Wholesale Price Custom CNC Machining Services: A Buyer's Guide

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  Key takeaways
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  Where the Money Goes at Each Batch Size
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  How to Compare Two Quotes Line by Line
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  Why Wholesale Price Custom CNC Machining Services Cost Less Per Part
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  Part Features That Move the Unit Price
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  Matching Tolerance and Inspection to the Function
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  Judging a Supplier Before You Send the PO
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  Material Choice and What It Does to the Batch
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  Lead Time, Batch Size and the Real Bottleneck
• 10
  Step by Step: From RFQ to Batch Delivery

A machined part carries two kinds of cost. Fixed cost is paid once: reading the drawing, writing the CAM program, building the fixture, proving the first article. Variable cost is paid on every part: material, cycle time, tool wear, deburring, inspection. In a one-off job the fixed cost lands on that single part. In a batch run it is divided by hundreds or thousands, and that division is the whole reason wholesale pricing exists.

The break point is not a round number. It depends on how much fixturing the part needs. A simple bracket on soft jaws may amortize in 20 pieces because the setup is an hour. A housing with six setups and a custom tombstone may not pay back until 200 pieces, because the fixture itself consumed two days of toolroom time.

So when a supplier quotes a lower unit price at 500 pieces than at 50, that is not a discount. It is the same job with the fixed block divided differently. Ask for the fixed and variable split and the quote becomes readable rather than a single number you either accept or argue about.

Material is the other half of the variable cost, and it does not scale linearly. Buying 6061-T6 plate for 20 parts means paying a cut fee and shipping on a small order. Buying for 2,000 parts means buying mill quantities, but also paying to store and handle them. The shop that quotes both sizes should tell you which stock form it assumed.

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  Fixed blockProgramming, fixture, first-article inspection. Paid once per part number, not per order.
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  Variable blockMaterial, cycle time, tooling consumption, finishing, inspection per piece.
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  The crossoverThe batch size where fixed cost per part drops below the variable cost of machine time.

Most of the unit price is decided before the quote is written, in the drawing. A wall that is 1.5 mm thick instead of 3 mm forces light passes and a smaller cutter, so cycle time climbs even though less material is removed. Deep pockets narrower than four times the cutter diameter need long-reach tooling that deflects, which means slower feed and more spring passes.

A single blanket tolerance note is the most common cost driver we see. Marking the whole drawing ±0.005 mm means every feature is inspected to that band, including a clearance hole that could run ±0.1 mm without consequence. Put the tight tolerance on the bearing bore, the mating face and the dowel holes. Let the rest run general tolerance.

Undercuts, cross-drilled holes that intersect at an angle, and threads that break into a curved surface all add operations. Each one may need a second setup or a hand operation at the bench. That is time, and time is the line item that grows fastest.

Surface finish follows the same logic. Ra 0.8–1.6 μm comes off the machine with a normal finishing pass. Ra 0.2–0.8 μm usually needs a finer stepover, a different insert, or a polishing operation after machining. Specify the finish only on the sealing face or the sliding surface, and leave the rest as machined at Ra 1.6–3.2 μm.

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  Thin wallsBelow about 1.5 mm on aluminium, chatter and distortion drive extra passes.
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  Deep, narrow pocketsDepth over 4× cutter diameter needs long-reach tooling and slower feed.
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  Blanket toleranceOne global tolerance note turns every feature into an inspection point.
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  Extra setupsEach new face that must be reached adds a fixture and a position error source.

±0.005 mm is achievable, but it should be reserved for features where the assembly depends on it. On a 4,000 mm long part, that tolerance also requires temperature control and a stable setup, because the material moves with heat. On a 30 mm bore it is routine. Same number, very different cost.

Inspection scope belongs in the quote. A shop that checks 100% of parts before shipment is doing something different from one that checks a sample. Raw material verification, in-process monitoring and a final dimensional report are three separate activities. If your assembly is regulated, ask which of them is included and whether the report is a first-article report or a full dimensional layout.

