UK CNC Processing Cost: A Buyer's Guide for Engineers

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  Key takeaways
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  Which sourcing route fits which job
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  What actually makes up UK CNC processing cost
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  Where engineers can still cut the number
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  How to compare quotes that look nothing alike
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  Batch size, freight and the hidden cost of splitting work
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  Six steps to a quote you can defend

A quoted unit price is the sum of five things: material, machine time, setup, finishing and inspection. Material is the easiest to see and usually the smallest share on a small aluminium part. Machine time is the largest, and it is set by the geometry you drew, not by the supplier's goodwill. Setup is charged once per order and per operation, so its weight depends entirely on batch size.

On a 5-off order of a milled bracket, setup and programming can take more hours than cutting. On a 500-off run with a soft jaw fixture, the same setup is spread across 500 parts and becomes almost invisible. That is why the same drawing produces quotes that differ by a factor of three. The suppliers are not disagreeing about quality. They are pricing different assumptions about fixtures and batch size.

Finishing and inspection are the two lines buyers most often misread. Anodising is priced per batch with a minimum charge, so a 20-part order can carry the same finishing cost as a 200-part order. Inspection is priced in hours, and a ±0.005 mm callout with a full dimensional report can add more time than the machining itself. Ask for these as separate lines.

One more driver sits outside the machining shop: how the supplier buys material. A stockist with 6082 plate on the shelf ships in a day. A mill order for 7075 in a non-standard thickness adds weeks and a cut charge. Material availability quietly moves both the price and the date.

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  MaterialGrade, form and thickness availability move the price more than the alloy name.
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  Machine timeSet by feature count, depth-to-diameter ratio and tolerance, not by part weight.
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  SetupCharged per operation per order; falls fast as quantity rises.
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  Finishing and inspectionBatch-priced. Always ask for them as separate lines.

Most of the cost is fixed by the time the drawing leaves your desk. The cheapest change is depth-to-diameter ratio. A pocket 4 mm wide and 40 mm deep needs a long, slender cutter run at reduced feed, and it will chatter. Widen it to 8 mm or split it into two pockets and the cycle time drops sharply.

Corner radii are the second lever. An internal corner must be cut with a tool that fits it, so an R2 corner forces a smaller cutter and slower passes everywhere in that pocket. Matching the corner radius to a standard cutter diameter you can actually buy keeps the whole operation on a stiffer tool. The same applies to floor fillets: a sharp internal floor needs a special tool, a 0.5 mm fillet does not.

Tolerance is the third. A ±0.005 mm callout on every dimension of a bracket is usually unnecessary. Put the tight tolerance only on the features that locate or seal, and mark the rest as general tolerance. This lets the machinist take a heavier first pass and check fewer points. The saving is real and it does not touch function.

Finally, finish. Ra 0.2–0.8 μm on a non-sealing surface means slow finishing passes and extra polishing. Ra 1.6–3.2 μm as machined is fine for most brackets, covers and housings. Keep the fine finish for sealing faces, bearing seats and sliding surfaces.

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  Pocket depthKeep depth under 4× the cutter diameter where you can.
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  Corner radiusMatch internal radii to a standard cutter size.
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  Tolerance mapTight on locating features, general everywhere else.
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  Finish specRa 1.6–3.2 μm as machined covers most non-sealing faces.

Two quotes for the same part are rarely the same offer. Before comparing the number at the bottom, check four things: is material included, is finishing included, is inspection included, and is there an NRE or programming line. A quote that looks 20 percent cheaper often simply excludes anodising or the first-article report.

Delivery date is the next trap. A short date on a quote is not a commitment. Ask what the date assumes about material availability and whether it starts from PO or from drawing approval. On the manufacturing side, GreatLight returns a quotation and DFM analysis within 12 hours and can start production within 24 hours, with parts shipping in 3–5 days. That is worth comparing against a UK shop quoting three weeks, but only if the part and the report scope match.

Certification scope matters if your part goes into a regulated product. ISO 9001:2015 covers general quality management, IATF 16949:2016 is the automotive standard, ISO 13485:2016 is for medical devices, and ISO 27001:2022 covers information security. If your data is sensitive, the last one matters as much as the first.

Then check the batch assumption. A price quoted at 100 pieces is not valid at 10. Ask for a small quantity break table: 1, 10, 100 and 1,000 pieces. A supplier who will not give you that table is guessing, and their number will move after the PO.

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  Scope linesMaterial, finishing, inspection and NRE shown separately.
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  Date basisDoes the lead time start at PO or at drawing approval?
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  CertificatesMatch the standard to the industry your part serves.
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  Quantity tableAsk for 1 / 10 / 100 / 1,000 piece pricing.

Batch size is the strongest lever on UK CNC processing cost, but it has a ceiling. Above a few thousand pieces, a casting or a die-cast tool often beats machining on unit price, though it adds tool cost and a fixed lead time. Below that, machining stays flexible and lets you change the design between runs. No minimum order quantity helps here: a run can start from one prototype and scale to 10,000+ parts without requoting the whole approach.

Freight and duty are part of the landed cost and are easy to forget when comparing a domestic quote with an overseas one. Air freight on a small, dense part is cheap per kilogram but has a minimum charge. Sea freight is cheaper per kilogram but adds weeks. For anything under about 50 kg, air usually wins on total cost once you count the cash tied up in transit stock.

Splitting work across two suppliers is the most common hidden cost. One shop machines the part, another anodises it, and a third does the laser marking. Each handover adds handling, a queue and a new chance for a scratch. Keeping machining, finishing and laser marking under one roof removes those handovers. Laser marking has its own limit worth knowing early: minimum character height is 1.5 mm, so a 0.8 mm part number will not reproduce.

Packaging matters on finished parts. Anodised and polished surfaces scratch in transit. Ask how parts are separated before you approve a soft-finish cosmetic part, because a rejected finish is a full remanufacture, not a touch-up.

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  Batch ceilingPast a few thousand parts, casting usually wins on unit price.
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  Freight modeAir for small dense parts, sea for heavy slow-moving stock.
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  One roofMachining, finishing and marking in one shop removes handovers.
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  PackagingAsk about part separation before approving a cosmetic finish.