Black Spots on Print
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If you do not have a specific hotend for every material you are using, you will likely experience some black dots on your prints from time to time. Even when you are using only one material, this can still be a frequent occurrence. This can be from a few culprits, but often it will show itself by having built up material on or in your hotend.
One of the biggest issues with this failure is that you will often not be able to diagnose it until it happens. This means that a black spot might show up on an important section of your print 10+ hours in. This is why it is crucial you maintain the cleanliness of your hotend by frequently purging and cold pulling any residue from your nozzle, along with using a nylon brush and silicone sock.
Every hotend setup requires slightly different assembly methods, but nearly all necessitate avoiding over-tightening. As the heater increases in temperature, metal expansion can create minor gaps between the nozzle and heater block. These gaps may allow material to ooze out, potentially depositing onto prints. Since this material often remains on the hot nozzle before transferring to the model, it typically appears blackened and burnt regardless of the original filament color.
If the heater block becomes loose when heated or excess material accumulation on the nozzle/hotend occurs frequently, tightening these components may be necessary. Final tightening of the nozzle and heater block should occur when heated to 240°C or higher (for all-metal hotends), using appropriate gloves and tools to mitigate burn risks. Care must be taken to avoid over-tightening, as excessive force can fracture heater blocks, nozzles, or heat break barrels—especially when components are hot. Tighten only until components are secure and unlikely to loosen during operation.
Persistent material oozing between the nozzle and heater block often indicates worn or poorly manufactured components. Low-quality parts frequently exhibit thread tolerance issues, as evidenced by cross-sectional images of counterfeit products. To ensure proper fit and durability, purchase name-brand components from verified suppliers. For example, E3D hotends should be sourced exclusively from authorized distributors like E3D, Filastruder, or Matterhackers to avoid counterfeit products. Matterhackers serves as a reliable supplier for most 3D printing components.
Filament switching or post-extended printing sessions necessitate purging oxidized material from the hotend. Several methods achieve this:
Same Material Purging Heat the hotend to standard printing temperature, manually feed approximately one inch of filament, then retract swiftly. Trim the filament end and repeat for color changes to prevent cross-contamination.
Higher-Temperature Material Transition For materials requiring elevated temperatures (e.g., PLA to ABS), repeat the standard purge process multiple times. Color differences in higher-temp filaments make insufficient purging visually apparent, while increased heat typically clears residual material effectively.
Lower-Temperature Material Transition Switching to lower-temp materials (e.g., ABS to PLA) poses challenges, as residual high-temp material may remain. Standard purging often proves inadequate due to viscosity mismatches.
High-Risk Purge Method Extruding lower-temp filament through a high-temp hotend (e.g., PLA at 245°C post-ABS) requires rapid extrusion and immediate retraction. This approach carries elevated clog risks and may leave residual material.
Recommended Solutions
Cold Pull Method Detailed in subsequent instructions, this technique mechanically removes contaminants through controlled thermal cycling.
Cleaning Filament/Nylon Purge Heat the hotend to 240°C–250°C (or material-specific guidelines), extrude cleaning filament, and retract promptly. Observe extracted contaminants to verify effectiveness.
Residual Risk Even cleaning filaments may leave trace material that emerges later as burnt deposits. The cold pull method remains the most reliable contamination-removal technique.
Key Technical Notes
Oxidation Mitigation: Regular purging prevents carbonized material accumulation in heat zones.
Temperature Thresholds: Always reference material-specific glass transition temperatures when selecting purge parameters.
Nozzle Protection: Abrupt temperature changes during purging risk thermal shock; maintain consistent heating during procedures.
When transitioning to lower-temperature printing materials, cold pulls serve as the recommended maintenance procedure. This method also provides routine hotend cleaning benefits regardless of material changes.
Cold Pull Methodology
Material Selection
Preferred Options: Nylon-based filaments (e.g., Nylon 910) or dedicated cleaning filaments
Alternative: Filament matching the material being cleared
Heating Phase
Heat hotend to the cold-pull material’s printing temperature (250°C for Nylon 910)
Extrude material until previous filament residue ceases emerging from the nozzle
Cooling Protocol
Rapidly reduce hotend temperature to 130°C–150°C (130°C optimal for residue removal)
Avoid prolonged cooling periods to prevent new oxidation or heat creep
Extraction Process
Withdraw filament once target temperature stabilizes
Moderate resistance expected during extraction, proportional to accumulated residue
Quality Verification
Inspect extracted filament tip for burnt/colored contaminants
Repeat until filament emerges clean from subsequent pulls
Technical Considerations
Oxidation Prevention: Rapid cooling minimizes carbonization risks
Material Compatibility: Nylon’s thermal stability enhances contaminant adhesion during extraction
Alternate Solutions: Hotend replacement remains the only comparable alternative for severe contamination cases
Maintenance Advantages
Cost Efficiency: Reduces need for nozzle replacements
Print Quality: Maintains consistent extrusion patterns
Longevity: Extends hotend component lifespan through carbon deposit removal
Implementation Notes
Temperature Calibration: Verify material-specific glass transition temperatures
Safety Protocols: Use heat-resistant gloves during extraction
Tool Preparation: Ensure filament cutters accessible for tip trimming between pulls
A brass or copper wire brush should be kept available for periodic nozzle and hotend cleaning. Before initiating prints—particularly when material buildup is visible on the heater block or nozzle—clean the components with a wire brush while heated to remove accumulated residue.
Cleaning Protocol
Tool Selection:
Nylon Brushes: Preferred for routine cleaning due to reduced abrasiveness
Metal Brushes: Use brass/copper variants over steel to minimize nozzle wear
Heating Requirement: Perform cleaning while nozzle is heated to facilitate material removal
Nylon Brush Caution: Limit contact time to brief wipes to prevent melting on hot surfaces
Operational Benefits
Print Quality: Reduces burnt material transfer to prints
Nozzle Longevity: Prevents carbonized material accumulation
Maintenance Efficiency: Addresses oxidation risks from residue buildup
Implementation Guidelines
Pre-Print Routine: Integrate cleaning into standard setup procedures
Tool Maintenance: Replace brushes showing filament contamination or wear
Safety Note: Use heat-resistant gloves during hotend interaction
Technical Rationale
Abrasion Management: Softer metals (copper/brass) preserve nozzle geometry
Thermal Dynamics: Heated material becomes pliable for effective removal
Contamination Prevention: Regular cleaning maintains optimal thermal transfer properties
You shouldn’t heat your hotend until you are ready to extrude. If you leave filament in a heated hotend for long periods of time you will increase your chance of nozzle clogs and oxidization of the material.
Make sure all of your end G-codes have the script M104 S0, which turns off your hotend after completing a print.
• Make sure you have a well-made hotend and that everything is tightened when heated to 240°C or higher. Take proper precaution to not over-tighten. • Purge old material by pushing down new material an inch and pulling out quickly. Cut off any old material that is stuck onto the filament and repeat the process until there is no longer any excess residue. • Use cleaning filament, clear nylon, or PC. If not, you can use the material you are printing with. • Cold pull by extruding cleaning filament/Nylon through the hotend at 250°C. Allow the nozzle to then cool to 140°C – 160°C, and pull the filament out. Repeat this process until you no longer get discoloring. • Don’t leave filament in a heated hotend for extended periods of time. • Use a silicone sock to reduce black spots on your print.
We recommend reading the “” page, particularly where oozing is discussed, to help prevent excess material from coming out of the nozzle.
