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Voron Nevermore Filter — Complete Guide to VOC and Odor Control

Mod Enclosure Safety

Printing ABS on your Voron produces volatile organic compounds (VOCs) — primarily styrene, which gives ABS its distinctive sweet chemical smell. While an enclosure contains these fumes, it doesn't remove them. Open the door after an 8-hour ABS print and you're hit with a concentrated burst of VOCs. The Nevermore filter solves this by recirculating enclosure air through activated carbon, continuously scrubbing VOCs throughout the print. This guide covers everything: why VOCs matter, Nevermore versions, carbon types, fan selection, and Klipper configuration. Last updated: May 2025.

Why VOCs Matter

ABS filament is about 60% styrene monomer by mass. During printing, a fraction of this styrene is released as vapor. Studies have shown that ABS printing can produce VOC concentrations of 500-2000 ppb (parts per billion) inside an enclosure — well above the 20 ppb odor detection threshold and approaching occupational exposure limits for long print sessions.

The primary VOCs emitted during ABS printing include:

Activated carbon filtration is the most practical way to reduce VOC concentrations inside your enclosure. Unlike HEPA filters (which only trap particles), activated carbon adsorbs gas-phase VOCs through a process called physisorption — the VOC molecules are trapped in the porous structure of the carbon.

Nevermore Design Philosophy

The Nevermore is a recirculating filter designed specifically for Voron enclosures. Unlike exhaust fans that vent air outside (which wastes heated chamber air and pulls in cold, dusty air from the room), the Nevermore recirculates enclosure air through a carbon bed and returns clean air back into the chamber.

The key design features:

Nevermore V5 vs V6

The Nevermore has gone through several revisions. The two most common versions are V5 and V6:

Nevermore V5

The V5 design uses a cylindrical carbon bed with a 5015 axial fan pushing air through the center. Air enters the center of the cylinder, passes radially outward through the carbon bed, and exits through the outer wall. Key specs:

Nevermore V6

The V6 improves on the V5 with a dual-chamber design that doubles the carbon volume and improves airflow. Key differences:

For most Voron V2.4 and Trident builds, the V6 is recommended for larger enclosures with higher air volume. The V5 works well for V0.2 and smaller builds where space is at a premium.

Build Instructions

Building a Nevermore requires 3D printed parts, a fan, activated carbon, and some filter foam. Here's the general process:

  1. Print the parts: Download the STL files from the Nevermore GitHub repository. Use ABS or ASA filament — PETG may soften at typical Voron enclosure temperatures (50-65°C). Print with 0.4mm nozzle, 0.2mm layer height, 4 walls, 40% infill for structural parts
  2. Prepare the carbon: Crush and sieve pelleted activated carbon to the recommended mesh size (typically 1-3mm granules). Remove dust by shaking through a fine sieve — carbon dust will blow through the filter and coat your enclosure
  3. Assemble the body: Press-fit or screw the main body components together. Ensure the air channels are clear and the fan mounting surfaces are flat
  4. Add filter foam: Place a layer of open-cell foam (2-3mm thick) at the carbon inlet and outlet to prevent carbon dust from escaping
  5. Fill with carbon: Fill the carbon chamber with prepared activated carbon. Tap the assembly gently to settle the carbon — do not pack it tightly or airflow will be restricted
  6. Install the fan: Mount the 5015 fan with the airflow direction matching the arrow on the housing. Use M3x8 or M3x10 screws
  7. Mount in enclosure: Secure the Nevermore inside your Voron enclosure. Common locations: rear panel (above the electronics bay), side panel, or top panel. Ensure the intake is clear of obstructions

Carbon Types and Selection

Not all activated carbon is created equal. The type of carbon significantly affects VOC adsorption performance:

Recommended source: Activated carbon designed for aquarium filters or HVAC air purification. Avoid BBQ charcoal or carbon designed for water filtration — these are optimized for different pore sizes and won't effectively trap VOCs.

