FAQ

For most CNC machining RFQs, STEP (.stp / .step) is preferred because it carries solid model geometry without the ambiguity of older 2D-only workflows. IGES is acceptable for many parts, though surface trims and translations can occasionally introduce gaps that require cleanup.

Please also include 2D drawings (PDF) when tolerances, GD&T, threads, surface finish, or inspection requirements are not fully modeled. For turned parts, a drawing with section views and thread callouts is especially helpful.

If you only have mesh formats (STL), we can review feasibility, but prismatic and tolerance-critical parts are best quoted from precise B-rep solids. ZIP archives with multiple revisions should include a short note indicating which revision is current.

Lead time depends on complexity, material availability, finishing steps, and current shop load. Simple prismatic parts in common alloys often fall into a standard window quoted case-by-case, while tight-tolerance work, hard metals, or multi-op assemblies may require additional planning.

Expedited schedules are sometimes possible when drawings are complete, materials are specified without ambiguity, and inspection criteria match the actual critical features on the print.

The fastest way to shorten cycle time is a clean RFQ: stable revision, clear critical dimensions, and consolidated finishing notes so engineering and programming can start without back-and-forth.

“Typical” tolerances are not universal—they depend on feature type, material, part size, tooling access, and inspection method. Many drawings use a general tolerance block (for example ±0.1 mm) with tighter callouts only where function requires it.

For communication during quoting, it helps to separate critical dimensions from nice-to-have targets. Over-tightening non-functional surfaces can add cost without improving assembly fit.

If you need very tight bore or thickness control, say whether grinding or secondary lapping is acceptable. Sometimes a slightly looser machined tolerance plus a controlled secondary op is more reliable than pushing everything in one setup.

CNC is naturally flexible: low volumes and prototypes are common when programs and fixturing can be amortized across future repeats. True “MOQ” pressure more often comes from material buy quantities, outside processes (plating, heat treat), or tooling unique to the part.

For prototypes, we recommend aligning the drawing revision, material grade, and finish with what you intend for production—otherwise you may optimize the wrong iteration.

If you expect a ramp from prototype to production, mention expected annual usage so setup and inspection plans can scale without surprises.

Most machine shops routinely work aluminum alloys, carbon and alloy steels, stainless steels, brass and copper alloys, and selected plastics for functional prototypes and production parts. Specialty alloys and hard metals may require slower cutting strategies and different tooling.

The “right” material is the one that meets strength, corrosion, weight, and cost targets as specified on the drawing. If a substitution is proposed, it should be reviewed for mechanical equivalence and any downstream finishing compatibility (anodize, weld, passivate).

For food, medical, or marine exposure, call out the governing standard or grade family so material certificates and traceability can match your quality plan.

Design for manufacturability (DFM) means aligning geometry, tolerances, and material choices with how parts are actually fixtured, cut, deburred, and inspected. Good DFM reduces scrap risk, stabilizes cycle time, and avoids “impossible” blends of tolerance and access.

Examples include adding relief for internal corners, avoiding unnecessary deep pockets with small radii, and consolidating datum references so inspection matches fabrication.

A practical DFM review before cutting metal often pays for itself by preventing late-stage rework when assembly or coating processes reveal an unmachinable edge condition.

Surface finish should connect to function: sealing faces, bearing fits, cosmetic areas, and bonding surfaces often need different controls. A common approach is to call out Ra (or Rz) on critical faces and use a general note for “as-machined” elsewhere.

For cosmetic parts, specify whether tool marks are acceptable and whether directional grain (brush) is required. For coatings, note masking boundaries and any blast or prep steps.

If only one side of a plate must be flat for gasket sealing, say so explicitly—otherwise shops may assume uniform finish across non-critical faces.

Turning rotates the workpiece against a stationary tool and is ideal for shafts, bushings, and axisymmetric features. Milling fixes the workpiece (or moves it on multi-axis machines) while rotating cutters remove material—better for prismatic housings, pockets, and complex contours.

Many parts use both: turned blanks with secondary milled features, or round stock prepared on a lathe then completed on a mill.

Choosing the primary process is usually driven by which surfaces define the part’s function and how efficiently material can be removed while holding datums.

Inspection deliverables should match your quality plan. Typical options include dimensional reports keyed to the drawing, first-article layouts for new programs, and CMM datasets when tight features are involved.

To avoid ambiguity, specify which features are critical for acceptance and what sampling plan applies (for example per batch vs. per order). If you need material certificates, call out the required documentation level up front.

Advanced inspection adds time but reduces downstream risk—especially for assemblies where a single bore or face controls stack-up.

Mixed-process parts (for example stamp + machine + plate) need a clear sequence: which features are created in which operation, and which datums carry through heat treat or coating.

Use revision control so outside service providers (OSP) always see the same drawing level. If one vendor does blanking and another does machining, note allowable stock for cleanup passes.

When possible, consolidate critical dimensions on a single view with explicit datum references rather than scattering tight tolerances across unrelated views.

Heat treatment changes microstructure to adjust hardness, toughness, or stress state. Common goals include increasing wear resistance, relieving residual stress after machining, or preparing material for subsequent hardening.

Call out the required spec (for example a standard or hardness range) and whether distortion limits matter for downstream machining or grinding.

Some finishes (like certain plating) also need bake cycles for hydrogen embrittlement concerns on high-strength steels—your drawing stack should mention process constraints when applicable.

Responsible suppliers treat CAD and drawings as confidential business information. Practical measures include access-controlled storage, least-privilege sharing inside the shop, and clear retention policies aligned to your NDA.

For RFQs, share the minimum geometry needed to quote—watermarked PDFs or simplified step files can reduce exposure during early discussions.

If you require a formal NDA before file transfer, send it early so procurement and engineering can align on signing authority and scope.