Swiss CNC Machining Service: How to Judge One Before You Send an RFQ

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  Six things to settle before you commit
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  Swiss turning vs. other processes: which one fits the part
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  What a Swiss CNC machining service actually does differently
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  Tolerance and surface finish: what to ask for, and what not to
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  Materials that turn well on a Swiss machine, and the ones that fight back
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  Judging a swiss cnc machining service: the answers that matter
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  Where the money goes on a small turned part
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  Step by step: preparing a Swiss turning RFQ that gets a usable quote

On a conventional lathe the part spins and the tool moves along it. On a Swiss-type machine the bar stock slides forward through a guide bush, and the tools sit within a few millimeters of that bush. The unsupported length of material is tiny, sometimes under 5 mm. That single change is why a Ø2 mm shaft at 40 mm long can be turned without bowing away from the tool.

The guide bush also sets the practical limit. Standard bushes are sized to the bar. If your stock varies more than about 0.01 mm in diameter, the bar either seizes or slips, and the shop has to switch to a pick-up or guide-bush-free setup. That switch changes the achievable tolerance and the cycle time, so it should be discussed at quoting, not after the first article.

Most Swiss machines run a main spindle and a sub-spindle. The main spindle machines the front; the sub-spindle picks up the parted-off part and works the back. Cross-drilling and slotting units sit on the gang slide. A part that needs a cross hole, a milled flat and a back chamfer can come off the machine finished in one cycle instead of three.

Cycle time is short because travel is short. The trade-off is setup. Tool changeover, bush sizing and cam or program proving take time, so Swiss work becomes economical once the run is long enough to spread that setup across the parts. For a handful of pieces, a mill-turn or 3-axis job is usually cheaper.

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  Guide bush supportThe closer the support to the cut, the smaller the deflection on slender diameters.
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  Sub-spindle back-workingRemoves a second operation on parts with features on both ends.
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  Bar size is the ceilingConfirm your largest diameter against the shop's bar feeder range.

Our general machining tolerance is ±0.005 mm. On a Swiss machine that figure is realistic on a diameter that is turned in one pass with a rigid setup. It is not realistic on a long unsupported section, on a thin wall, or on a feature cut with a tool that has to reach far from the guide bush.

Surface finish behaves the same way. A turned OD can reach Ra 0.2–0.8 μm with the right insert and feed. An as-machined cross hole sits closer to Ra 1.6–3.2 μm. If your drawing calls for Ra 0.4 μm inside a small bore, the shop will either add a reaming or honing step or tell you the tolerance is not cost-effective. Both answers are legitimate; a shop that simply says yes without asking is the one to question.

The useful habit is to tolerance only what the function needs. A shaft that locates in a bearing needs a tight diameter and a controlled roundness. The same shaft's free end does not. Tolerancing everything to the tightest number raises inspection time, scrap risk and price without improving the assembly.

Ask how the shop verifies. A CMM program written for the part, plus a first-article report, tells you whether the claimed tolerance is measured or just stated. We inspect 100% of parts before shipment and can supply reports on request.

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  Tight where it fitsReserve ±0.005 mm for mating diameters and functional faces.
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  Finish follows functionRa 0.2–0.8 μm on sealing or bearing surfaces; leave the rest as machined.
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  Inspection evidenceAsk for a first-article report and per-lot dimensional data.

Free-machining stainless such as 303 and 416 cuts cleanly at high spindle speeds, which is why it dominates small turned parts. 304 and 316 are tougher and work-harden if the feed stops in the cut, so the shop has to keep the tool moving. 17-4PH in the H1150 condition machines reasonably; in the annealed condition it is gummy and slow.

Aluminium is straightforward. 6061-T6, 2024 and 7075 all run well at high rpm, and the guide bush clearance is easy to hold because bar stock tolerance is good. Brass and copper alloys such as C36000 and C110 are among the easiest materials on a Swiss machine, though beryllium copper needs dust control and is usually quoted with that in mind.

Titanium and Inconel are the difficult end. Ti-6Al-4V has low thermal conductivity, so heat goes into the tool rather than the chip. Tool life drops, cycle time rises, and the price reflects it. These alloys are still machined on Swiss machines for aerospace and medical parts, but the run length should justify the tooling cost.

Plastics behave differently again. POM and PA are common for small bushings and insulators. PEEK holds dimension at temperature but is abrasive. Carbon fibre reinforced stock wears tools fast and needs carbide or diamond. If your part is a filled plastic, mention the filler percentage at quoting; it changes the tool and the feed.

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  Free-machining grades first303 and 416 stainless give the best cost per part on small diameters.
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  Work-hardening risk304 and 316 need constant feed; dwell marks become hard spots.
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  Filled plasticsState the filler type and percentage so tooling is chosen correctly.

Start with the machine list. A shop that runs Swiss-type lathes should be able to tell you the bar capacity, the number of axes, whether there is a sub-spindle, and how many live tools are on the gang slide. Vague answers usually mean the work is subcontracted, which adds a handoff and a second tolerance stack.

Next, certification scope. ISO 9001:2015 covers quality management generally. IATF 16949:2016 is what automotive programs ask for, and ISO 13485:2016 applies to medical device work. ISO 27001:2022 covers information security. A certificate is only useful if the process you are buying falls inside its scope, so ask which plants and which processes are covered.

Then the commercial terms. No minimum order quantity matters when you are prototyping, because you can test the shop on one piece before committing to a run. It should scale to 10,000+ parts without a process change. Ask whether the same machine family runs the prototype and the production order.

Finally, communication. Quotation and free DFM analysis within 12 hours is a reasonable baseline. If the shop flags a tolerance that will be hard to hold before you place the order, that is a good sign. If it accepts everything silently and the first article fails, you have lost a week.

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  Machine specificsBar capacity, axes, sub-spindle, live tool count.
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  Scope of certificationMatch the certificate to the process and plant doing your work.
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  Prototype-to-production pathConfirm the same process runs one piece and 10,000 pieces.

Setup is the first cost. Bar loading, bush sizing, tool presetting and program proving take hours regardless of order size. On a 500-piece run the setup might be a small share. On a 20-piece run it dominates. This is why very small quantities of Swiss parts often cost more per piece than a milled part, even though the cycle time is shorter.

Cycle time is the second cost, and it is driven by the longest single feature, not the average. A part with one deep cross hole may spend more time on that hole than on all the turning. If you can relocate that hole to a face that is easier to reach, or open the tolerance, the price drops quickly.

Material is the third. Bar stock is bought to a diameter, and the guide bush needs a specific tolerance. A free-machining grade in a standard bar size is cheap. A titanium bar in a non-standard diameter with a tight tolerance may carry a minimum buy and a lead time of its own.

Inspection is the fourth. A part with twelve toleranced features needs a CMM program and a longer inspection cycle. A part with four functional tolerances can be checked with micrometers and a comparator. Trimming the tolerance list is the most direct way to cut cost without touching the process.

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  Setup dominates small runsBelow a few hundred pieces, setup is the largest line item.
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  One slow feature sets the cycleA single deep hole or tight slot can define the whole cycle time.
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  Bar size affects material priceStandard diameters in free-machining grades are the cheapest route.