Cambridgeshire CNC Processing Professionals
This page explains what to check before you send a drawing to a CNC shop: axis count, tolerance class, material behavior, and inspection paperwork. It is written for design engineers, sourcing managers and lab teams in Cambridgeshire who buy machined metal and plastic parts. Read it and you can judge which parts fit which process, and when a quote should worry you.
How to read a CNC capability claim
Most quotes look the same on page one. The differences sit in setup count, spindle hours and inspection records.
Three-axis, four-axis or five-axis: pick by geometry
A three-axis machine moves the tool in X, Y and Z only. The part usually needs a new fixture for each face, and every refixture adds stack-up error. For brackets, plates, housings and manifolds with features on two or three faces, this is still the cheapest route. Tolerance of ±0.005 mm is reachable on a stable setup, but it depends on how many times you touch the part.
Four-axis adds rotation around one axis, normally A. The tool can reach around a cylinder or a shaft without a second op. Cam profiles, splined shafts and tubular parts with cross-drilled holes fit here well. What it cannot do is tilt the tool relative to the surface, so undercut walls and compound angles still need a second setup or a five-axis cut.
Five-axis adds two rotary axes on top of the linear travel. The tool can approach the workpiece from almost any direction in a single setup. That matters when a part has features on five or six faces, or when the wall is thin enough that refixturing would distort it. We run 16 simultaneous five-axis machining centers, with a Ø400 mm rotary table for parts that need continuous rotation.
Cases where fewer axes cost less and hold better
Five-axis is not automatically better. A flat plate with ten holes and a pocket on one face will be finished faster on a three-axis mill with a vise, and the price reflects that. Programming time on a simultaneous five-axis path is longer, and the post-processor has to be right or the surface finish shows chatter marks.
Simple turned parts belong on a lathe, not a mill. Shafts, bushings, spacers and fittings with rotational symmetry are cheaper on a mill-turn center or a CNC lathe. We keep 16 mill-turn centers for exactly this reason, so a part with a turned body and milled flats does not need two separate vendors.
Deep pockets with a small corner radius are also a poor fit for a long five-axis cycle. If the pocket depth is more than four times the cutter diameter, tool deflection grows and the shop has to slow down. A better design move is to open the corner radius or split the pocket into two depths.
Axis count vs. part geometry
Use this as a first filter before you ask for a quote.
| Part type | Best fit | Why |
|---|---|---|
| Flat plate, features on one face | 3-axis | One setup, vise or vacuum plate |
| Housing with four side faces | 4-axis | Rotary table indexes between faces |
| Impeller, bladed disk, complex contour | 5-axis simultaneous | Tool tilt avoids gouging and collisions |
| Shaft with milled flats | Mill-turn | Turning and milling in one cycle |
| Thin-wall aerospace bracket | 5-axis | Single setup limits distortion |
| Large frame up to 4,000 mm | 3-axis or gantry | Fits 4,000 × 400 × 150 mm travel |
What ±0.005 mm actually means in production
A tolerance of ±0.005 mm is a production limit, not a marketing number. It holds on features where the setup is rigid, the material is stable, and the temperature is controlled. It does not hold across a 500 mm aluminum frame if the shop machines it in a cold room in January and measures it in a warm inspection room. Thermal expansion of aluminum is roughly 23 μm per meter per degree Celsius, so a 5 °C swing across a 500 mm part moves the dimension about 58 μm.
Material choice changes the achievable surface finish. Aluminum 6061 and 7075 cut cleanly and reach Ra 0.2–0.8 μm with a good finishing pass. Stainless 316L work-hardens, so light passes and sharp tooling matter more than spindle speed. Titanium TC4 (Ti-6Al-4V) and Inconel need slower cutting speeds and more coolant, which raises cycle time and price. Plastics like PEEK and POM move after machining, so a shop that understands them will rough, stress-relieve, then finish.
We keep stock in aluminum 6061, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12; stainless 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH; steel 1018, 1045, 4130, 4140, 4340 and A36; and copper alloys including C101, C110 and C36000. If your drawing calls for a grade outside that list, say so early. Sourcing a new grade adds time before the first chip is cut.
What to ask for in an inspection report
A first-article inspection report should list the drawing revision, the measurement instrument, and the actual value for each critical dimension, not just a pass stamp. Calipers are fine for a general check, but a ±0.005 mm callout needs a CMM or a micrometer with a calibration certificate. Ask what instrument was used on the tight features.
In-process monitoring matters on long cycles. A five-axis cycle on a titanium impeller can run for hours, and a tool break halfway through wastes the blank. A shop that checks between operations catches the problem before the finishing pass. We do a raw material check on receipt, monitor during machining, and run a final inspection before shipment.
Certifications are a filter, not a guarantee. ISO 9001:2015 covers general quality systems. IATF 16949:2016 is required for automotive production parts. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters if your drawings are sensitive. Match the certificate to your industry before you assume a shop is qualified.
Questions engineers ask us
How fast can a Cambridgeshire team get a quote and a first part?
We return a quotation and a free DFM analysis within 12 hours of receiving a STEP file and a 2D drawing. Production can start within 24 hours after the quote is approved, and parts normally ship in 3–5 days. Complex five-axis work or an unusual material grade can take longer, and we will say so before you commit.
Historical late-delivery probability is below 2%, but that is a past figure, not a promise on your specific part.
Can you hold ±0.005 mm on a large part?
It depends on the feature and the material. We hold ±0.005 mm on stable setups and controlled temperature. On a 4,000 mm frame, the achievable tolerance is wider because thermal movement and machine geometry both grow with size. Send the drawing and we will tell you which dimensions are realistic and which need a different datum strategy.
What is the smallest order you accept?
There is no minimum order quantity. We run from one prototype to 10,000+ part runs. A single part is quoted on its own setup time, so the unit price is higher, but the tooling and programming carry over if the design goes into production.
Do you sign an NDA before I share drawings?
Yes. Uploads are secure and confidential, and an NDA is available on request before any file exchange. For defense, medical or unreleased consumer products, tell us at first contact so the right agreement is in place before the CAD goes out.
Can you do finishing as well as machining?
Yes. We handle anodizing in clear, colour, hardcoat and conductive types; electroless nickel, zinc, silver and gold plating; powder coating and black oxide; bead blasting, tumbling, brushing and polishing; and laser marking with a minimum character height of 1.5 mm. Keeping finishing in-house avoids a second shipping cycle between vendors.
Which file formats do you need for a quote?
STEP or IGES for the 3D model, plus a PDF or DXF drawing that carries tolerances, datums, surface finish callouts and material grade. If the drawing is incomplete, we will flag the gaps in the DFM note rather than guess. A native SolidWorks or Parasolid file helps but is not required.
Send a drawing, get a real answer
Upload your CAD and we will return a quote, a DFM note and a realistic tolerance assessment within 12 hours.
12-hour quote100% inspection before shipmentNDA on request
