Cut CNC processing costs without giving up tolerance

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  Key takeaways
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  What actually drives the unit price
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  Part design: what you can change before you ask for a discount
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  Material choice: the line item that moves fastest
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  Quantity and production strategy: where the break points sit
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  Five-axis machining: when it lowers the price and when it does not
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  Reading a quote: the terms that hide the real price
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  Seven steps to cut CNC processing costs on your next order

Most of the price is set before the shop turns on a spindle. Deep pockets, thin walls and features that can only be reached from one direction force extra setups and extra handling. If a wall is 0.8 mm thick on a 100 mm long aluminium part, the machinist has to take light passes and often add a support fixture. That is time you pay for.

Go through the drawing and ask which faces are functional. A bolt boss needs a flat face and a true hole. A cosmetic side panel needs neither. Marking every face with the same tolerance forces the shop to machine every face in the same operation, and that usually means more setups, not fewer.

Corner radii are another quiet cost. A pocket with a 3 mm internal radius needs a small cutter, and small cutters run at lower feed rates and break more often. Widening that radius to 6 mm or 8 mm, if the part allows it, can cut cycle time noticeably without touching the function.

The cheapest design change is usually the one that lets a part be made in one orientation. When a single 5-axis setup can reach five sides, you remove the re-fixturing step entirely, and with it the re-datum error that drives scrap.

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  Reduce setupsGroup features so they can be reached from one or two directions.
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  Loosen non-functional tolerancesGeneral ±0.05 mm is fine for clearance holes and cosmetic faces.
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  Open corner radiiUse the largest internal radius the part allows to keep cutters rigid.
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  Avoid thin floorsUnder 1 mm on aluminium invites chatter and rework.

Material is often the single largest line on a machining quote, and it is the one buyers can change without redesigning anything. Free-machining grades exist for a reason. 303 stainless machines roughly twice as fast as 304 and gives a better finish, so it is the default for shafts and fittings that will not be welded. If the part needs welding or corrosion resistance in a chloride environment, you accept the slower cut and pay for 304 or 316L.

Aluminium behaves the same way. 6061-T6 is the workhorse: good strength, good finish, widely stocked. 7075 offers roughly twice the yield strength but cuts slower and costs more per kilogram. Unless the part is a stressed bracket or a high-load fixture, 7075 is usually money spent on a property the part never uses.

Titanium and Inconel sit at the far end. Ti-6Al-4V has low thermal conductivity, so heat stays in the cutting zone and tools wear fast. Inconel is worse. For these alloys the machining time can exceed the material cost, which means design changes that reduce removed volume matter more than shopping for a cheaper mill.

One practical check: ask the shop what stock size it plans to buy. If your part fits a standard plate or bar size with little waste, you save on both material and roughing time. A part that is 3 mm over a standard size can cost several times more in stock than the finished geometry suggests.

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  303 vs 304Free-machining grade for non-welded parts; 304 when corrosion or welding matters.
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  6061 vs 70756061 covers most brackets and housings. Use 7075 only where load demands it.
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  Near-net stockPick a geometry that fits a standard bar or plate size to cut roughing time.

CNC pricing is not linear. The first piece carries the programming, fixturing and setup. The tenth piece carries almost none of it. That is why the gap between 1 and 10 is large, the gap between 10 and 100 is moderate, and the gap between 100 and 1,000 is smaller than most buyers expect.

For quantities in the low hundreds, a single 5-axis machine with a tombstone fixture can run several parts per cycle. That is where most of the savings sit for housing-type parts. Above roughly 1,000 pieces, it is worth comparing machining against die casting or vacuum casting, especially if the geometry is not changing. Tooling cost is real, but so is a 20-minute cycle repeated a thousand times.

Batching matters too. If you order 200 pieces now and 200 in three months, the shop may keep the fixture and re-run the same program, which is cheaper than a fresh setup. If you know the second order is coming, say so at the quoting stage.

Inspection strategy scales with quantity as well. First-article inspection on a new program is standard. Full dimensional reports on every piece in a 5,000-piece run add cost that most programs do not need. Ask for a sampling plan instead and specify which dimensions are critical.

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  1–10 piecesSetup dominates. Expect the highest unit price here.
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  50–500 piecesBest balance for machined parts; fixtures are amortized.
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  1,000+ piecesCompare against die casting or vacuum casting before committing.

Five-axis gets sold as a precision upgrade, but its real value on cost is setup reduction. A part with features on five sides that would need three or four fixtures on a 3-axis machine can often be finished in one or two setups on a simultaneous 5-axis center. Each setup you remove takes with it a fixture, a re-datum operation and a scrap risk.

The catch is cycle time on simple geometry. A flat plate with holes drilled from one direction runs faster on a 3-axis machine because the machine does not spend time orienting the table. If the part is prismatic and simple, 5-axis adds cost, not savings.

The rule we use on the floor: count the number of distinct tool approach directions on the drawing. Two or fewer, and a 3-axis or 4-axis machine is usually cheaper. Three or more, and 5-axis tends to win once you include fixtures and handling.

Complex curved surfaces, impellers, medical implants and angled ports are the clear cases. So are parts where a single datum matters, because fewer setups mean fewer chances to stack error. That is a quality argument as much as a cost one.

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  Count approach directionsTwo or fewer: 3-axis. Three or more: check 5-axis pricing.
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  Watch simple prismatic partsTable orientation time can make 5-axis more expensive.
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  Fewer setups, fewer datumsSetup reduction also lowers scrap and inspection load.

Two quotes for the same drawing can differ by 40% and neither shop is lying. The difference is usually scope. One price includes material, machining, deburring, anodizing, inspection and freight. The other is machining only, with the finish quoted separately. Compare the delivered part, not the machining line.

Ask what happens when a dimension is out. A shop that inspects 100% before shipment and supplies reports on request will catch a bad part before it ships. A shop that samples may not. The cost of a rejected lot at your assembly line is far higher than the few percent you saved on the unit price.

Certifications are a scope item too. If your part goes into a vehicle, a medical device or a regulated electronics product, the shop needs the relevant quality system in place. ISO 9001:2015 covers general quality management. IATF 16949:2016 applies to automotive production. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters when you are sending unreleased CAD files to an overseas supplier.

Finally, ask how long the quote is valid and what the payment terms are. A price held for 30 days is not the same as one held for six months in a moving metal market. Neither is better in the abstract, but you should know which one you are signing.

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  Match the scopeMachining only vs turnkey with finish, inspection and freight.
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  Ask about inspection100% inspection before shipment, reports on request.
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  Check the quality systemISO 9001, IATF 16949, ISO 13485, ISO 27001 depending on your industry.