Fan Selection — 5015 Axial vs Blower

The Nevermore was designed around 5015 axial fans, specifically:

Regardless of fan type, use a 24V fan if you can — 12V fans need higher current to deliver the same power, and most Voron power supplies are 24V. Wire the fan to a controllable fan port on your mainboard (e.g., FAN1 or FAN2 on BTT Octopus) so Klipper can vary the speed.

Klipper Configuration

Configure the Nevermore fan as a controller_fan in your printer.cfg so it can be controlled via macros or temperature-triggered rules: 


[controller_fan nevermore_fan]
pin: PD12  # Adjust for your board
max_power: 1.0
kick_start_time: 0.5
off_below: 0.1

For variable speed control based on chamber temperature (run faster when it's hotter, since VOC off-gassing increases with temperature): 


[gcode_macro NEVERMORE_SET_SPEED]
gcode:
    {% set SPEED = params.SPEED|default(0.5) %}
    SET_FAN_SPEED FAN=nevermore_fan SPEED={SPEED}

[gcode_macro NEVERMORE_AUTO]
gcode:
    {% set CHAMBER_TEMP = printer.temperature_sensor.chamber_temperature.temperature %}
    {% if CHAMBER_TEMP >= 45 %}
        SET_FAN_SPEED FAN=nevermore_fan SPEED=1.0
    {% elif CHAMBER_TEMP >= 30 %}
        SET_FAN_SPEED FAN=nevermore_fan SPEED=0.6
    {% else %}
        SET_FAN_SPEED FAN=nevermore_fan SPEED=0.3
    {% endif %}

Integrate Nevermore auto-speed into your PRINT_START and PRINT_END macros: 


[gcode_macro PRINT_START]
gcode:
    {% set BED_TEMP = params.BED|default(100) %}
    {% set EXTRUDER_TEMP = params.EXTRUDER|default(250) %}
    
    M140 S{BED_TEMP}
    M104 S{EXTRUDER_TEMP}
    
    G28
    QUAD_GANTRY_LEVEL
    G28 Z
    BED_MESH_CALIBRATION ADAPTIVE=1
    
    M190 S{BED_TEMP}
    M109 S{EXTRUDER_TEMP}
    
    NEVERMORE_AUTO  # Start filter based on chamber temp

Or simply run the Nevermore at full speed during the entire print: 


[gcode_macro PRINT_START]
gcode:
    # ... (standard PRINT_START content) ...
    SET_FAN_SPEED FAN=nevermore_fan SPEED=1.0

[gcode_macro PRINT_END]
gcode:
    SET_FAN_SPEED FAN=nevermore_fan SPEED=0
    # ... (standard PRINT_END content) ...

Carbon Refill Schedule

Activated carbon has a finite adsorption capacity. Once all the pore sites are filled with VOC molecules, the filter stops working and can even re-release captured VOCs. Refill schedule recommendations:

To extend carbon life, run the Nevermore for 15-30 minutes after a print finishes to continue scrubbing residual VOCs from the enclosure air. Store spare carbon in an airtight container — activated carbon adsorbs moisture and VOCs from ambient air, degrading its performance before you even use it.

Alternative: Bento Box

The Bento Box is a popular alternative to the Nevermore. It uses a different form factor — a flat rectangular carbon bed with dual fans — and mounts differently inside the enclosure. Key differences:

Both the Nevermore and Bento Box are effective. The Nevermore is more compact and easier to integrate into smaller Voron builds (V0.2, Switchwire). The Bento Box offers higher airflow and is better suited for larger enclosures (V2.4 350mm, Trident 300mm+). Choose based on your available space and airflow requirements.

Final Recommendations

A Nevermore filter is one of the highest-value mods you can add to your Voron. It dramatically reduces VOC exposure, eliminates the chemical smell in your printing space, and costs under $20 in materials. For anyone printing ABS regularly, it's not optional — it's essential.

Need Parts?

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