Precision luthier tools. Made in Virginia, USA. Lifetime Warranty.

  • Set of five 3.5 inch wide radius sanding blocks for extended-range guitars and basses
  • Radius sanding block side view showing curved sanding face
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Luthier Tools > Radius Sanding Block Set, 5-Block (3.5″ Wide)

5 Radius Sanding Block Set (3.5″ Wide)

5 Radius Sanding Block Set (3.5″ Wide)

$70.00
$70.00
Sale Sold out
$70.00
Lifetime Warranty  ·  Made in Virginia, USA  ·  Ships in 3-4 business days

3.5″ wide. 5 blocks. Your choice of radii.

A set of five radius sanding blocks for setting fretboard profile during a new build, restoring the radius during a refret, or leveling frets to the board's existing curve. 3.5″ width fits extended-range guitars (7-9 string) and basses (5-7 string).

Radius & Length

Lengths

  • 4″ for spot work
  • 8″ and 10″ for general fretboard sanding

Radii

  • Imperial: 7.25″–30″
  • Metric: 390mm–430mm
  • Flat
  • Custom: email us for a radius we don't list, no extra charge

Sandpaper

3.5″ wide adhesive-backed sandpaper isn't a standard size. Two ways to handle it:

  • Trim a wider PSA roll. 4-1/2″ rolls cut down to 3.5″ with scissors or a straightedge and utility knife. Klingspor's 4″ roll category covers most grits.
  • Use standard sheet sandpaper. Cut to size and attach with double-sided tape or a light coat of spray adhesive.

Material

3D-printed in PLA. Reasoning is in Why We Use PLA. Covered by our lifetime warranty if any block ever fails.

Working on a full build?

The Fretboard Radius Jig establishes the radius with a router in under ten minutes. The blocks then smooth the board after, a couple of minutes per grit. Many builders run both: jig for stock removal, blocks for finishing.

Want different quantities or a single block?

Buy single blocks at Radius Sanding Block (3.5″ Wide).

Specs

Width 3.5″
Length
  • 4″
  • 8″
  • 10″
Quantity 5 blocks
Radius
  • Imperial: 7.25″–30″
  • Metric: 390mm–430mm
  • Flat
  • Custom
Material PLA
View full details

How to Use

At a glance

  • Apply 3.5" wide sandpaper to the curved face. Trim flush.
  • Sand lengthwise along the fretboard with even pressure. Do not twist.
  • Step up through grits as the surface evens out.

Step-by-step

  1. Apply sandpaper. Press sandpaper firmly onto the curved face. Use a 4-1/2" PSA roll trimmed down to 3.5", or a sheet held on with double-sided tape or spray adhesive. Trim any overhang flush with the block's edges so it doesn't catch on the fretboard.
  2. Mark witness lines. Scribble a crosshatch pattern across the fretboard with a soft pencil. As you sand, the pencil disappears from the high spots first and remains in the low spots. When the crosshatch is gone everywhere, the block has reached the whole surface.
  3. Choose your starting grit. 80–120 for new fretboards or refret prep where there's wood to remove. 220 if the board is already close, including a board coming off the Fretboard Radius Jig, and you're cleaning it up. 320, 400, and higher for finishing.
  4. Sand lengthwise with even pressure. Hold the block flat to the fretboard and stroke along the length of the fretboard, nut to heel and back. Keep the block square. Do not twist or rock side-to-side. Twisting changes the radius.
  5. Re-mark and check often. Refresh the crosshatch between grits and confirm the block is touching the full surface before stepping up.

Notes

  • Verify the radius at every grit with a radius gauge. Twisting or uneven pressure can shift the profile, and catching it early means a few extra strokes instead of starting over.
  • Clean the fretboard between grits with a vacuum, brush, or compressed air. Leftover coarse grit will gouge the surface when you step up to a finer paper.
  • The 4" length is best for spot leveling and smaller corrections. The 8" and 10" cover the full board faster with a more consistent stroke.
  • Change or clean paper often. Loaded paper cuts unevenly and inefficiently.

FAQ

Which five radii should I choose?

You are picking five. A spread of 7.25", 9.5", 12", 16" and 20" covers vintage through modern through shred on both instruments without leaving a gap. If you know you will never do a vintage build, swap the 7.25" for a 10" and you get tighter coverage in the middle where most builds sit.

Here is how they map to real instruments.

  • 7.25" Vintage Fender. Pre-1983 Strat and Tele, and vintage P and J Bass. The fussiest to set up, since notes will choke on bends unless the action stays a little higher.
  • 9.5" The modern Fender standard on both guitar and bass. If you only ever used one radius, this is it.
  • 10" PRS and some Music Man.
  • 12" Gibson. Les Paul and SG, and most modern four and five string basses.
  • 14" Modern Fender Ultra and Charvel.
  • 16" The shred end. Ibanez, Jackson, Schecter, and modern five and six string bass.
  • 20" Very flat. Extended range guitar and flat modern bass.

Metric 400mm and 430mm are also stocked, and we cut custom radii at no extra charge. Tell us the number.

 

Do I need the 3.5" width?

Only if you are working on wide boards. Five and six string bass, extended range guitar, and wide multiscale necks. For standard guitar and four string bass the 2.75" blocks are the right size and cost less.