5 Ways to Disable Z Probe Nozzle Heating Before Homing in Marlin

Understanding Z Probe Trigger Temperatures and Potential Issues

When your 3D printer homes, the Z-probe, the component responsible for determining the print bed’s height, needs to be in tip-top shape to get an accurate reading. One factor that can significantly influence the accuracy of your Z-probe, especially if you’re using a probe that relies on physical contact like a BLTouch or inductive probe, is the temperature of the nozzle. Think of it this way: materials expand and contract with temperature changes. If your nozzle is hot from a previous print or preheating, it will expand slightly. This seemingly minor expansion can throw off your Z-height calibration, leading to a first layer that’s too close or too far from the bed. If it’s too close, you might end up with a squished, uneven first layer or even damage your print surface. Conversely, a first layer that’s too far from the bed won’t adhere properly, potentially causing the print to fail.

Different materials react to temperature changes differently. For example, a brass nozzle will expand more than a hardened steel nozzle at the same temperature. Knowing the coefficient of thermal expansion for your specific nozzle material can help you predict how much it will expand at different temperatures. However, it’s generally more practical to simply control and account for the temperature rather than calculating the precise expansion.

Overwriting the Z-probe’s default nozzle heating behavior gives you greater control over this process. Instead of letting the printer decide when and how to heat the nozzle before homing, you can dictate a specific temperature, or even disable nozzle heating entirely during homing. This is particularly useful when you’re working with a material that requires a significantly different printing temperature than your previous print. Imagine switching from printing PLA at 200°C to PETG at 240°C. If the nozzle is still hot from the PLA print, the Z-probe might register an inaccurate height, leading to a messy first layer with the PETG. By overwriting the default behavior and ensuring the nozzle is at a consistent temperature (or cold) before homing, you create a reliable and repeatable starting point for your prints.

Here’s a breakdown of potential scenarios and how controlling nozzle temperature can help:

By understanding how nozzle temperature affects your Z-probe and using the overwrite function, you can significantly improve the accuracy and reliability of your 3D prints. In the following sections, we’ll delve into how to actually implement this overwrite function on popular firmware like Marlin and Klipper.

Adding the M104 Command to Preheat the Nozzle

Preheating your nozzle before the Z-probe homes can be a real game-changer, especially when printing with materials that require a specific temperature range for accurate probing. Often, the default startup routine of 3D printers involves homing all axes *before* the nozzle reaches its target temperature. This can be problematic, particularly with materials like PETG or ABS, which can ooze or stick to the bed at lower temperatures, potentially interfering with a precise Z-offset. Introducing an M104 command into your start G-code allows you to preheat the nozzle to a suitable temperature *before* homing, mitigating these issues.

How it Works

The M104 command is a standard G-code instruction used to set the target temperature for the extruder hotend. By incorporating this command into the start G-code, which is executed at the beginning of every print, we can ensure the nozzle begins heating up *prior* to any homing or probing procedures. This allows the nozzle to reach a more stable temperature before the Z-probe interacts with the print surface, resulting in a more consistent and accurate first layer.

Implementation: A Step-by-Step Guide

Adding the M104 command to your start G-code is a straightforward process, generally accessible through your printer’s firmware settings. Here’s a more detailed breakdown:

1. Locate your start G-code: Access your printer’s firmware settings, usually via a connected computer or the printer’s control panel. Look for a section labeled “Start G-code,” “Startup G-code,” or something similar. This section contains the G-code commands that are automatically executed at the beginning of every print.
2. Insert the M104 command: Within the start G-code section, add the following command: M104 S[Temperature]. Replace [Temperature] with the desired preheating temperature for your material. For instance, for PLA, you might use M104 S200 (for 200°C). Ideally, place this command *before* any G28 command (which typically initiates homing). This ensures preheating begins immediately.
3. Adjust the wait time (optional but recommended): While the M104 command sets the target temperature, it doesn’t inherently pause the G-code execution until that temperature is reached. To ensure the nozzle has sufficient time to reach the target temperature, consider adding an M190 command after the M104. The M190 command waits for the bed to reach the set temperature and can also be used for the nozzle by using S parameter. Example M190 S[temperature]
4. Save the changes: After inserting the M104 and M190 command (if used), save the changes to your start G-code. The exact procedure for saving depends on your printer’s firmware but usually involves clicking a “Save” or “Apply” button.

