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TuneFast Harp, a 3D-printed harp
Image: makefast via Thingiverse, CC BY-SA 4.0
Strings · Harp

TuneFast Harp

An 8-note diatonic harp made from one string wound over bearings, for under $7

Designed by makefast, published on Thingiverse

CC BY-SA 4.0 Commercial use OK Build info 4/5

Licence verified on Thingiverse, 20 October 2026.

Get the files on Thingiverse ↗ Watch the video
Notes
8, diatonic, from a single string
Cost
Under $7 in hardware, per the designers
Print
About 3 hours, ~100 g PLA, at least 30% infill
String
Nylon guitar string or fishing line (or a thin metal string)
Difficulty
Easy; aimed at classrooms
On Thingiverse
3,590 likes · 49 comments (as of 20 Oct 2026)

About the TuneFast Harp

One string zig-zags over eight V-groove bearings, and each stretch between bearings gives a different note, making an 8-note diatonic harp. The makerspace that designed it wanted it cheap, quick to print and easy to assemble, so young makers sharing resources could build one as a classroom project. They put the hardware under $7 per harp, though many parts come in bigger packs, so it's worth making several.

It printed in about 3 hours on their printer at fast settings. Coarse layers are fine, but use at least 30% infill and a stiff plastic. PLA works well, while ABS is less stiff, which matters here. A newer base adds a parabolic reflector that focuses the sound 8–10 cm from the string, and a clipped corner saves material. Printable M3 washers and the end spacer cut the parts list further.

Clean any blobs that could catch the bearings. Then mount each bearing on an M3 × 20 bolt with a washer between bearing and plastic, tight but not rubbing. The highest note uses a spacer instead of a bearing. Their two videos compare a metal string with a nylon one. Don't over-tighten a metal string.

What you'll need

Printed parts

  • Harp base (the newer version has a sound reflector)
  • Optional: 9 M3 washers and the M3 end spacer

Bought parts

  • 1 right-handed guitar tuner
  • 9 × M3 × 20 bolts and nuts
  • 8 × 3×12×4 mm V-groove bearings
  • 1 nylon guitar string (or 25–50 lb fishing line, or a 9–17 gauge metal string)
  • Optional: an M3 6×4 spacer and 9 Belleville washers

Tools

  • Screwdriver and spanner
  • A tuner

Build overview

  1. Print. Print the base in PLA with at least 30% infill; coarse layers are fine.
  2. Clean up. Remove strands or blobs near the bearing positions.
  3. Fit the bearings. Mount each on an M3 × 20 bolt with a washer between bearing and plastic.
  4. Fit the spacer. Fit the end spacer for the highest note.
  5. String and tune. Check the bearings spin freely, fit the tuner and string it, then tune.

Print settings

  • Material: PLA or another stiff filament
  • Infill: At least 30%
  • Layers: Coarse/fast is fine
  • Time: About 3 h

Videos

Play video: TuneFast Harp with a metal string (loads YouTube)
TuneFast Harp with a metal string, Makefast Workshop (the designers). Plays from youtube-nocookie.com after you click.
Play video: TuneFast Harp with a nylon string (loads YouTube)
TuneFast Harp with a nylon string, Makefast Workshop (the designers). Plays from youtube-nocookie.com after you click.

Nothing loads from YouTube until you press play. Video thumbnails are © their creators.

Photos

Thingiverse doesn't let us fetch its gallery, so the photos stay on Thingiverse. See them on Thingiverse ↗

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