CNC Turned Electrical Contacts
Connector pins · socket contacts · Cu-ETP · CuBe2 · phosphor bronze · Au / Ni / Ag · Ø0.8–12 mm
CHX Metal turns electrical contacts and connector pins from copper alloy bar on 70 Tsugami Swiss-type lathes and 50 CNC lathes, held to ±0.005 mm on the mating diameters, with selective gold, nickel or silver plating. Typical parts are board-to-board pins, circular connector solder cups, spring-loaded pogo barrels, busbar contacts and terminal studs. Monthly capacity on this family is in the millions of pieces, and a price with plating spec returns within 24 hours.
A contact is judged by three numbers that never appear on the drawing in the same place: contact resistance in milliohms, insertion force in newtons, and the number of mating cycles before the plating wears through. Everything else — base alloy, temper, underplate, gold thickness, chamfer, bore tolerance — is a way of buying those three numbers. This page is about the turning decisions that set them.
What the drawing has to pin down
Most contact drawings that arrive here are geometrically complete and electrically silent. Before quoting we ask for five things, and if a customer cannot answer them we propose values and put them in writing, because they change the price by a factor of two:
- Base alloy and temper. Cu-ETP at half-hard behaves nothing like CuBe2 at age-hardened temper. Same drawing, different spring rate, different tool wear.
- Plating stack, with thickness per layer. “Gold plated” is not a specification. 0.1 µm flash and 1.27 µm hard gold are different products at different prices.
- Mating diameter and its fit class. The barrel OD that presses into the housing is usually the tightest tolerance on the part and the one that decides retention force.
- Contact resistance budget. In milliohms, at a stated test current. This drives plating choice more than base metal does.
- Mating cycles and environment. 50 cycles indoors and 5,000 cycles with salt spray are two different plating systems.
Where the customer has no data, we quote the conservative option and say so in the offer, so nobody discovers the assumption at first article.
Base alloys: what each one is actually for
| Alloy (UNS) | Conductivity | Hardness range | Machinability | Where it earns its price |
|---|---|---|---|---|
| Cu-ETP / C11000 | 101% IACS | 45–110 HV | Excellent | General pins, terminals, busbar contacts. Cheapest conductivity per part. |
| CuBe2 / C17200 | 22–28% IACS | 180–400 HV after age | Good | Spring contacts, high cycle counts, low insertion force. The alloy for anything that must flex. |
| Phosphor bronze C51000 | 15% IACS | 90–180 HV | Very good | Socket contacts and leaf-type contacts where cost matters more than cycles. |
| C52100 (8% Sn) | 13% IACS | Higher than C51000 | Good | Higher spring force at the same section, telecom and industrial sockets. |
| Tellurium copper C14500 | 93% IACS | 90–120 HV | Best in class | Heavy-current contacts and welded assemblies; machines like brass, conducts like copper. |
| Brass C3604 | 28% IACS | 80–120 HV | Best in class | Non-critical pins, spacers, solder-cup bodies. Not for repeated mating. |
Conductivity is % IACS at 20 °C, typical mill values; hardness is the range we see across tempers. Final selection belongs on the drawing with temper called out.
Plating systems and what they cost you in tolerance
Plating is not a cosmetic step. A 5 µm deposit grows the part by 5 µm per surface, which is 0.005 mm on a diameter — the entire tolerance band of a precision contact. Pre-plate dimensions are therefore engineered backwards from the finished requirement, and the grind or turn allowance is planned before the first chip.
| System | Typical stack | Contact resistance | Mating cycles | Notes |
|---|---|---|---|---|
| Hard gold | Ni 1.27–2.5 µm + Au-Co 0.4–1.27 µm | Lowest, stable | >10,000 | Cobalt-hardened gold. The default for repeated mating and low-level signals. |
| Gold flash | Ni 1.27 µm + Au 0.1–0.2 µm | Low initially, drifts | ~50–200 | One-time mating only. Porous; copper can migrate through in humid storage. |
| Silver | Ag 3–8 µm, no underplate or Ni barrier | Lowest of all | 500–5,000 | Best for power contacts. Tarnishes — specify an anti-tarnish if appearance matters. |
| Tin | Sn 3–8 µm over Ni or Cu | Moderate | 50–200 | Cheapest. Whisker risk; requires a nickel barrier for fine pitch. |
| Nickel only | Ni 2–5 µm | Moderate-high | 200–1,000 | Wear-resistant, solderable, good for high-temperature sockets. |
| Palladium-nickel | PdNi 1–3 µm + Au flash | Low | 1,000–5,000 | Gold-price hedge for high-cycle connectors. |
Resistance figures depend on normal force and test current; the table is for material selection, not for a datasheet. We plate in-house for Ni/Sn/Ag/Au on barrel and rack, 3–7 days, with thickness verified by XRF on every lot.
