Prusa i3 MK3S(+) Top Shelf & Bracket

Filament Dry-Box Shelf for Prusa MK3S+ (Frame-Mount)

This shelf mounts to the top rail of a Prusa MK3S+ frame and holds three

cereal-container filament dry boxes (~5 kg) directly above the printer, so

filament feeds straight down to the extruder. It is a combination of a

remixed frame bracket and a vibe coded two-piece tray.

Adapted to make sure there's no collision with the z-axis. Also angle

adjustable with M3 screws.

Files

Two 3mf files, both arrive pre-plated with the profile they

were printed on. Slice and go, or export STLs if you use another slicer.

`top_shelf_and_cover.3mf` (7 objects)

| Object | Size (mm) | Qty | Notes |

|---|---|---|---|

| `shelf_left` / `shelf_right` | 190.5 x 230 x 18 | 1 each | Tray halves, waffle-ribbed deck, 10 mm lip, glued at the seam |

| `dovetail_key` | 24 x 16 x 4.8 | 3 | Seam alignment keys |

| `cover_left` / `cover_right` | 187.05 x 223.4 x 0.6 | 1 each | Optional drop-in sheets that cover the rib waffle |

`Prusa_mk3s_top_shelf_support_x4.3mf` (1 object, 4 parts)

| Object | Size (mm) | Qty | Notes |

|---|---|---|---|

| Frame bracket | 56.1 x 105.21 x 10 | 4 | Remixed with M3 pilot holes added, lay-flat, no supports |

All four brackets are a single object in the project, so they plate and

slice as one print.

Components

• 8 x M3x6 screws to attach shelf to brackets
• 4 x M3x8 screws to adjust angle of brackets
• Superglue (tray seam + keys)

Print notes

Both projects use the same profile, and it is embedded in each `.3mf`, so

you do not need to set any of this by hand.

| | Tray, covers, keys | Brackets |

|---|---|---|

| Layer height | 0.3 mm | 0.3 mm |

| First layer | 0.3 mm | 0.3 mm |

| Perimeters | 4 | 4 |

| Top / bottom layers | 4 / 4 | 5 / 5 |

| Infill | 10 % grid | 10 % gyroid |

| Nozzle / bed | 205 °C / 60 °C | 205 °C / 60 °C |

| Filament | Sunlu PLA+ Black | Sunlu PLA+ Black |

| Supports | None | None |

Nozzle 0.4 mm, 0.45 mm extrusion width, no brim, on an Original Prusa i3

MK3S+ throughout.

Don't recommend below 4 perimeters. The deck ribs measure 3.57 mm thick.

Four perimeters at 0.45 mm lay down 3.60 mm of shell, which makes the ribs

print completely solid. Three perimeters only reach 2.70 mm and leave a

0.87 mm sparse core running down the center of every rib, which costs about

11 % of the tray's bending stiffness. The perimeter count matters far more

here than the infill percentage according to Claude.

Printing in regular PLA instead of PLA+

Regular PLA is fine, and is marginally stronger in this application.

I later found out that PLA+ is not the stronger material for this use case. It

trades tensile strength and stiffness for impact toughness. SUNLU's own

data sheets list 61 MPa for their regular PLA against 46 +/- 5 MPa for PLA+ 2.0.

Since this shelf carries a static load and never gets impacted, the

toughness PLA+ buys you isn't doing much. Regular PLA has slightly more

margin. Either works well, i just had extra PLA+ lying around.

Assembly

• Tray halves glue together with the dovetail keys dropped into the seam

pockets

• Brackets clip over the frame's top rail at centers 5 / 87 / 169 / 251 mm

across the span, matching the tray's screw-hole columns

• The tray sits on the brackets and screws down through the counterbores

into the bracket pilot holes

• The 2.6 mm pilot holes take M3 screws directly (self-tapping); no

drilling needed

• Each tray half is screwed to two brackets independently, so the glue seam

is not the main load path

• Assemble the shelf and screw in the brackets before sliding the whole

thing into place on your Prusa

Notes

• The full setup adds ~5.7 kg on top of a bed-slinger; the frame handles

it, but some extra ringing on tall prints is possible

• Sized for three boxes; a four-box version would need a wider shelf than

the bracket span can properly support

• Shelf vibe coded with Claude Code

Possible improvements

• Hook-on tool caddy for the rear/side lip
• Box dividers / anti-slide stops that clip over the lips

Model origin and license

Bracket remixed from

Prusa i3 MK2(s) & MK3 Spool Holder - Frame Mount - Top Loader

by MartinMajewski, licensed

CC BY-NC-SA.

This model is published under the same CC BY-NC-SA license (ShareAlike

requirement of the original).