Swiss Turning Tolerance Guide

OD Turning

Standard Swiss production holds ±0.0005" on outside diameters as a matter of course. With careful setup, ±0.0002" is achievable and repeatable across long production runs. Guide bushing machines inherently produce better OD concentricity than conventional lathes because the work is supported at the cut point. For diameters under 0.250", ±0.0001" is possible with skim cuts and controlled thermal conditions, though this adds cycle time.

Boring & ID Features

Internal features are more challenging than OD work on Swiss. Standard boring holds ±0.001" comfortably. With precision boring bars and carbide tooling, ±0.0005" is production-realistic. Cross-drilled holes and off-center bores require careful fixturing in the sub-spindle. Deep bores (depth > 3x diameter) may require peck cycles that add cycle time.

Threading

Single-point threading on Swiss holds class 2A/2B fit consistently. Class 3A fit is achievable with sharp threading inserts and proper synchronization. Thread whirling — available on most modern Swiss machines — produces medical-grade thread profiles (bone screw threads, buttress threads) with excellent surface finish and no burrs.

Length & Cutoff

Part length tolerance from cutoff is typically ±0.002" to ±0.005" depending on the cutoff tool width and bar stock quality. If tighter length control is needed, a facing operation in the sub-spindle brings this to ±0.001" or better. Bar stock diameter variation directly affects length consistency.

Cross-Work (Milling, Drilling)

Cross-holes: ±0.002" position, ±0.001" diameter. Milled flats: ±0.001" depth. Hexagonal features: ±0.002" across flats. Cross-work is limited by the power and rigidity of the tool gangs — these are small tools on small parts. Deep cross-features may require multiple passes.

Surface Finish

Swiss machines routinely produce Ra 16–32 μin on OD surfaces. With sharp carbide inserts and proper feeds, Ra 8–16 μin is achievable. Burnishing attachments can push surface finish below Ra 4 μin on ductile materials. Thread whirling produces Ra 16 μin or better on thread flanks.