Guides / Industries

Swiss Machining for Hydraulic and Pneumatic Fitting Components

September 21, 2026

Hydraulic and pneumatic components sit naturally on Swiss-type lathes when they are small: fittings, adapters, cartridge bodies, valve spools, orifices, nozzles and check valve parts. They are round, they carry several turned features and they repeat in volume.

What separates them from ordinary turned parts is that they have to seal, and they have to not shed debris into a system. Both requirements land on the drawing in ways that are easy to specify badly.

The parts

Common Swiss work in fluid power:

Fittings and adapters. Port thread on one end, tube or hose connection on the other, hex or flats in the middle, a through bore.

Valve spools. Several precise diameters with grooves between them, tight concentricity, controlled edge condition where the spool meets the port.

Cartridge and cavity components. Bodies and sleeves with O-ring grooves and cross holes.

Orifices and nozzles. Small precise bores controlling flow, often with a finish requirement in the bore.

Check valve parts. Seats, poppets and guides, where the sealing geometry is the function.

Above roughly 32 mm the part moves outside typical Swiss bar capacity. The pillar guide covers where that limit sits and why.

Sealing surfaces

A sealing surface is not an ordinary turned diameter, and the drawing has to say so.

Metal to metal seats need a controlled surface finish, a controlled angle and freedom from the tool marks that ordinary turning leaves. Specify the finish with a measured parameter, not a word.

O-ring sealing surfaces depend more on the groove than on the bore or the spigot, but the surface the O-ring slides across during assembly still matters. A rough surface or a sharp lead-in edge cuts the seal during installation.

Face seals need flatness as well as finish, and flatness on a small turned face is a different measurement from diameter.

State which surfaces are sealing surfaces explicitly. A shop reading a drawing with uniform general finish has no way to know which face is doing the work. The surface finish guide covers how finish is measured and what is typical off a Swiss machine.

O-ring grooves

Groove geometry is where fluid power drawings most often go wrong, usually by inheriting dimensions from a previous part rather than from the seal supplier’s data.

What belongs on the drawing:

• Groove diameter with tolerance
• Groove width with tolerance
• Corner radii at the groove bottom
• Surface finish in the groove, which affects both sealing and seal life
• Edge condition at the groove shoulders

The width matters for manufacturing as much as for sealing. A groove width matching a standard grooving insert runs on stock tooling. A width off by a fraction of a millimeter forces a ground tool, which adds setup cost and a lead time risk. Before finalizing, check whether a standard insert width falls inside your seal supplier’s acceptable range. It frequently does, and the design guide covers the same principle across other features.

Burrs and the fluid path

A burr that breaks loose inside a hydraulic system can damage components far more expensive than the fitting it came from. This is why fluid power drawings carry deburring requirements that look excessive next to general machining.

The problem is that “free of burrs” is not inspectable as written. Make it specific:

1. Name the locations. Cross hole intersections, thread starts and ends, groove shoulders, bore entries. These are where burrs actually survive.
2. State the condition required. A defined edge break with a dimension is easier to verify than an absolute.
3. State the verification method. Visual at a stated magnification, borescope for internal intersections, or a flow and cleanliness test.
4. State a cleanliness requirement if you have one. Particle count standards exist for fluid power components, and if your system needs one, say which.

Internal cross hole intersections are the hard case, because a tool cannot always reach them. Shops address this with thermal or electrochemical deburring, with specific drilling sequences or with flow through cleaning. Each has a cost, and the method matters less than the verified result. The secondary operations guide covers how these steps fit the job.

Threads

Port threads carry pressure, and the fit class matters more than on general hardware.

Specify:

• The thread standard and size, exactly
• The fit class or tolerance class
• Thread depth and any relief
• Whether thread sealant, a coating or a preapplied sealing element is required
• How threads are verified, since go and no go gauges are the practical production answer

Tapered port threads have their own gauging practice and their own tolerance behavior. If your port is tapered, confirm the shop gauges to the correct standard rather than assuming.

Cross holes and drilling strategy

Most fluid power components have at least one cross hole intersecting a through bore, and that intersection is where the difficult requirements live.

Three things happen there. The drill breaks into an existing bore and produces a burr on the far side. The intersection creates a stress concentration, which matters on pressure cycling parts. And the geometry is hard to reach, inspect and clean.

What affects cost and quality:

Drill entry and exit conditions. A hole that breaks through at a shallow angle produces a larger, more tenacious burr than one breaking through square. If the angle is a design choice rather than a requirement, squaring it up helps.

Drilling sequence. Some shops drill the cross hole before the through bore so the burr is removed by the later operation. Whether this is possible depends on the geometry, and it is the kind of process choice worth leaving to the shop rather than dictating.

Hole diameter relative to depth. A deep small hole needs pecking or a special cycle and runs slowly. The design guide covers the general ratio limits.

Multiple holes on different planes. Each plane needs its own indexing operation. Grouping holes on as few planes as the design allows shortens the cycle.

Cavity conformance on cartridge parts

Cartridge valves and their cavities are defined by industry standard cavity forms, and conformance is not something you can judge by eye.

If your part goes into a standard cavity, name the standard and the cavity designation on the drawing rather than reproducing the dimensions yourself. Transcription errors here are common and expensive, because a part that misses the cavity form by a small amount seals unpredictably rather than failing outright.

Ask how the shop verifies cavity conformance. A dedicated gauge is the usual answer on production parts, and obtaining one can take longer than making the first lot. Settle it before the first order rather than after, the same way you would for a non standard thread gauge.

Materials

Fluid power parts are usually one of four families:

Brass for low to moderate pressure fittings, fast to machine and easy to seal against, covered in the brass guide. Carbon and alloy steel for higher pressure, usually plated or coated for corrosion resistance. Stainless where the fluid or the environment requires it, most often 303 for general work and 316L where corrosion resistance drives the choice. Aluminum where weight matters and pressure allows.

Pressure rating is a design question rather than a machining one, but it reaches the shop through material, wall thickness and finish requirements. Tell the shop the working pressure and the fluid, because both affect what the part needs. The materials guide compares how each family behaves on the machine.

Testing

Some fluid power components ship with a test.

Decide and state whether you need:

• Proof pressure testing, at what pressure and for how long
• Leak testing, by what method and to what acceptance
• Flow testing, where an orifice or a nozzle controls flow
• Cleanliness verification
• A certificate recording the result with each lot

Testing is per part rather than per lot in most cases, so it can be a significant cost on small inexpensive components. Ask for it if you need it and leave it out if you do not.

What to send with a fluid power RFQ

1. STEP file and drawing, with sealing surfaces identified
2. O-ring groove dimensions from your seal supplier’s data
3. Thread standard, size and fit class
4. Deburring requirement with locations and verification method
5. Working pressure and fluid
6. Material and any coating or plating
7. Testing requirements
8. First order quantity and yearly volume

Getting fluid power parts quoted

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

If the part is above roughly 32 mm in diameter, expect to hear that a conventional lathe fits better. That is usually the cheaper answer, and we would rather tell you than pass the request along.

If the part seals against something, say what it seals against and at what pressure. That single line in the notes changes how a shop reads every finish and groove callout on the drawing, and it is the detail most often missing from a fluid power RFQ.

See also: port standards, sealing faces and cleanliness for fittings.

Frequently asked questions

Keep reading

• Valve Spools on Swiss Lathes: Fits, Roundness and Finish
• Watch and Clock Parts on Swiss Lathes: Pinions, Winding Stems and Screws