Accuracy of CNC Machining Experience With Our Chicago Facility
This page explains what our accuracy CNC machining experience means for real tolerances, surface finish and part geometry. It is written for engineers and buyers who need to judge whether a shop can hold a spec on a specific part. After reading, you can compare our capability numbers against your drawing and decide what to send.
What ±0.005 mm Actually Means on the Shop Floor
A tolerance callout is a starting point, not a promise. ±0.005 mm on a 6061 aluminium bracket with a 60 mm footprint behaves very differently from the same number on a 400 mm Inconel housing. Thermal growth, tool deflection and fixture stiffness all scale with part size and material hardness.
Our baseline is ±0.005 mm on features we can reach without repositioning the part. That means a single setup on a simultaneous 5-axis center, a rigid workholding plan, and a temperature-stable shop. When a feature needs a second setup, we bracket the tolerance rather than the geometry.
We do not quote a blanket tolerance for every dimension on a drawing. We quote per feature. If your drawing has a mix of loose and tight callouts, send it as-is and we will mark which ones sit inside our normal band.
- 1Aluminium 6061 / 7075Holds ±0.005 mm on features under 150 mm with a single setup.
- 2Stainless 17-4PH / 316LHolds ±0.005 mm; allow extra passes for work hardening.
- 3Titanium TC4 / InconelTighter callouts need slower feeds and more in-process checks.
- 4Thin walls under 1 mmTolerance depends on support; we review the fixturing first.
How 5-Axis Work Reduces Accumulated Error
Every time a part changes setup, you add a small error stack: fixture locating, datum pickup, and machine positioning. On a 4-axis or 3-axis mill, a complex part may need four or five setups. That stack often eats more tolerance than the cut itself.
Simultaneous 5-axis cutting keeps more of the part in one setup. We run 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. The choice is driven by geometry, not by which machine is free.
A rotary table of Ø400 mm lets us index around a part without re-clamping. For a hydraulic manifold with ports on five faces, that single decision removes three setups and the error that comes with them.
Short parts, simple parts. Sometimes a 3-axis machine with a good vise is the more accurate answer, because there is less motion to control. We pick the process that holds the feature, not the most expensive machine.
Machine and Travel Limits by Part Size
Match your envelope and feature count to the right machine class before you request a quote.
| Machine class | Typical travel | Best for |
|---|---|---|
| 5-axis simultaneous | 500 × 500 × 450 mm | Complex geometry, 3+ faces, tight true position |
| 5-axis simultaneous | 600 × 600 × 600 mm | Mid-size housings, angled ports, undercuts |
| 5-axis simultaneous | 750 × 1,150 × 550 mm | Large plates and frames with mixed features |
| Mill-turn | Ø400 mm rotary table | Shafts, bushings, parts needing turning plus milling |
| 3-axis / 4-axis | Up to 4,000 × 400 × 150 mm | Long rails, simple prismatic parts, single-face work |
How We Verify Accuracy Before Parts Ship
Accuracy that is not measured is a guess. We inspect 100% of parts before shipment, and the checks start before the first cut. Incoming bar stock is verified for grade and condition, because a substituted alloy can move differently after machining.
During the run, operators monitor critical features against the drawing. When a dimension drifts, we correct the offset rather than running the rest of the batch and sorting later. That keeps the process stable instead of reactive.
Final inspection confirms the features your drawing calls out. Reports are available on request, including dimensional results for the features we agreed to check. For regulated programs, that report becomes part of your device or PPAP file.
Our historical qualification rate is 99.99%, and the late-delivery probability is below 2%. Those numbers come from our own production records, not from a customer survey.
Finishing Steps That Do Not Ruin the Tolerance
A part can leave the machine in tolerance and come back out of tolerance after finishing. Anodizing builds a coating on every surface, and hardcoat can shift a press-fit dimension. We plan the finishing sequence around the tolerances that matter.
For a bore that must stay within ±0.005 mm, we either mask it or leave stock and cut it after coating. For cosmetic surfaces, bead blasting and tumbling even out tool marks before anodizing. Both choices get decided at the DFM stage, not after the parts are coated.
We offer anodizing in clear, color, hardcoat and conductive types, plus electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing. Laser marking is available with a minimum character height of 1.5 mm.
- 1Tight bore plus anodizeMask the bore or machine it after coating.
- 2Cosmetic face plus bead blastBlast before anodize; blasting after can round edges.
- 3Hardcoat on threadsExpect growth; we cut threads to allow for it.
- 4Laser mark placementSend a DXF or step file with the mark position.
When a Tight-Tolerance Shop Is the Right Call
Not every part needs ±0.005 mm. A bracket that bolts to a welded frame usually does not. Paying for tight tolerance on a loose part adds cost without adding function.
Tight tolerance earns its place when parts mate with other parts, when a bore carries a bearing or a seal, when an optical or fluid path must align, or when the assembly cannot absorb variation. Aerospace, medical devices, robotics and EV drivetrain components are typical examples.
It is the wrong call when the interface is compliant, when the part will be re-machined on site, or when the drawing tolerance is looser than what our process naturally delivers. In those cases we say so and quote the looser band.
Tell us the function of the feature, not only the number. If a bore needs to hold a bearing, we may recommend a different fit class than the one on the print. That conversation usually saves both cost and assembly trouble.
Questions Engineers Ask Before Sending a Drawing
Can you hold ±0.005 mm on a part over 300 mm long?
It depends on the feature and the material. A single face or bore can hold that band. A long dimension across the whole part is harder because thermal and fixturing effects accumulate.
Send the drawing with a note on which dimensions are critical. We will tell you which ones we can hold and which ones need a different approach, such as a second op or a temperature-controlled check.
What surface finish comes standard?
As-machined surfaces typically land in the Ra 1.6–3.2 μm range. Where a drawing calls for finer, we target Ra 0.8–1.6 μm, and for sealing or optical faces we can reach Ra 0.2–0.8 μm with additional operations.
Finish and tolerance interact. A polished face often needs a separate pass, and that pass can change a dimension if it is not planned.
How do you handle a part that needs turning and milling?
Mill-turn centers cut both on one platform, which removes a setup and the error that comes with it. We run 16 mill-turn centers for shafts, bushings and parts with concentric features.
If the part is better split across two machines, we will say so. The goal is the feature, not the machine count.
Do you inspect every part or sample the batch?
We inspect 100% of parts before shipment. Incoming material, in-process features and final dimensions are all checked.
Inspection reports are available on request. Let us know which features you need documented and we will include them in the report.
What materials can you machine to tight tolerance?
Aluminium grades 6061, 7075 and 2024 are the most predictable. Stainless 303, 304, 316L and 17-4PH also hold tight bands with the right tooling.
Titanium TC4 and Inconel can hold the same tolerance but need slower cutting and more checks. Plastics like POM and PEEK move after machining, so we plan for stress relief.
How do I start a tight-tolerance job?
Upload the 3D model and 2D drawing through our quote page. We return a quotation and a free DFM analysis within 12 hours.
Production can start within 24 hours of approval, and parts ship in 3–5 days. Uploads are secure and confidential, and an NDA is available on request.
Send the Drawing. We Will Tell You What Holds.
Upload your model and drawing for a quotation and free DFM analysis within 12 hours. We will mark the critical features and flag anything that needs a different approach.
12-hour quote100% inspectionNDA on requestNo minimum order
