SideDock MMU3 — Compact Vertical Mount for Prusa CORE One/+/G2

Overview

SideDock MMU3 is an original side-mounted holder that installs the MMU3 vertically on the right side of a Prusa CORE One/+/G2. It creates a compact, accessible setup that keeps the MMU3 easy to reach without accessing it from above or behind the printer

Designed as an alternative to top-mounted MMU3 layouts, SideDock keeps the space above the printer clear and reduces the rear clearance needed for the MMU3 and its PTFE tubing. Instead of mounting the MMU3 at the top rear like the Prusa MMU3 Lite configuration, it places the unit neatly alongside the printer. It also avoids the additional cost of the Prusa MMU3 Enclosed configuration and its replacement top cover.

SideDock uses a standard right-side Monkey Bar, which is required for installation. The upper mount hooks onto the Monkey Bar and carries the MMU3, while the lower support rests against the printer side panel to stabilize the assembly. The PTFE tube follows the right-side swing-arm path and can enter the enclosure through several routing options.

Included Models

The SideDock model includes two printed parts:

• SideDock-MMU3-Top.stl – Upper Monkey Bar hook and load-bearing MMU3 support

• SideDock-MMU3-Bottom.stl – Lower side-panel support that stabilizes the MMU3

Required Companion Model

Print the following part from Monkey Bars – Accessory Frame Bars for Prusa CORE One/+:

• Monkey-Bar-Standard-Right.stl – Required right-side mounting bar for SideDock
  

Required Hardware

SideDock Mounting

• 4x M3x10 screw – Secures the SideDock top and bottom parts below the MMU3

• 2x M3x8 screw – Secures the original MMU3 Label plate across the front of both SideDock parts

Monkey Bar Installation

• 2x M3x16 screw – Recommended length; M3x18 screws also fit

• 1x M3nN nyloc nut

PTFE Tube

• 1x PTFE tube, 4x2.5 mm, 950 mm long

In the SideDock setup, a PTFE tube of about 950 mm loaded filament reliably. The swing-arm path itself uses approximately 500 mm of tube; the remaining 450 mm forms a smooth curve from the swing arm to the MMU3 FINDA sensor. Remember to enter the tube length in the printer firmware.

Although the Prusa firmware allows loading distances up to 1000 mm, longer PTFE paths are increasingly sensitive to friction and tolerances. My experience, along with reports from other users, shows that loading reliability can decrease as the tube length approaches 1000 mm. When a fault occurs after the extruder engages the filament, the MMU3 may attempt to retract it toward the FINDA sensor, briefly placing both units under opposing load.

Be aware that PTFE tubes vary in internal diameter (e.g., 2.5 or 3.0 mm) and inner-channel bore shape (e.g., standard round or star-shaped). Together with couplers, Y-splitters, routing bends, and filament choice, these differences affect friction and loading reliability on longer paths.

Communication Cable

• 1x MMU3 communication cable for Prusa CORE One, 800 mm (80 cm) long

SideDock requires the longer 800 mm cable, not the standard shorter 450 mm cable.

The cable can be sourced from:

• Original Prusa cable — recommended:
  Original Prusa MMU3 Community Version Cable for CORE One
  https://www.prusa3d.com/product/original-prusa-mmu3-community-version-cable-for-core-one-3/

• Third-party cable — alternative:
  AliExpress MMU3 cable
  Select the CORE One 800 mm / 80 cm variant, not the other cable option.
  https://www.aliexpress.com/item/1005006813776775.html

Print Settings

• Nozzle: 0.4 mm

• Layer height: 0.20 mm

• Material: PETG

• Perimeters: 4 minimum

• Infill: 20% gyroid or grid

• Supports: Not required

• Brim: 7 mm, highly recommended for the tall top part (see Print Orientation below)

Print Orientation

Print SideDock-MMU3-Top.stl standing on its side.

The top part is a tall print. Do not lay it flat to reduce its height: the supplied orientation places the layer lines in the direction intended to carry the MMU3 load at the Monkey Bar hook.

Although this orientation may seem counterintuitive, no supports are required. A brim is highly recommended to improve bed adhesion and help keep the tall part stable throughout the print

Assembly

1. Install Monkey-Bar-Standard-Right.stl on the top-right side of the printer, following the Monkey Bars installation instructions.

2. Place SideDock-MMU3-Top.stl below the MMU3 and secure it with two M3x10 screws.

3. Place SideDock-MMU3-Bottom.stl below the MMU3 and secure it with two M3x10 screws.

4. Reinstall the original MMU3 Label plate across the front of both SideDock parts with two M3x8 screws.

5. Hook the completed SideDock assembly onto the right Monkey Bar. The release lock remains accessible from behind the MMU3.

6. Connect the 800 mm MMU3 communication cable by following Steps 21–25 of the Prusa CORE One setup instructions.

Continue with the PTFE Routing and Firmware Settings sections below.

PTFE Routing

Plan the PTFE route in three steps:

1. Choose how the tube is guided along the swing arm

2. Choose how the tube enters the printer enclosure

3. Set the PTFE length in the firmware and verify free movement

Step 1 — Guide the PTFE Tube Along the Swing Arm

The PTFE tube must move with the right-side swing arm without excessive sag, sharp bends, or interference with moving components.

• Option A — Standard Prusa Routing
  Use the original Prusa CORE One/+ Velcro retention system
  

• Option B — Guided or Structured Routing
  Use a solution that guides, supports, or controls the PTFE tube along the swing arm:

  • Anti-Sag Zip-Tie Solution with Single or Dual PTFE (my remix)

  • Prusa CORE One Swing Arm Cable/PTFE Brackets

Step 2 — Bring the PTFE Tube Into the Enclosure 

Choose one enclosure-entry method independently from the swing-arm routing method.

• Option A — Open-Top Routing
  Remove the top panel and route the tube directly into the printer, as used by the Prusa MMU3 Lite configuration. This can be useful as a temporary solution, but it leaves the printer unenclosed
  
  

• Option B (Recommended) — Magnetic Top-Corner Routing

  • Prusa CORE One/+/G2 Magnetic Top Back PTFE Pass Through (my remix)
    
    

• Option C — Other Routing Models (untested)

  • CORE One MMU PTFE Tube Connector (No Drill) – Top-panel entry without drilling

  • MMU3 CORE One Top Acrylic Panel PTFE Filament Pass – Requires a hole in the acrylic top panel

  • Prusa CORE One MMU Top Cover PTFE Guide – PTFE guide integrated with a replacement top cover

Step 3 — Configure and Verify

1. Open Settings > Filament Sensors and confirm that the Side Filament Sensor is enabled. Keep it enabled even when it is not used by this installation, and do not insert filament into it.

2. Open Settings > Hardware > MMU and set the MMU-to-extruder PTFE tube length to 950 mm, or to the actual length used by your installation if it differs.

3. Move the swing arm through its full travel and confirm that the PTFE tube moves freely without tightening, snagging, or rubbing.

Feedback

If you make this model, feel free to leave a comment or share your feedback. I always enjoy seeing how it fits into different setups and how it performs in real use.