A leading Scotland-based supplier of high technology sub-assemblies for use in the oil industry has made significant savings by utilising helical interpolation thread milling with single point tooling. 

The tooling was supplied by Horn Cutting Tools Ltd via Scottish distributor, Peter Campbell Sales Ltd.  On one job alone, the switch from multi-flute inserts to a Horn Supermini® Type 105-derived special tool to produce 0.25 inch UN threads saves thousands of pounds per year due to longer tool life and reduced insert cost. 

In addition, superior thread quality as defined by improved parallelism and cleaner thread profiles has virtually eliminated rework requirements.

This application was one of a wider program of conversion to single point thread milling.  The end user company operates in a sector where quality is critical, machining substantial components from materials like 420 grade stainless, 4140 stainless and Inconel 718 using a variety of high quality CNC machine tools.

These alloys represent a machining challenge in any circumstance.  However the problem is often compounded by difficulties relating to accessing the location of the designated feature.

In the case of the 0.25 inch thread instanced above, the feature is machined in the front face of a shoulder situated about 200 mm from the front face of the component.  This demands use of a lengthy extension bar to present the threading tool to the bore, which is itself counterbored at the entrance.

The company’s production engineer commented. “With the multi-flute tool that we used previously there was a cumulative rigidity problem because of the way that the tool interfaced with the holder.  This led to quite rapid wear of the tool which compromised the quality of the thread.”

The solution introduced by Horn utilises a purpose-built long length tool holder.  This is produced to the maximum cross section that can still clear the spigot and access the bore. 

The bar is tapered at the business end to a short tool holder section.  The Type 105 thread milling insert clamps directly to the holder using a single central screw.  Torque is transmitted by precision machined matching interfaces on the tool holder nose and insert back designed so that the assembly acts as a solid entity.