CNC machining frequently asked questions

Send a 3D CAD model plus a controlled 2D drawing when the model does not fully define the part. Identify the part number and revision, units, material specification and condition, quantity or quantity breaks, critical dimensions and GD&T, threads, surface texture and finish, inspection and certificate requirements, and requested delivery date. State the governing drawing and acceptance standards. Complete, revision-matched files reduce clarification time and let engineering assess manufacturing and inspection risk before quoting.

Answer owner: PiPrecision Engineering Team

STEP or STP is preferred for solid 3D geometry, and PDF is preferred for the controlled 2D drawing. The upload system also accepts IGES or IGS, SLDPRT, STL, OBJ, 3MF, DXF, and DWG files, including ZIP or RAR packages. Tessellated formats such as STL, OBJ, and 3MF may be adequate for reference but are less suitable than solid CAD for precision machining. Provide a revision-matched 2D drawing for GD&T, threads, fits, surface-texture callouts, notes, and other requirements not reliably carried by the model.

Answer owner: PiPrecision Engineering Team

Provide a formed 3D model and a controlled 2D drawing with part number, revision, units, material specification and thickness, inside bend radii, bend direction and sequence where critical, grain-direction restrictions, critical dimensions and datums, hardware, weld symbols, edge and burr requirements, finish, and inspection scope. State whether formed dimensions or the supplied flat pattern control acceptance. Unless otherwise agreed, the manufacturer should develop the production flat pattern using the selected tooling and validated bend allowance rather than treating an unqualified customer flat as final.

Answer owner: PiPrecision Engineering Team

The published 800 × 600 × 500 mm figure is a machine travel or work-envelope reference, not a guaranteed finished-part size. Usable capacity is smaller when fixtures, rotary axes, tool length and access, part loading, material weight, feature depth, or inspection access consume the envelope. Send the complete part and stock dimensions; engineering must confirm the machine, setup, reach, workholding, and tolerances for every large, thin, heavy, or distortion-sensitive part.

Answer owner: PiPrecision Engineering Team

Indexed 3+2 machining positions the part and cuts with the rotary axes locked; simultaneous 5-axis machining moves linear and rotary axes together during the cut. Either can reduce setups for multiple faces, compound angles, or difficult tool access and may improve relationships between features made in one setup. Simultaneous 5-axis work adds programming, collision-control, toolpath, and verification demands, so it is not automatically more accurate or economical. PiPrecision selects the method from geometry, tolerance, surface, quantity, and inspection needs.

Answer owner: PiPrecision Engineering Team

Common candidates include aluminum, stainless steel, carbon and alloy steels, titanium, brass, copper, and engineering plastics. Feasibility is confirmed by exact grade, temper or heat-treatment condition, stock form, dimensions, quantity, required certificates, and final finish. Substitute grades are not assumed. Plastics may also require moisture-conditioning, temperature, stress-relief, or inspection-state requirements because they can move with humidity, temperature, and machining stress.

Answer owner: PiPrecision Engineering Team

Published machine references include approximately 1-32 mm bar diameter for Swiss turning and turning capacity up to 300 mm diameter and 600 mm length on conventional equipment. These are not a guaranteed finished-part envelope: chucking or collet length, bar-stock tolerances, through-bore, sub-spindle transfer, tailstock or steady-rest support, tool access, material, and part geometry can reduce usable capacity. Engineering confirms the process from the drawing, stock size, quantity, and inspection requirements.

Answer owner: PiPrecision Engineering Team

Swiss-type turning is often suitable for small-diameter, slender, or complex parts made from bar stock because the guide bushing supports the material close to the cutting zone. It can also combine turning, drilling, cross-holes, flats, threads, and back-working in one cycle. Bar straightness and diameter, guide-bushing compatibility, length-to-diameter ratio, remnant and cutoff allowances, material, tolerance, and production quantity determine whether Swiss-type or conventional turning is the better process.

Answer owner: PiPrecision Engineering Team

Start with function: substrate and condition, corrosion environment, wear, friction, electrical conductivity or insulation, chemical and temperature exposure, appearance, and regulatory needs. Then specify the process and governing standard, coating class or thickness, color standard, gloss or texture, sealing or post-treatment, masking, contact points, and inspection or test method. Finish names alone are not complete specifications; PiPrecision reviews compatibility, dimensional allowance, cosmetic limits, and supply-chain availability before commitment.

Answer owner: PiPrecision Engineering Team

Masking and post-finish marking can be reviewed, but feasibility depends on geometry, process temperature and chemistry, required edge quality, and contact or rack locations. Define masked threads, bores, grounding points, sealing faces, cosmetic zones, and allowed witness marks on the drawing. For laser marking, provide controlled artwork or text, location, orientation, size, contrast, serialization rules, machine-readable-code grade if applicable, and permanence or qualification requirements.

Answer owner: PiPrecision Engineering Team

Published cutting references cover common carbon steel and aluminum from about 0.5-6.0 mm and stainless steel from about 0.5-5.0 mm. Forming capability can be more restrictive than cutting capability. Exact limits depend on alloy and temper, stock availability, sheet and blank size, coating or protective film, hole-to-edge and hole-to-bend distances, inside radius, flange length, bend length and tonnage, tooling, grain direction, and cosmetic requirements. Engineering confirms both cutting and forming feasibility from the drawing.

Answer owner: PiPrecision Engineering Team

PiPrecision can review self-clinching hardware, TIG or MIG welding, resistance spot welding, mechanical assembly, and finishing as part of a sheet-metal project. Specify the hardware manufacturer, exact part number and installation orientation; material condition and finish sequence; weld symbols, process or code, filler and workmanship class where applicable; cosmetic zones; distortion limits; and required leak, strength, penetrant, or dimensional tests. Welding-procedure or personnel qualifications must be requested and verified before quotation rather than assumed.

