Cutting nut slots is one of the most delicate jobs in guitar and bass setup. It’s also one of the easiest to get wrong.
A common mistake is cutting nut slots deeper and deeper in an attempt to lower the action. While this can appear to work at first, it often leads to slots that are too wide, strings that can move side-to-side, and tuning instability.
- What over-cut nut slots look like
- Why this happens
- The correct way to lower nut action without damaging the nut
When nut slots are cut too deep, the string becomes fully buried in the slot. At this point, the file begins to contact the upper edges of the nut rather than just the base of the slot.
This causes two problems:
- The slot becomes wider at the top than it needs to be
- The string is no longer properly supported
If your slots look wide and the strings are no longer visible sitting above the nut, the slots have already gone too deep.
If the action at the nut is too high, the correct fix is not to keep cutting the slots deeper.
Instead:
- Remove the nut carefully
- Place it flat on sandpaper on a truly flat surface
- Remove small amounts of material from the base of the nut
- Refit and check the height
This approach keeps the slots narrow and stable while achieving the desired action height.
Once the nut height has been corrected by sanding the base, the slots can be cut to their final depth.
- Use the correct file size for each string
- File only the lower portion of the slot
- Maintain a clean break angle toward the tuners
- Remove material gradually and check frequently
The goal is correct support and clean break points — not burying the string.
Once refitted, a correctly set nut will show:
- Strings sitting slightly proud of the nut
- Only the lower portion of the string supported
- Clean break points at the fingerboard edge
Why This Matters
By adjusting nut height at the base rather than chasing action by deepening the slots, you avoid:
- Widened slots
- Loose strings
- Unnecessary nut replacement
Final Thoughts
If a nut file feels “too wide”, it’s almost always a sign that the slot has already gone too deep.
Set the nut height first. Cut slots carefully and minimally. And when action needs adjusting, sand the base — not the slots.
If you’re unsure at any stage, stop and reassess. It’s far easier to remove a little material later than to fix an over-cut nut.
