Prusa's official manual is ~350 steps across 8 chapters. This guide distills every chapter into plain-language steps, a difficulty & time rating, the exact parts you'll need, and the pro-tips & mistakes that actually matter — plus an original diagram of the one part everyone gets wrong: the CoreXY belt path.
Eight chapters, built bottom-up. Each becomes a sub-assembly that clicks into the next. Nothing is glued or welded — every step is reversible, which is exactly why a full teardown-and-rebuild is realistic. Difficulty is rated 1–5; times are first-timer estimates.
Golden rule from the manual: sort your fasteners into labelled trays before you start (builders use 12–14), work on a spinnable surface, and never return hardware to bags mid-build. The kit includes a spare-parts bag — if you drop an M3 nut into the carpet void, don't panic.
All included in the kit (box: 2 · Electronics & Fasteners). The one upgrade worth making: use the real T10 Torx driver, not the flat orange multi-driver — builders report the flat one strips both the screws and itself.
Prusa names every screw by thread, length & head. Learn these six and the whole manual reads easily. Format: M3 × 10 rT = 3 mm thread, 10 mm long, ridged T-head.
Other suffixes you'll meet: sT self-tapping (cuts its own thread), r plain ridged head, 6-32 imperial power-terminal screws (heatbed/PSU), and Nylon rivet push-pins for the sheet-metal panels (50 across the build).
Tap any chapter to expand its plain-language walkthrough, parts, tips and gotchas. They're ordered exactly as you'll build them.
CoreXY uses two separate open GT2 belts. Both motors stay bolted to the rear corners; the belts do all the moving. The single rule that prevents 90% of mistakes: the X-motor belt runs in the UPPER lane, the Y-motor belt runs in the LOWER lane. Each belt end clamps into the print-head holder with 4–5 teeth sticking out.
Schematic, not to scale. Follow Prusa's Step 45 "XY belts INFO" illustration for exact pulley wraps. The takeaways this diagram locks in: two independent loops, upper=X / lower=Y, motors fixed at the rear, both ends terminating at the centre print head.
Tension is set later, in Calibration. Leave the M3x30 tensioner screws just 3–4 turns in during assembly. Final tuning uses the firmware wizard: left screw = upper (X) belt, right screw = lower (Y) belt, target ≈ 96 Hz upper / 92 Hz lower, adjusted ½-turn at a time, alternating sides to keep the gantry square.
With the build done, four things turn a box of parts into a calibrated CORE One+.
Copy the latest firmware to the USB drive and update. This version is required for the "+" — it adds Chamber Vent Control.
Settings › Hardware › Chamber Vent Control › Auto. The Nextruder now opens the grille for PLA/PETG, closes it for ABS/PC-CF — the core "+" feature.
Run first-layer calibration (loadcell auto-probes the sheet), then the belt-tuning & input-shaper routines. Set belt tension to the 96/92 Hz targets.
Print the sample from the USB drive. Watch the first layer; a clean, evenly-squished first layer means your rebuild is dialled in.
Pair this guide with your BOM workbook. The Excel checklist tracks every printed part and fastener as you reprint/buy and install — work the two side by side.
Distilled from Prusa's official CORE One+ kit assembly manual (v2321) and Knowledge Base, verified July 2026.