4dimk / prusa-mini-bear-z10-mod

Bear mod for Prusa MINI(+) for 10mm Z rods

Prusa-MINI-bear-mod-Z10

Table of Contents

1. Introduction
2. Features
3. Background
4. Disclaimer
5. Post MK4 release thoughts
6. BOM
7. Manual
8. Firmware
9. Print profiles
10. License
11. Credits and Inspiration

Introduction

Bear mod adaptation with MK3S print-head for Prusa MINI(+). Based on 10mm Z rods.

Features

• Compatible with Prusa MINI and MINI+
• Supported (dual) Z-axis based on the stock 10mm rods
• MK3S printhead w/ Filament Sensor
• Reuse of as many non-printed parts as possible¹
• Increased frame robustsness
• Maintenance friendly
• Reduced noise levels
• Compatible with stock firmware (with few limitation, see Firmware section)
• Open-source

Background

There are quite a few models and tutorials online (mainly in Printables) to build your Prusa Mini Bear mod, but as soon as you try to dive into versions and part compatibility, it becomes chaotic. Before printing, I wanted to ensure that all parts are well aligned and compatible with each other, but as far as I could find, there was no published CAD version with a complete model. Either I had to make a collection and hope for the best, or work on my own remix.

Main issues I observed:

• X and Y belts not running parallel to the axis.
• No stock Prusa extruder R6 version with proper probe offsets.
• No CAD with 10mm Z rods to verify.
• Z rods where not properly aligned with X axis holders and top Z brackets.

To fix these, I did the necessary modifications to the Fusion 360 designs I could find (see credits), as well design several parts from scratch.

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For the extruder, I started from the stock part as released by Prusa Research: https://github.com/prusa3d/Original-Prusa-i3

Parts that are not modified:

• Y-rod-holders, Y-idler-tensioner, 2040-end-caps (gregsaun) and cable clips: Link

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Disclaimer

The Original Prusa MINI(+) is an amazing little printer and as far as I am concerned the print quality is incredible for the price and ease of use. I chose to proceed with this build because as many others, I enjoy tinkering with 3D printers towards the possibility of improvement. In this case, towards a possibly more robust frame, which would (in theory at least) allow to maintain the same quality at higher accelerations with a direct-drive extruder to ease printing of flexible filaments. Keep in mind, as with any DYI assembly, there is always a chance of the final produced print quality to suffer, as it depends on the sourced hardware quality, part design and on the actual skills and experience put into building.

Post MK4 release thoughts

• From the mechanical side it appears that the MK4 X axis + Nextruder combo (assuming it will be sold separately) should be directly applicable in this mod, due to the 10mm Z rods.
• Firmware wise, significant modifications may be needed for the automatic layer calibration and load-cell interfacing.
• Input shaping: At the time of writing, I am not aware of how to connect an accelerometer to the MINI Buddy board.

Print settings

Assuming a Prusa MINI(+) is used, all parts are printed in PETG with the 0.2mm QUALITY@MINI profile. The only applied changes are:

setting	Value
Perimeters	3
Infill density	25%

One exception from PETG is the print-head fan-shroud which is printed in ABS, using the same print settings.

BOM

To do

Manual

The following guides should provide most of the necessary steps. If there is further interest I will make another document for more specific details.

• Frame, Y and Z axis: Bear Lab Guides
• E axis: Prusa MK3S assembly guide
• Z stepper motor in-series connection: Split-Z-axis-for-MINI by 3DPGVA
  • The color coding matches the original Prusa MINI extruder motor. Follow it closely.
• Electronics: Prusa MINI electronics assembly - Step 19 for the overview of BUDDY board connections.

Firmware

The goal of this mod is to make it compatible with the Original Prusa MINI(+) firmware, as to avoid the effort of maintaining a custom version.

Although the printer works directly after the mod, few features implemented at firmware level, are not compatible. Mainly, the load/unload scripts from the Filament section of the MINI screen.

Instead of using those, custom macros shall be used to perform load and unload filament actions. See Print profiles section.

The shortcoming is that these macros cannot be used while a job is running. If the filament runs out during a print, the factory default load/unload macros will be executed. That is fine for the unload function, but for the load phase I suggest to proceed as instructed in the screen but without actually inserting the filament to the extruder (only enough to register the filament with the sensor). Then only push the filament during the purging phase.

Factory provided modifiable settings

To properly use the MK3S printhead the following settings need to be changed directly from the MINI screen.

Hint: The menu to change these is kind of hidden; to access select:

Settings->HW Setup (Long press until sound):

setting	Value
Z-axis length	210
Extruder steps per unit	140
Extruder dir	Wrong

Save and return.

Print profiles

Under construction

Current draft versions under the PRINT_PROFILES folder.

Important: Make sure the any setting related to extrusion does not derive any values from the default MINI profiles. Even better, the MK3S settings are a good starting point.

In PrusaSlicer:

• Printer Settings->Notes: Make sure -PRINTER_MODEL_MINI- is changed to another value.
• Filament Settings->Custom gcode: Now that the printer name is changed, no bowden tuned values are applied. Since we use the MK3S extruder for this version. It is a good idea to copy-paste the settings from the equivalent MK3S filament profile.
• Filament Settings->Dependencies: Same as above.

All of these are implemented in the exported config bundles within this repo.

License

All parts are licensed under the GNU GENERAL PUBLIC LICENSE, Version 3. For more details please check the LICENSE file.

Credits and Inspiration

• Prusa Research for all their contributions to the 3D printing community and open-source 3D printers.
• Grégoire Saunier for his work on the Prusa MK3S upgrade, including the Bear X axis. Additionally, credits are given to the original developers of the projects and products as cited by Grégoire Saunier. This readme file structure is also inspired by the same repo.
• 3DPGVA for his Bear adaptation for Prusa MINI and Buddy board case.
• Tomson for providing the 10mm Z idler source files I started with.

Footnotes

1. Z rods are the only non-printed hardware part that will need to be modified and cut to length (311mm). ↩