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YOU CAN BUILD A 3D PRINTER THAT PRINTS UPSIDE DOWN AND FOLDS INTO A FILAMENT BOX

A 3D printer that prints upside down, folds flat, and fits inside a filament box when you are done.

by Audiotronix

FULL CAD BOM FIRMWARE DOCS

WorkshopOpen-hardware

Built withRaspberry Pi3D printing

difficulty
●●●●○
time
two weekends
license
GPL-3.0
repo
repo INACTIVE SINCE 2023343 stars

WHAT YOU’LL NEED

1
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COMPAREE VERDICT

Positron LT is the RepRap version of KRALYN's Positron V3: the structural parts are 3D printed instead of CNC-machined, so you can build it with an ordinary printer and parts from normal suppliers. The form factor is strange and clever — the print bed is a heated glass sheet above the nozzle, the part prints hanging underneath, and the whole machine folds up small enough to fit inside a filament box. The payoff is portability; the cost is that you are building a machine with about 35 printed parts, Makerbeam extrusions you cut to length, an integrated 200 W power supply and GT2 belts on X and Y, and the documentation is unfinished. The BOM with prices and links and the STL/STEP files are there, but the assembly page stops after the cutting list ('images coming soon') and the software page is an empty work-in-progress stub, and the repository has not changed since September 2023. You will be relying on the Discord, photos and your own experience. This is a clever second-printer build for someone who has built a printer before and is comfortable improvising around gaps in the instructions. If you need a polished assembly manual, this is not it.

GOOD TO KNOW

  • —Bill of materials, STL files and a STEP model are published. Dual licence: GPLv3 for personal, educational and non-commercial use; commercial use needs the separate commercial licence (small royalty).
  • —Assembly documentation stops after the tool list and cutting plan; there are no wiring diagrams, so expect to rely on the community Discord and photos.
  • —The README still calls it a work in progress, but the repository has not changed since September 2023 — some docs pages (assembly images, software) were never finished.
  • —You need an existing 3D printer to make the structural parts (about 35 pieces); no machining, but Makerbeam extrusions and linear rails have to be cut to length and some holes drilled.
  • —No video assembly guide from the creator, and none is linked in the repository.
  • —Design by Audiotronix, based on the original Positron V3 by KRALYN, which required machined parts and exotic Synchromesh wire.

Parts to buy

8 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • 10×10 Makerbeam extrusionsFind
  • Three pancake NEMA 17 steppersFind
  • 3 mm GT2 beltsFind
  • MGN9/MGW9/MGN12 railsFind
  • Funssor hotendFind
  • SKR Pico plus Raspberry Pi Zero 2WFind
  • Muon3D heated glass bedFind
  • Meanwell EPP-200 PSU built into the baseFind

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Can I build this?

Printabout 35 printed pieces (32 different parts) — base parts and covers, motor brackets, belt tensioners, bed holder, side panels — all provided as STL and STEP in the repository
Buy10×10 Makerbeam extrusions, three pancake NEMA 17 steppers, 3 mm GT2 belts, MGN9/MGW9/MGN12 rails, a Funssor hotend, SKR Pico plus Raspberry Pi Zero 2W, Muon3D heated glass bed, and a Meanwell EPP-200 PSU built into the base
Toolsan existing 3D printer, a saw for aluminium and steel (to cut Makerbeam and rails), a drill, a screwdriver, a soldering iron, optionally a tap; plus the community Discord for troubleshooting
Skillsintermediate-to-advanced FDM building — you need to be comfortable with Klipper, belt tensioning, and working from incomplete instructions
Timetwo weekends if you have built a printer before and the parts print cleanly; longer if this is your first CoreXY or you hit a hardware revision mid-build
Cost$$$, dominated by the motion components (linear rails, belts, steppers), the hotend, and the controller board
Safetystandard mains voltage PSU and soldering; no unusual risks beyond ordinary electronics care

This build involves mains voltage — for adults comfortable with electrical work only.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

