CNC Machining Montreal: How Tolerance and Setup Really Work

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  What tolerance actually means on a machined part
• 2
  Why 5-axis setups hold tight tolerances more easily
• 3
  Material behavior changes the achievable number
• 4
  What we check before quoting a Montreal project
• 5
  Certifications, traceability and what they cover
• 6
  When to choose 3-axis, 4-axis or 5-axis

Tolerance is not one number. It is the stack of errors a part picks up from the blank, the fixture, the spindle, the tool, the temperature and the CMM itself. A shop that quotes ±0.005 mm is claiming it can control all six at once. That claim is only useful if you know which features it applies to.

Take a 6061-T6 aluminum housing with a Ø40 mm bore. The bore can hold ±0.005 mm because it is cut in one continuous pass on a stable setup. The bolt-hole pattern on the same part may only need ±0.1 mm, and the outer profile ±0.05 mm. Tightening every dimension to ±0.005 mm raises cost without adding function.

This is where a reasonable CNC machining Montreal quote gets built. The engineer reads your drawing, sorts critical fits from clearance holes, and assigns machining effort where it matters. When every callout is equally tight, the shop has to assume the worst and price the whole part like a gauge.

Surface finish follows the same logic. Ra 0.8–1.6 μm is a normal as-machined result on aluminum and steel. Ra 0.2–0.8 μm needs slower feed rates, sharper tooling or a finishing pass, and it adds time. Ask for fine finish only on sealing faces, bearing bores and sliding surfaces.

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  Tolerance is a stackBlank, fixture, spindle, tool, temperature, metrology.
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  Assign per featureA ±0.005 mm bore and a ±0.1 mm bolt hole are not the same job.
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  Finish is a cost leverRa 0.2–0.8 μm is a second operation, not a default.

Every time a part moves to a new fixture, it picks up a new datum error. On a 3-axis job with features on five faces, that might mean four or five setups. Each one adds 10–30 μm of positional drift if the fixture is not perfectly re-established.

A simultaneous 5-axis center keeps the part in one clamp and tilts the tool or the rotary table instead. With a Ø400 mm rotary table and 16 simultaneous 5-axis centers in our shop, we machine angled holes, blended radii and undercut pockets without re-fixturing. That removes most of the setup stack.

The mechanical limit is reach and stiffness. A long thin tool holder at full tilt deflects more than a short rigid one, so deep bores still need care. The rule we use: if the tool overhang exceeds four times its diameter, expect to slow down and take lighter cuts.

Part size decides the machine. Our 5-axis travel covers 4,000 × 400 × 150 mm for long parts. A 750 × 1,150 × 550 mm envelope handles most manifolds and plates, while 500 × 500 × 450 mm suits compact housings. If your part fits a 3-axis envelope, 3-axis is usually cheaper and just as accurate.

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  Fewer setups, less driftOne clamp beats four re-fixturings.
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  Reach is the limitTool overhang beyond 4× diameter hurts rigidity.
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  Match part to envelope3-axis for prismatic parts, 5-axis for angled features.

Aluminum 6061-T6 and 7075 cut clean and hold ±0.005 mm on stable features. The catch is heat. Aluminum expands about 23 μm per meter per °C, so a part machined warm and measured cold can read 30–40 μm off on a 1,500 mm length. We let long parts stabilize before final inspection.

Stainless 304 and 316L work-harden under a dull tool. Once the surface hardens, the next pass rubs instead of cutting, and finish drops fast. Sharp carbide, generous coolant and a consistent feed per tooth keep 17-4PH and 316L inside ±0.01 mm with Ra 0.8–1.6 μm.

Titanium TC4 (Ti-6Al-4V) and Inconel are the slow end. Low thermal conductivity pushes heat into the cutting edge, so speeds drop and tool life shortens. These parts are machined on 5-axis centers with high-pressure coolant, and cycle times can run three to five times aluminum for the same geometry.

Plastics behave differently again. POM and PEEK move with temperature and clamp pressure, so light clamping and sharp single-flute tooling matter more than spindle speed. Carbon fiber is abrasive and needs diamond-coated tools to avoid delamination at the edges.

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  Thermal growthAluminum moves 23 μm/m per °C.
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  Work hardeningDull tools ruin 304 and 316L finish.
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  Heat stays in the cutTi and Inconel need slower speeds, more coolant.

The first pass is a DFM read, not a price. We look at wall thickness, corner radii, tool reach and datum structure. A 2 mm deep pocket with a 1 mm internal corner needs a 1 mm cutter, which limits depth to about 3× diameter before it deflects. If the drawing asks for 10 mm depth, we flag it.

The second pass is tolerance allocation. If a bearing bore is ±0.005 mm and the mating plate is ±0.2 mm, we check whether the fit still works at the extremes. Often the fix is to loosen one callout, not to tighten both.

The third pass is inspection planning. A ±0.005 mm feature needs a CMM with a known uncertainty budget, and it needs a stable temperature. We inspect 100% of parts before shipment and can supply raw material checks, in-process monitoring and final reports on request.

Quote and free DFM analysis come back within 12 hours. Production can start within 24 hours, and parts usually ship in 3–5 days. Nothing here depends on a minimum order quantity. One prototype and a 10,000-part run go through the same review.

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  DFM firstCorner radii and tool reach decide feasibility.
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  Check the fit stackA tight bore next to a loose plate is wasted cost.
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  Plan metrology earlyTight features need CMM and stable temperature.

ISO 9001:2015 covers the general quality system: document control, corrective action, calibration, supplier control. IATF 16949:2016 adds the automotive layer, including PPAP-style documentation and stricter change control. ISO 13485:2016 applies the same discipline to medical devices, where process validation and traceability are audited.

ISO 27001:2022 covers information security. For a Montreal customer sending CAD files, that matters more than it sounds. Uploads are handled as confidential, access is limited to the project team, and we sign an NDA on request before drawings move.

Traceability runs from the material certificate to the finished part. We keep heat numbers tied to the job, record the machine and program revision, and log inspection results. If a batch is questioned two years later, we can pull the record.

Accuracy claims are only as good as the measurement behind them. A tolerance of ±0.005 mm is checked with calibrated equipment under controlled temperature, not with a hand caliper on the shop floor. If a report is required, say so at quote time so the inspection plan includes it.

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  Four certificatesISO 9001, IATF 16949, ISO 13485, ISO 27001.
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  Traceable recordsHeat number, program revision, inspection log.
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  NDA on requestSigned before drawings are shared.