Loothprint Looth Lite

Fret Sander V2

A 3D-printed sanding tool for polishing out scratches after re-crowning frets — with swappable, parametric fret-radius caul inserts and a spool-fed sandpaper feed that runs lower grits with less friction.

Dave Slimmer OldSchoolGuitar The Looth Group

July 19, 2026 · 2 min read

Tools, Jigs and Fixtures Repair Tool 3d printing dave slimmer fret dressing fret sander fretwork fusion 360 guitar repair oldschoolguitar parametric setup tool

My favorite way to remove scratches after re-crowning frets is to use 400, 600, and 1000 grit sandpaper, followed by 0000 steel wool and Dremel-tool buffing. My old fret sander had a couple of disadvantages: it didn't fit my hand very well, and its fret radius was good for medium-size frets but not for smaller or larger ones.

The idea for this tool comes from a YouTube channel called The Next Project — I expanded and adapted ideas from their tool “The Grip” to make the FretSander (links below). Many of the differences between “The Grip” and the FretSander address reducing the friction of the sandpaper travel, so it can use lower grits.

Labeled parts of the FretSander: the handle, the sandpaper feed spool and take-up spool, and the fret-caul inserts in their caddy.

One of the FretSander's features is the swappable fret-caul insert. I've included a parametric design file so you can create custom sizes. To use it, open FretCaulInsert.f3d in Fusion 360, select Modify → Change Parameters, and change the fretdiameter parameter. Remember to add the thickness of your sandpaper to the diameter of your frets — for example, my 400 grit paper is about .009″ and my 600 grit is about .008″ thick. The toleranceslip parameter lets you adjust how tightly the caul insert fits in the FretSander handle.

I wanted the caul-radius labels to update automatically, so I used a parametric-text Fusion add-on (linked below). Fusion 360 now supports parametric text natively, so the add-on is no longer necessary if you update the FretCaulInsert file. I've also included a set of ready-to-print .stl files covering a range of fret sizes.

For the FretSander handle I used a 0.20 mm layer height with the variable-layer-height option, to get a smoother surface finish on the contours. Print the spools and fret-caul inserts standing vertical for best results.

When holding the FretSander I use my thumb and index finger to gently squeeze and pull up on the sandpaper. This keeps the paper from sliding around while sanding a fret. When it's time to advance the sandpaper, I release finger pressure. The FeedSpool is designed to turn counter-clockwise to minimize sandpaper friction against the handle.

The paper cutter seen in the video was purchased from Harbor Freight just for cutting sandpaper strips — I've used it for several years and it still makes clean cuts.

Any resemblance between the FretSander and the Jawa sandcrawler is purely coincidental.