Summary

Professional nut files are highly specialized tools and often cost hundreds of euros for a complete set. This simple DIY alternative offers a low-cost, practical solution for making and improving guitar nut slots.

A standard feeler gauge (100 × 10 mm with a ca. 5 mm hole), costing only a few euros, can be converted into a functional nut file by cutting fine teeth into the gauge blade with a file. Used on its own, a feeler gauge is too flexible and uncomfortable to hold, which can cause wobbling during filing. This wobble makes it difficult to control the cut and can result in nut slots becoming too wide, especially when working with thinner string gauges. To solve this, the modified blade is mounted into a 3D-printed plastic holder, which stabilizes the gauge, improves ergonomics, and ensures accurate, straight cuts with proper slot width.

While this tool does not cut as fast as professional diamond-coated nut files, this can be an advantage:
the less aggressive cutting action greatly reduces the risk of filing the nut slot too deep too quickly, allowing for better control and precision—especially for beginners.

With a single feeler gauge set, you can create a full range of nut files for different string gauges, making this an affordable, versatile, and effective solution for hobbyists and DIY luthiers.