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Gallery

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the README and the work-in-progress disclaimer (The project is openly marked as evolving; check for recent commits before ordering parts.)
  2. 2.Download the BOM spreadsheet and verify part availability(The BOM lists links and prices for every part (Makerbeam is cut to length, by you or by Makerbeam); the Muon3D heated glass bed is marked highly recommended, and the hotend entry says it will be replaced by a Phaetus hotend.)
  3. 3.Print the structural parts on your existing printer(About 35 pieces; print in a stiff, heat-resistant technical filament — the repo lists ASA and PC Blend Carbon Fiber as tested.)
  4. 4.Join the community Discord for assembly support(The README links the project Discord directly: discord.gg/HJ44ZeGG2F.)

KNOWN ISSUES

  • Assuming the documentation is complete — it is not. The BOM and STLs are there, but assembly steps rely on photos, Discord threads, and your own experience with CoreXY printers.
  • Ordering parts without checking the BOM notes — a few parts are still marked WIP and the hotend entry was never updated after 2023; ask on the Discord which hotend people actually use.
  • Printing the structural parts in PLA — the repo recommends a stiff, heat-resistant technical material; ASA and PC Blend Carbon Fiber are the tested ones.
  • Expecting a ready firmware config — the Software page is still an empty work-in-progress stub, so you will have to write and tune your own Klipper config for the SKR Pico and Raspberry Pi Zero 2W, or get one from the Discord.
  • Building this as your first 3D printer — you need an existing printer to make the parts, and the assembly expects you to know what a properly tensioned GT2 belt feels like.
  • Underestimating print time — the BOM lists about 35 printed pieces and roughly 58 hours of print time (PrusaSlicer estimates for a Prusa Mini), and any failed print adds to the schedule.

Can I buy a kit?

No. This is a self-sourced build; you print the structural parts and order the motion components, electronics, and PSU yourself from the BOM.

What is the print volume?

180 × 180 × 180 mm, per the specs in the README — with a footprint of about 200 × 200 mm.

Why print upside down?

The inverted layout is what lets the machine fold up small enough to fit inside a filament box — the defining idea of the original Positron V3 that LT keeps.

Which hotend does it use?

The BOM lists a complete Funssor hotend and notes it was meant to be replaced by a Phaetus one — confirm in the Discord before substituting.

What changed from the original Positron V3?

LT replaces CNC-machined parts with printed ones, swaps Synchromesh wire for standard 3 mm GT2 belts, integrates a 200 W PSU, and reduces the part count. The folding mechanism and upside-down print layout are the same.

Community builds

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Discussion1

FROM THE COMPAREE TEAM

The whole machine folds flat and fits inside a standard filament box — portability no normal printer offers. Would you actually travel with this, or is the appeal just desk space when you are not printing?

CompareeTEAM1mo agoedited

Practical notes from our verification: the README still calls this a work in progress, but the last push to the repository was in September 2023, so do not expect ongoing updates — several parts are still marked WIP and the BOM says the Funssor hotend will be replaced by a Phaetus hotend when available. The repo has a full parts list (BOM) with prices and links, STL and STEP files for around thirty printed parts, a short Assembly page (tools and cutting plan) and a Software page that is still an empty stub, and a Discord server is linked right at the top of the README for the questions the docs leave open. The frame is 10×10 Makerbeam extrusion with printed structural parts, MGN rails, an SKR Pico and a Raspberry Pi Zero 2W, and the build volume is 180 × 180 × 180 mm. Licensing is dual: GPLv3 for personal, educational and non-commercial use, and a separate commercial licence with a royalty if you want to sell printers. KRALYN created the original Positron V3 that this design is based on. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

Audiotronix

Audiotronix designed Positron LT as a RepRap-friendly version of KRALYN's Positron V3, replacing the original's CNC-machined parts and exotic Synchromesh wire with 3D-printed components and standard GT2 belts. The goal was to make the folding, portable form factor accessible to anyone with an existing FDM printer and parts from ordinary suppliers.

GitHub

Star the project on GitHub

DISCLAIMER

  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
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