Swiss screw machining is an efficient way of producing cylindrical parts from bar, especially those with large length-to-diameter aspect ratios. Swiss CNC machine tools are precise, and a fast and repeatable means of turning complex parts.

But, this high productivity magnifies the need to find improvements. That’s because Swiss machines typically handle long production runs, where small time savings per piece become large gains. Accordingly, this blog offers some advice for anyone exploring the process as a possible production method, or designing parts to be made this way.

What is Swiss Screw Machining?

Swiss screw machining is a form of turning, and a Swiss screw machine is a highly evolved form of CNC lathe. The main element of the machine distinguishing it from conventional lathes is the guide bushing. This does the work of the chuck in a regular lathe by holding and rotating the workpiece.

Unlike a chuck, a guide bushing can feed the material axially out into the work envelope. This eliminates the need for cutting tools to traverse along the axis of the chuck/bushing and reduces workpiece deflection when cutting.

Swiss machines are almost always bar-fed, with up to eight spindles arranged in a drum. This can index through multiple stations, taking the bar/workpiece to different tools at each one. In addition, powered tools can perform tasks like milling and drilling cross holes. Furthermore, most Swiss machines also have a second spindle used to finish the back of the part once it’s been parted off from the bar.

9 Tips for Optimizing Efficiency

1. Use quality bar stock: Clearance between bushing and bar stock should be minimized, which is achieved by using ground bar. For best results, consider using “Screw Machine Quality” (SCM(TM)) where straightness and diameter consistency exceed the ASTM standard.
2. Maintain guide bushings: Wear affects their ability to hold the bar concentric and feed it forward.
3. Use the right guide bushings: Use fixed rather than synchronous rotary bushings when trying to maintain tolerances tighter than +/-0.0005”.
4. Utilize spindles effectively: Ideally, metal removal takes place at each spindle for the same length of time. If one spindle works longer than the others the workload is unevenly distributed and the production rate will be lower than it could be.
5. Prevent chip build-up: Swiss machining uses oil rather than water-based cutting fluids, which generates more heat. This compounds the problem of long, stringy chips building up around the cutting tool, with friction raising temperatures further. This kind of chip build-up forces frequent stops so an operator can clear the mess. Consequently, pay close attention to effective chip breaking, especially with ductile and tough materials like 4140 stainless, 7075 series aluminum, and Ti-6Al-4V titanium.
6. Use modular tooling: The large numbers of tools and axes make Swiss CNC machines complicated to changeover. Modular tooling, where blocks can be swapped-out quickly, saves time, allowing production to restart sooner.
7. Use a tool presetter: When chasing tight tolerances it’s extremely important to get the tool offsets right. A high-end tool presetter generates very precise offset values, and can even transfer them directly to the machine tool, saving time and avoiding transcription errors.
8. Minimize bar size changeovers: Changing bar sizes is a long and complicated job. Sequence orders by bar stock diameter to reduce the frequency with which this is done, and increase productive capacity.
9. Invest in programming capabilities: Swiss CNC machines are complicated to program. Invest in the latest Computer Aided Manufacturing (CAM) software and ensure engineers responsible for writing programs are trained to get the best from it.

Find a Shop That Understands Swiss Screw Machining

Small efficiency improvements on Swiss-style CNC machines can lead to large quality, capacity, and cost benefits. If you’re working with or looking for, a CNC machine shop to produce smaller, complex turned parts, make sure they understand how to maximize efficiency.

Impro carries out Swiss screw machining work for clients in industries like automotive, medical devices, and industrial equipment. Contact us to discuss your next project or part requirements.