Tool breakage is one of the major challenges in Swiss-type machining. A tool itself is already costly, and when it breaks, machine downtime, tool changes, re-setting tool offsets, and first-article verification cost several times more in lost time than the tool itself.

More troublesome still, if breakage of a preceding tool is not detected in time, subsequent tools may break one after another, and a single downtime may scrap several tools.

In fact, the causes of tool breakage are not complex. Troubleshooting should follow a sequence: cutting oil → chipbreaker → parameters → clamping, checking each one by one.

① First check whether cutting oil flushing is adequate

Inadequate cutting oil flushing is one of the common causes of tool breakage.

Swiss-type tools are small and spindle speeds are high. Cutting oil must precisely cover the tool tip and chip evacuation area to provide cooling and assist chip removal.

Recommendations: increase the cutting oil coverage area, check whether the oil pipe nozzle is aimed at the tool tip, and verify whether oil pressure is sufficient.

For deep-hole or internal groove machining, high-pressure through-spindle coolant can be used. Cutting fluid passes directly through the spindle and tool center to the tool tip, achieving chip evacuation and cooling in one step. Tool life can be increased by more than 2 times.

If conditions permit, check the cutting oil level and whether the filter screen is clogged. Periodically stop the machine to clean chips according to the material being machined—this is far more cost-effective than waiting until a tool breaks.

② Check whether the chipbreaker matches the material and machining conditions

If the chipbreaker is selected incorrectly, chips will not break and will wrap around the tool tip, greatly increasing the probability of sudden overload breakage.

When selecting a chipbreaker, focus on three things: workpiece material, feed rate range, and tool tip strength requirements.

According to the feed rate range, choose a chipbreaker with a moderate opening to ensure chips break rather than pack near the tool tip.

For stainless steel, choose a sharper chipbreaker and use a slightly higher feed rate so chips break at the root.

Simply put: choose robust geometries for roughing and sharp geometries for finishing; do not use one tool for all operations.

③ Parameters and clamping

Parameter overload is a direct cause of carbide tool breakage. Excessive depth of cut and feed cause the cutting load to exceed limits.

When machining small-diameter parts on a Swiss-type lathe, stepped depth of cut is much safer than cutting to final depth in one pass.

In terms of clamping, worn collet bore or chips and oil contamination on the taper surface can reduce clamping force, causing tool slip and uneven force, which directly leads to tool breakage.

Before clamping, thoroughly clean the spindle taper bore and toolholder contact surface, and keep tool overhang as short as possible. This is much less troublesome than re-setting tool offsets after a breakage.

When it comes to tool breakage, spending a few extra minutes on the shop floor to troubleshoot in sequence is worth far more than spending half an hour changing tools and re-setting offsets after breakage.