What tips can improve the surface finish of CNC machined precision parts

Finishing cutting is the last step before a precision part reaches inspection, and after all the time and effort to manufacture a precision part, it is critical to produce a high-quality surface finish. Incorporating a few key practices can help prevent the need to scrap parts in the final stages and ensure your finish stays on track.

1. Feed and Speed

This may seem like an obvious point, but using the correct feeds and speeds is critical to getting a high-quality finish on precision parts. Increasing the tool speed reduces the combined edge (BUE), while reducing the feed reduces flank wear. Both reduce the likelihood of tool failure and extend tool life. One caveat though: so far, don't dial back the depth of cut so that the tool rubs against the surface instead of cutting it. This will result in a smearing effect.

Second, the chip breaker

While it may seem satisfying to see a long spiral of chips come off the tip of the tool, those long chips may mean that the cutting pressure is too high. This results in accelerated tool wear and a pile of metal strips that can damage the surface of precision parts. Adding a chipbreaker improves chip removal and control. Factors such as part ductility, tool shape, milling setup, and coolant use can all influence the choice of chipbreaker, but once the correct chipbreaker is implemented, it is easy to clean the chips before they touch the finished surface.

Three, positive front angle

In addition to lowering BUE and using chip breakers to break up chips, increasing the rake angle helps produce more manageable chips, which increases cutting efficiency and reduces tool wear, resulting in a more precise surface finish on machined precision parts.

Fourth, maintain rigidity

It is very important that the knife holder remains rigid throughout the cutting process. Any moving pockets in the setup can cause chattering and cause a scalloped surface. Additionally, best practices such as using the shortest tool reach and appropriate feed rates and minimizing tool deflection can also minimize chatter.

5. Use finishing tools

Roughing tools and finishing tools are very different beasts. Although using the same tool for both may seem like a cost saving measure, it may result in a larger amount of scrap after the completion stage. Additionally, the desired surface finish may require different tool and insert geometries than roughing cuts. Consider using a different nose radius, finer pitch or wiper insert for finishing cuts.