Neat threads
A Scotland-based supplier of high technology sub-assemblies for use in the oil industry has made significant savings by using helical interpolation thread milling with single point tooling. The tooling was supplied by Horn Cutting Tools via Scottish distributor, Peter Campbell Sales.
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 programme 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 200mm 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 comments: '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 uses 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.
This format offers significant advantages over the previously used system. The tool assembly is more rigid whilst the cutting forces developed by the single point cutter are lower than those attributable to a multi-flute cutter, reducing the risk of vibration.
The production engineer continues: 'The Horn set-up provides a more consistent high quality thread, which eliminates the need for rework. Moreover, tooling costs are significantly lower.' This last is attributable to longer tool life and much lower unit cost for the Horn insert. He adds: 'There is a marginal time penalty but this is offset by the improved as-machined quality, whilst the fact that we are not producing thousands of threads means cycle time is not a major issue.'
As well as single point thread milling using Supermini Type 105 the company has also adopted Horn Type 300-series thread milling for diameters up to around one inch. Overall the switch to single point thread milling has reduced tooling costs by around 66%. 'We’re very satisfied with the outcome; the conversion to Horn single point threading has provided all-round benefits for our production process.'
