Guides / Industries

Swiss Machining for Connector Pins and Electrical Contacts

September 21, 2026

Connector pins are one of the highest volume categories on Swiss-type lathes. They are small, round, turned to several diameters, often plated and bought in hundreds of thousands. Almost every trait that makes Swiss machining economical is present at once.

The sourcing challenge is rarely capability. It is specifying the part so that quotes from different shops describe the same thing, because on a part costing cents, small scope differences move the price by a large percentage.

Why these parts suit Swiss machining

A typical contact pin has a mating diameter, a shoulder, a retention feature such as a barb or a groove, a termination end and sometimes a cross hole or a flat. All of it is small, all of it is round and all of it has to be concentric.

A Swiss-type lathe cuts the whole front end in one chucking, so the mating diameter and the retention groove sit on the same axis by construction. The sub spindle finishes the termination end. The part comes off complete, at a cycle measured in seconds, running unattended from a bar feeder.

Once the job is set up, cycle time is the price. This is why volume matters so much on connector work and why the conversation with a shop should start with your yearly quantity rather than your first order. The cost guide shows how the numbers move.

For connectors that carry a radio frequency signal rather than simple power or logic current, dimensional control on the mating interface and shielding continuity matter as much as the diameters themselves, covered in the RF connector guide.

Material

Connector materials are chosen for conductivity, spring behavior and cost, then checked for machinability.

Brass C360 is the default where conductivity requirements are moderate. It is the fastest material on the machine, breaks chips cleanly and gives long tool life. Where the application allows brass, it is almost always the lowest cost route.

Lead free brass appears where RoHS, drinking water or other regulations exclude leaded grades. It machines noticeably less easily than C360, so do not assume the same price or the same cycle. Say explicitly which grade applies rather than writing brass.

Phosphor bronze and beryllium copper are used where the contact needs spring properties. Beryllium copper is heat treatable and holds contact force well, and it costs more in both bar and machining.

Copper alloys with machining additives sit between pure copper and brass. Pure copper is difficult on a Swiss machine because it is soft and gummy and smears rather than breaking chips.

Stainless appears for corrosion resistance in harsh environments, usually with a plated contact surface.

If conductivity is the driver, ask your electrical engineer for the minimum acceptable conductivity rather than a material name. It sometimes opens a cheaper option. The materials guide compares the machining behavior of each family.

Plating is where the money and the errors are

Most connector pins are plated. Gold on the mating surface for low contact resistance, nickel as an underplate and diffusion barrier, tin or tin alloy on the termination end.

Four things must be on the drawing:

1. Metal, thickness and tolerance, for each plated layer
2. Where each plating applies, since selective gold plating on the mating area only is far cheaper than plating the whole pin
3. Whether dimensions apply before or after plating, stated explicitly
4. Masking boundaries, if plating is selective, with a tolerance on where the boundary sits

Gold thickness is a direct cost driver and it is frequently overspecified. A contact rated for a small number of mating cycles in a benign environment does not need the same gold as a high cycle industrial connector. Ask whether the thickness on your drawing came from analysis or from a previous part.

Also decide whether you need plating thickness measurement and a certificate with each lot. On electrical parts this is usually yes, and it belongs in the quoted scope rather than added later. The secondary operations guide covers how plating fits the sequence.

Tolerances on very small parts

Contact pins carry some of the tightest tolerances in ordinary production, and the features that matter are usually few.

What typically matters:

• Mating diameter, controlling contact force and insertion force
• Concentricity between the mating diameter and the body, so the pin enters its housing cleanly
• Retention feature dimensions, controlling whether the pin stays seated
• Overall length and shoulder position, controlling seating depth
• Surface finish on the mating area, since finish affects contact resistance and plating adhesion

What usually does not matter: everything else. On a part this small it is tempting to tolerance the whole drawing tightly because the numbers look small anyway. Resist it. Each tight band adds a finishing pass and in-process gauging, repeated across every part in a run of hundreds of thousands. The tolerances guide covers how to distribute them.

One trap specific to small pins: measurement force. A thin section deflects under a micrometer, and two people measuring the same pin can disagree by a meaningful fraction of the tolerance. For anything critical, state the measurement method.

Housing fit and the features that control it

A pin is never evaluated on its own. It goes into a housing, and most field failures trace back to how the two interact rather than to a dimension being out of band.

The features that matter:

Retention geometry. A barb, a knurl or a groove holds the pin in the housing. Too small and the pin backs out under mating force. Too large and it deforms the housing or cannot be inserted. This dimension usually deserves a tighter band than anything else on the part.

Lead-in geometry. The chamfer or radius at the insertion end controls whether the pin enters cleanly or shaves the housing bore. A sharp edge here produces plastic debris inside the connector, which is a contamination problem as well as a retention one.

Shoulder position. Controls how deep the pin seats, which controls mating alignment.

Concentricity between the mating diameter and the retention feature. If these are not on one axis, the pin sits cocked in the housing and contact alignment suffers.

The useful instruction is to tell the shop what the part mates with. A drawing showing a pin alone leaves the shop guessing which features are functional. A note saying which diameter enters the housing and which feature retains it lets a good shop flag a problem before cutting metal.

Qualification testing reaches back to the pin

Connector programs usually run a qualification sequence: mating cycles, thermal cycling, vibration, humidity and contact resistance measured through it.

Several machining characteristics show up in those results. Surface finish on the mating area affects contact resistance and plating adhesion. Burrs at the retention feature affect insertion force and housing damage. Plating thickness affects durability over mating cycles. Base material affects spring behavior where the contact flexes.

If your part is entering qualification, say so. A shop that knows the parts are going into a test sequence will treat process consistency differently from one making an industrial fitting, and it will keep records you may need if a test result has to be investigated.

High volume economics

Connector programs run in volumes where small changes compound.

Seconds matter. At 500,000 pieces a year, one second of cycle time is roughly 140 machine hours. A feature that needs an extra tool pass is worth questioning.

Bar utilization matters. Cut off width and bar remnant are a larger share of a small part than of a large one. Ask how many parts the shop gets per bar.

Tool life matters. Insert changes are machine downtime. A material or a tolerance that halves tool life has a real cost at these quantities.

Packaging matters. At high volume, packaging labor per part can rival machining. Bulk, tape and reel, tray or bagged in counted quantities are very different costs. Specify it.

Scrap rate matters. On a cheap part the scrap cost is mostly the machine time already spent. Agree how yield is handled and whether the shop runs overage to cover plating losses.

Writing a connector pin RFQ

Include:

1. STEP file and drawing, with critical characteristics identified
2. Material grade, specifically, including whether lead free is required
3. Plating, with metal, thickness, location, masking and before or after dimensions
4. Contact resistance or conductivity requirement, if there is one
5. Yearly volume and expected order pattern
6. Packaging format and quantity per container
7. Documentation required, including plating certificates
8. Any industry or customer specification the part must meet

That third item resolves more quote differences than anything else on the list.

Getting connector parts quoted

Send the package through the RFQ form with the yearly volume stated. We match the part with up to three shops that run Swiss-type lathes and reply within 24 business hours.

On parts this small, ask each shop for price breaks at several quantities. The curve tells you where your order size should sit, and it is more useful than a single number. On parts costing cents, the difference between the right quantity and a convenient one is often larger than any negotiation you could win on the rate. The minimum order quantity guide explains how to read it.

See also: contact alloys, plating stacks and contact sizes.

Frequently asked questions

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