Answer owner: PiPrecision Engineering Team

Achievable tolerance depends on the feature type and size, datum scheme, material and condition, geometry, process sequence, surface finish, and measurement method. Individual size features may be reviewed for bilateral tolerances down to ±0.005 mm, but this is not a default general tolerance and does not describe position, profile, flatness, runout, or other geometric controls. Apply ISO 2768 or another general-tolerance standard only by explicit drawing reference. PiPrecision confirms each critical requirement and its inspection method during drawing review.

Answer owner: PiPrecision Engineering Team

Project-specific options may include dimensional results, CMM reports for suitable features, first-article inspection, a certificate of conformity, and supplier or mill material certificates. These documents are not interchangeable: define the required format, governing standard or customer template, sampling level, traceability depth, and record language in the RFQ. AS9102 or another prescribed first-article format is supplied only when explicitly agreed. PiPrecision confirms document availability, scope, cost, and timing before production.

Answer owner: PiPrecision Quality Team

Thin walls may be feasible, but wall thickness alone does not predict stability. Material condition and residual stress, wall height and unsupported length, stock shape, tool pressure, heat, workholding, and removal sequence all matter. Engineering may recommend balanced roughing, intermediate stress relief, temporary supports, sacrificial features, revised corner radii or tolerances, or an agreed restrained-versus-free-state inspection method. Submit the full geometry rather than relying on a generic minimum-wall figure.

Answer owner: PiPrecision Engineering Team

Coaxial function should be defined with an appropriate datum reference and a current GD&T control such as position, circular runout, or total runout rather than an ambiguous note. Setup count, datum transfer, chucking, stock condition, tool pressure, part stiffness, and any post-machining process all affect the result. Engineering may keep related features in one setup, use qualified soft jaws or sub-spindle transfer, leave stock for grinding, and select a measurement method that matches the actual callout.

Answer owner: PiPrecision Engineering Team

Inspection is feature-specific. Diameters and bores may use micrometers, limit gauges, or bore gauges; form and runout may require a roundness instrument, indicator setup, or suitable CMM strategy; small profiles may use optical measurement; threads require the agreed gauges or measurement method; and surface texture requires a specified parameter and cutoff. CMM is not automatically the best method for every diameter, thread, or form tolerance. Identify datums, critical features, sampling, and reporting requirements before production.

Answer owner: PiPrecision Quality Team

Yes. Plating and powder coating generally add measurable material, while anodizing consumes some aluminum and builds some coating above the original surface; stripping, blasting, polishing, and etching may remove or alter the substrate. Nominal coating thickness does not always equal dimensional growth on a diameter or across two coated faces. Identify dimensions that apply before and after finish, coating thickness and tolerance, masking, thread-gauge state, and inspection stage so machining allowance and acceptance can be planned.

Answer owner: PiPrecision Engineering Team

A process can be controlled to an agreed reference, but an exact visual match is not normally guaranteed without defined acceptance criteria. Alloy and temper, lot, machining marks, blast media, surface preparation, geometry, rack location, coating thickness, dye or powder lot, sealing, gloss, texture, and lighting can all change appearance. For cosmetic work, provide an approved physical limit sample or defined color and gloss standard, identify cosmetic surfaces, and agree viewing conditions, defect limits, lot-to-lot expectations, and any instrumental color tolerance before production.

Answer owner: PiPrecision Quality Team

Formed dimensions vary with actual material thickness, alloy and temper, grain direction, inside radius, V-die and punch, bend method, springback, bend sequence, and measurement setup. Dimension critical features from functional datums and identify whether dimensions apply before or after forming and finishing. Avoid stacking tight tolerances across several bends without functional need. Engineering may recommend reliefs, revised radii or tolerances, tooling trials, first-off approval, or a checking fixture for repeat production.

Answer owner: PiPrecision Engineering Team

There is no single minimum order quantity for every project. PiPrecision can evaluate one-off prototypes as well as repeat production, but a practical minimum purchase or batch quantity may apply to raw material, special tooling, heat treatment, finishing, testing, or certification. Setup, programming, fixturing, inspection, and outside-process costs also affect the economical quantity. Request quantity breaks if you want to compare prototype and production pricing.

Answer owner: PiPrecision Engineering Team

PiPrecision targets an initial completeness and feasibility review within 24 hours for a complete RFQ. A firm quotation may take longer when clarifications, material pricing, special-process quotations, or inspection planning are required. Production lead time begins from the agreed commercial trigger stated in the quotation, such as order acceptance, deposit, or final drawing approval, and depends on material, complexity, quantity, tooling, inspection, finishing, and capacity. Use only the committed dates on the quotation or order confirmation for planning.

Answer owner: PiPrecision Engineering Team

PiPrecision can review a mutual or customer-supplied non-disclosure agreement before detailed project files are shared. Tell the commercial team that an NDA is required and wait for written execution before sending confidential files. An NDA does not by itself authorize the transfer of export-controlled, defense-controlled, personal, or otherwise regulated data; disclose those restrictions first so legal eligibility, permitted recipients, storage, and transfer method can be confirmed.

Answer owner: PiPrecision Content Team

PiPrecision can arrange international shipment using the method and named destination agreed on the order. The quotation should identify the applicable Incoterms rule and named place, freight responsibility, packaging, and required commercial documents. Transit and customs-clearance time are separate from production lead time. Before shipment, confirm the importer of record, broker instructions, tariff-classification responsibilities, country-of-origin requirements, and any controlled-goods or special-packaging obligations.

Answer owner: PiPrecision Content Team