Fretboard radius sanding block generator

Because the two parts are not asking the same thing. A bobbin has holes a magnet has to go through, and a facetted hole no longer measures its diameter across the flats: a 5.2 mm hole cut in twelve sides measures 5.02, and the pole does not fit. A radius block has nothing to fit into. Its surface gets sanded, the slicer turns every curve into polygons anyway, and the STL is the file the 3D printing world actually asks for. So you get both here.

By less than you can measure. Paper is about 0.3 mm thick, so the sanding surface sits 0.3 mm inside the block. On a 241 mm radius that moves the hollow of a 57.2 mm board by 0.004 mm. That is why there is no field for it: a printer holds a tenth of a millimetre at best.

Vintage Fender is 7.25 in, modern Fender 9.5, PRS 10, Gibson 12, and a lot of newer necks run 12 to 16 or flatter still. Classical guitars, most ukuleles, mandolins and banjos are flat and need no block at all. If you are working from a neck that already exists, measure it with a radius gauge rather than trusting the catalogue.

No. A compound board is a cone: the radius grows along the neck, so no single cylinder fits it. Print the radius at the nut and the radius at the last fret, and blend between them. The fret calculator prints the radius fret by fret, which tells you where each block belongs.

You cannot see it: a 12 in hollow is two and a half millimetres deep on 70 mm of width. The radius is in the file name and in the header of the STL file, and the honest answer is to write it on the part with a marker as soon as it comes off the plate.