Where ±0.005 mm actually matters on a turned contact
A contact usually carries five or six tolerances and only two of them drive function. Spending precision on the wrong one raises cost without improving the part.
| Feature | Typical callout | Why it matters | How we hold it |
|---|---|---|---|
| Barrel OD (press-fit into housing) | ±0.01 mm, often ±0.005 | Retention force and housing cracking | Turned on Swiss with in-process gauging; 100% optical on the OD |
| Socket bore (accepts the pin) | H8/H9 or ±0.01 mm | Insertion and withdrawal force | Bore finished with a form tool, checked with plug gauges each shift |
| Contact tip radius | R0.1–0.3 mm | Arc-free mating, no stabbing | Form tool with radius ground into the insert |
| Crimp or solder cup | ±0.05 mm | Wire insertion, solder wicking | Looser by design — do not over-specify |
| Overall length | ±0.1 mm | Stack height only | Free tolerance; specify loosely and save money |
If a drawing calls ±0.005 mm on overall length, that is a cost with no function. We flag it in DFM feedback rather than silently charging for it.
When turning beats stamping — and when it does not
The honest answer: turned contacts win below roughly 200,000 pieces a year, and stamped-and-formed contacts win above it. Turning needs no progressive die, so the tooling cost is a few hundred dollars instead of tens of thousands, and the lead time to first article is days instead of months. Above a few hundred thousand pieces the per-part economics flip hard, because a stamping line produces in one stroke what a lathe produces in one revolution.
Between those ends sits the multi-spindle lathe, which is where a lot of our connector work runs: six or eight spindles cutting simultaneously, bar-fed, with the plating done in barrels. It is the right answer for a part that is too complex to stamp economically and too high in volume for a single-spindle Swiss.
We will tell you when a part belongs in a die. Sending a 2-million-a-year contact to a turning shop is not a favour to anybody — it just moves the cost problem downstream.
What we measure, and what the report says
Every contact lot ships with a dimensional report on the ballooned drawing. On top of that, depending on the part:
- Contact resistance by four-wire (Kelvin) measurement at a stated current — dry-circuit or loaded, specified per project.
- Plating thickness by XRF, measured on the functional area, not on a witness coupon.
- Insertion and withdrawal force on a motorised test stand against a master pin or master gauge, with the first/last of the lot recorded.
- Solderability per J-STD-002 where the part is soldered, including steam ageing if the customer stores parts for months.
- Salt spray per ASTM B117 / ISO 9227 for plated parts destined outdoors or into marine environments.
Base material arrives with an EN 10204 3.1 mill certificate, and the certificate number appears on our inspection report so the chain is traceable. Where a customer needs PPAP level 3 or an AS9102 first article, we build it against the drawing package rather than reusing a template.
One limitation stated plainly: IATF 16949 is in implementation and not yet certified. Automotive programmes that require it as a gate should know that before the RFQ, not after.
Volume, lead time, and the tooling question
| Stage | Quantity | Lead time | Tooling |
|---|---|---|---|
| Prototype | 1–50 pcs | 3–7 days | None — turned from bar on a CNC lathe |
| Pilot | 50–2,000 pcs | 7–12 days | Simple form tools if the geometry needs them |
| Production | 2,000–500,000 pcs | 12–20 days | Cam or Swiss with dedicated form tools |
| High volume | 500,000+ pcs | Programmed slots | Multi-spindle; we will quote the die option too |
Plating adds 3–7 days. Mixed contact families can run as one campaign to share setup. Lead times are working days from drawing approval, not from RFQ.
Related guides and capabilities
Custom CNC pins · Brass turned parts · Aluminium turned parts · Swiss screw machining · Surface treatment & plating · Tolerance capability
Request a quote
Send drawing (STEP / PDF / DXF) with material, tolerance and annual volume to mc@chxmetal.com. DFM feedback and a price within 24 hours, NDA on request.
Get a CNC quote · Contact CHX Metal · Supplier profile & certificates
Frequently asked questions
What is the smallest contact you can turn?
Ø0.8 mm on the Swiss cell, with optical measurement at recorded temperature. Below that, handling and burr control dominate the process and the economics stop making sense for most programmes.
Can you hold ±0.005 mm on a plated diameter?
Yes, by pre-sizing. The plating deposit is added to a deliberately undersized turned dimension. We plan the allowance from the specified thickness, so a 5 µm gold layer lands the part inside the band rather than on the upper limit.
Do you supply the mating housing too?
Often, yes — the same plant machines the insulator housing, the retention clip and the contact, which removes the tolerance stack argument between two suppliers. Where the housing is moulded, we machine the contact to the housing supplier's measured cavity.
How do you control insertion force without a spring?
With the bore geometry and the contact's own slotted or leaf features. Force is set by the interference between the socket bore and the pin, and by the alloy's spring rate. We cut test parts, measure force on a motorised stand, and adjust the bore before releasing the production program.
Can you mark or laser-etch parts?
Yes — laser marking on the barrel or on a flat, with a Data Matrix if the customer needs unit traceability. Marking is quoted as a separate operation because it changes cycle time.
What is the minimum order?
One piece for a prototype. There is no MOQ gate on the turning side, though plating has a practical barrel minimum that we will state in the quote.
Do you work to US or European drawing standards?
Both. ASME Y14.5 and ISO 1101 GD&T are read in-house, inch and metric drawings both run, and the inspection report is issued in whichever unit system the drawing uses. Mixed-standard drawings are flagged in DFM feedback rather than guessed at.
Send your drawing, get a price in 24 hours
Name, email and what you need. Attach a drawing if you have one — STEP, PDF, DXF or a photo of the print. We reply with unit price, MOQ and lead time, usually within one working day.
Prefer email? Send drawings to mc@chxmetal.com.