common targets are Ra 63 uin for as-machined faces, Ra 32 uin for sealing surfaces, and Ra 16 uin for fine bearing or seal contact areas. If you leave finish blank, you get whatever the tool and feed produce, which may not be what you expected.

GD&T that earns its place

Geometric dimensioning and tolerancing communicates function, not just size. A good package uses GD&T deliberately: flatness on a mounting face, position on a bolt pattern, concentricity between a bore and an OD. Define your datum reference frame clearly so the datums match how the part is fixtured and how it will be inspected on a CMM. When datums are ambiguous, the measured result depends on setup, and arguments follow.

Material Callouts and Certifications

Spell out the exact material grade and condition. "Aluminum" is not a spec. "6061-T6511 extruded bar" is. Typical grades a shop stocks or sources routinely:

• Aluminum: 6061-T6, 7075-T651, 2024-T3.
• Stainless: 303, 304, 316, 17-4 PH.
• Steel: 1018, 4140, 4340, 12L14.
• Plastics: Delrin, PEEK, PTFE, Nylon 6/6.

If your part is destined for aerospace, defense, or a regulated market, state whether you need material certs, DFARS-compliant material, or full traceability. A shop that is SAM.gov and CAGE registered can carry these requirements, but only if the print or PO calls for them. See our government and defense machining page for how traceability flows through a build to print job.

Inspection: First Article and CMM

State your inspection expectations on the drawing or in the PO. Options a build to print shop supports:

• First article inspection (FAI), often to an AS9102-style format, verifying every dimension on the print before the run.
• In-process CMM inspection on a Brown & Sharpe coordinate measuring machine for critical GD&T features.
• Dimensional report with actual measured values, ballooned to the print.

Ballooning the drawing (numbering each dimension) makes FAI faster and cheaper because the inspector maps measured values straight to numbered features. If you can, deliver a pre-ballooned print or allow the shop to balloon it for you.

Build to Print Cost Drivers

The table below shows typical illustrative ranges for a mid-complexity build to print part in aluminum or mild steel. These are planning estimates, not binding quotes. Actual pricing depends on your geometry, quantity, material, and inspection level. Get a firm number from our instant quote tool.

How quantity moves the number

Setup and programming are fixed costs spread across the lot. A one-off part carries the entire setup cost, so a single unit can cost several times the per-piece price at a run of 100. If you expect volume, tell the shop up front so the process is built for repeatability, not just a single good part.

A Build to Print Package Checklist

1. Dimensioned 2D drawing with revision, units, and default tolerance block.
2. 3D STEP model matching the drawing revision.
3. Feature-specific tolerances and surface finish callouts.
4. Clear GD&T and a defined datum reference frame.
5. Exact material grade, temper, and coating.
6. Certification and traceability requirements stated explicitly.
7. Inspection level defined: FAI, CMM report, or standard.
8. Quantity and delivery expectations.

Hand a machine shop a package like this and build to print machining runs the way it should: predictable, traceable, and right the first time. Wexmar is a precision CNC machine shop in Canastota, NY running turning, milling, and Swiss platforms with in-house CMM inspection and an ISO 9001-aligned quality system. Review our machine list to see the equipment your part would run on.