For medical and automotive work, the certification list narrows the field quickly. ISO 9001:2015 covers general quality management. IATF 16949:2016 adds automotive process controls. ISO 13485:2016 is the medical device route. ISO 27001:2022 covers information security, which matters when you send CAD files and BOMs to an outside shop.

A qualification rate of 99.99% sounds like a marketing number until you ask what it measures. Ask instead: what happens to a non-conforming part, and do we get to see the inspection data for our batch.

Start with the machine list. The machine list tells you what kind of work the shop can hold. 16 simultaneous 5-axis centers with a Ø400 mm rotary table handle complex geometry in one setup. 16 mill-turn centers handle round parts with cross features without a second fixture. 27 three-axis machines handle flat plates and simple housings efficiently. If the shop has no mill-turn capacity and your part is a shaft with cross holes, it will be quoted as two operations.

Second, ask about the largest part they run. A shop that routinely machines up to 4,000 mm has the crane, the floor space and the thermal stability for large work. A shop that tops out at 600 mm will struggle with a 1,200 mm frame even if the drawing looks simple.

Third, check where the parts are made. GreatLight runs three wholly-owned plants and a Singapore factory at No.3 Joo Koon Circle, Singapore 629032, alongside the Dongguan operation. For buyers who need an ASEAN origin or a second shipping lane, that matters more than a small price difference.

Fourth, ask how they handle your data. Uploads should be secure and confidential, and an NDA should be available on request before you send production drawings. A shop with ISO 27001:2022 has a documented process for this, not just a promise in an email.

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  Machine mix5-axis, mill-turn and 3-axis capacity determine how many setups your part needs.
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  Size envelopeMaximum processing size is 4,000 mm. Confirm your part fits with workholding.
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  Plant footprintThree wholly-owned plants, 7,600 m² total, plus the Singapore factory.
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  Data handlingNDA on request and secure uploads before drawings leave your network.

Aluminium is the default for batch work because it machines fast and stock is easy to get in bar, plate and extrusion. 6061-T6 is the general-purpose grade. 7075 and 2024 give higher strength but cut slower and cost more. ADC12 is a die-casting alloy, so it belongs in a different process route unless you are machining a casting.

Stainless is where cycle time jumps. 303 machines freely and is the right choice if corrosion resistance is moderate and you want speed. 304 and 316 work-harden, so feeds and speeds need to stay aggressive and the tool cannot dwell. 17-4PH (SUS630) can be machined in the annealed condition and then aged, which is often cheaper than machining it hard.

Titanium and Inconel are a different category. TC4 (Ti-6Al-4V) has low thermal conductivity, so heat goes into the tool, not the chip. Tool life drops, cutting speed drops, and the batch cost rises accordingly. Inconel is worse. If your part is aerospace or medical and the alloy is fixed by specification, budget for it rather than shopping for a cheaper shop.

Plastics are not automatically cheap. PEEK and carbon fibre are expensive per kilogram and abrasive on tooling. POM and ABS machine cleanly and hold tolerance well. For a plastic housing, it is often worth checking whether vacuum casting or 3D printing beats machining at your batch size.

A quotation and free DFM analysis within 12 hours is the front end. Production can start within 24 hours once the drawing is released and material is in stock. Parts ship in 3–5 days for typical jobs. Those numbers assume the drawing is final and the material is standard.

The bottleneck at batch size is rarely the spindle. It is material availability and finishing. A standard 6061 bar is on the shelf. A specific 17-4PH condition or a titanium grade may need to be ordered, and that lead time belongs to the mill, not the machine shop. Anodizing and plating are usually outside processes, so they add days even when the machining is done.

If your schedule is tight, split the order. Run the first 10% to prove the process and start assembly, then release the balance. This is normal for wholesale runs and it converts a single long lead time into two shorter ones.

Historical late-delivery probability below 2% is a useful figure, but ask what counts as late. The clock should start when the final drawing and PO are both confirmed, not when you first sent an inquiry.