The Prusa i3 MK3S to Bear upgrade is a significant modification that enhances the printer's rigidity, speed, and overall performance. Here's a general overview of the process:  

1. Choose Your Upgrade Path:

• Half Upgrade: This focuses on upgrading the frame to the MK3S+ style, improving stability.
• Full Upgrade: This includes all the elements of the Half Upgrade plus a redesigned Z-axis for increased strength and smoother movement.

2. Gather Necessary Parts:

• Bear Upgrade Kit: This typically includes most of the required components like:
  • Anodized Aluminum Extrusions: Replace the original frame.
  • Printed Parts: 3D-printed components specific to the Bear upgrade. ¹  
    1. Bear Upgrade for Prusa (i3) MK4(S), MK3.5(S), MK3.9(S) - Printables.com

    

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  • Hardware: Screws, nuts, bolts, etc.
• Additional Components (may be required depending on your chosen upgrade):
  • Z-axis upgrades: If doing a Full Upgrade, you'll need components for the new Z-axis design.

3. 3D Print Required Parts:

• Print Settings: Use high-quality settings (e.g., PETG filament, multiple perimeters) for optimal strength and durability.  

4. Disassemble Your Original Prusa MK3S:

• Carefully document the process: Take pictures and notes throughout disassembly to aid in reassembly.

5. Assemble the Bear Frame:

• Follow the provided instructions: These are usually available in the Bear Upgrade kit or online resources.
• Align components precisely: Ensure proper alignment and fit of all parts.

6. Install Electrical Components:

• Reinstall electronics: Connect all necessary wiring to the new frame.

7. Reassemble the Printer:

• Mount the extruder, hotend, and other components: Refer to your original Prusa MK3S manual for guidance.

8. Test and Tune:

• Perform test prints: Check for any issues and fine-tune the printer's settings as needed.
• Adjust tensioners: Properly tension all belts for optimal performance.

Important Considerations:

• Technical Skills: This upgrade requires some mechanical and technical skills.
• Time Commitment: The process can take several hours or even days depending on your experience level.
• Cost: The Bear Upgrade kit and any additional components will incur costs.
• Resources: Refer to the official Bear Upgrade documentation and online communities for detailed instructions, troubleshooting, and support.

Disclaimer: This is a general overview. Always refer to the specific instructions and guidelines provided with your chosen Bear Upgrade kit.

Note: The "Bear" upgrade often refers to modifications inspired by the Prusa i3 MK3S+ design. It may not be an officially supported or branded upgrade.

By following these steps and carefully considering the requirements, you can successfully upgrade your Prusa MK3S to a Bear-style configuration, potentially improving its performance and aesthetics.