Here’s a practical example of how this might look within your start G-code:

By implementing this simple modification, you can improve the accuracy and consistency of your Z-probe offset and enhance the quality of your first layer, particularly when working with temperature-sensitive materials.

Ensuring Safe Homing with a Heated Nozzle

Homing, the process where your 3D printer establishes its zero position, is crucial for accurate prints. However, a cold nozzle can sometimes snag on the print bed during this process, potentially causing damage. Pre-heating the nozzle before homing mitigates this risk, ensuring a smoother and safer start to your printing process. Let’s explore how to implement this precaution.

Overriding Z Probe Nozzle Heating Before Homing

Many 3D printers, especially those using Marlin firmware, have a setting that dictates whether the nozzle needs to reach a certain temperature before homing. However, this setting can sometimes be counterproductive, especially if you’re dealing with a previously heated nozzle. Overriding this setting allows you to initiate homing immediately, saving time and energy, especially beneficial when using materials like PLA where the nozzle might already be sufficiently warm.

Methods for Overriding Pre-Homing Nozzle Heating

There are several ways to bypass the pre-heating requirement before homing, depending on your printer’s setup and firmware:

Detailed Explanation of Start G-code Modification

Modifying your start G-code is often the most convenient method. Within your slicer software (e.g., Cura, PrusaSlicer), locate the “Start G-code” settings. Here, you’ll add a command that sets your desired nozzle temperature. For instance, adding M104 S50 will set the nozzle to 50°C. Crucially, the M104 command doesn’t wait for the nozzle to reach that temperature before proceeding to the next command. This allows you to immediately initiate homing with the G28 command following your temperature setting. So, your updated start G-code would look something like: M104 S50 ;Set nozzle to 50C \\n G28 ; Home all axes. The semicolon introduces a comment, enhancing readability.

If you *do* want to wait for the nozzle to reach a certain temperature before homing (for example, if you are printing with a material that needs a higher starting temperature), you can use the M109 command instead. For instance, M109 S190 will set the nozzle to 190°C and wait until it reaches that temperature before executing the following G-code (like the G28 homing command).

This modified start G-code will be executed at the very beginning of every print using that profile, ensuring a consistently warmed nozzle before homing. Remember to save your slicer profile after making these changes.

Testing the Modified Homing Sequence

After implementing changes to your 3D printer’s firmware to enable nozzle heating before the Z-probe homes, thorough testing is crucial. This ensures the modification works as intended and doesn’t introduce unintended consequences. A systematic approach to testing will help identify any potential issues early on.

Initial Visual Inspection

Before powering on your printer, conduct a visual check. Ensure all wiring related to the nozzle heater and thermistor remains secure and correctly connected. Double-check that no wires are pinched or stressed due to your modifications. Look for any signs of damage or loose components around the hotend and mainboard.

Dry Run without Heating

For the first test, disable the nozzle heating command in your modified homing sequence. This allows you to observe the homing movements without the added variable of temperature. Power on your printer and initiate the homing sequence. Observe the Z-probe’s deployment and movement. Verify that it travels to its intended location without obstruction and triggers the Z-endstop correctly. This step isolates potential mechanical issues unrelated to the heating element.

Low-Temperature Heating Test

Now, enable the nozzle heating command in your start G-code or homing sequence. Set a conservative target temperature, around 50°C for PLA or 80°C for PETG. This minimizes the risk of damage if something goes wrong. Initiate the homing sequence again and monitor the nozzle’s temperature readout. Ensure it reaches the target temperature before the Z-probe begins its homing movements. Observe the entire homing process, verifying proper Z-probe deployment and triggering.

Target Temperature Heating Test

Once the low-temperature test passes, increase the target temperature to your usual printing temperature for your chosen filament. For instance, 200°C for PLA or 230°C for PETG. Repeat the homing sequence and monitor the nozzle temperature. Confirm that the nozzle reaches the target temperature before homing commences, and that the entire sequence completes without error. Observe the Z-probe’s accuracy after heating to ensure thermal expansion hasn’t introduced any offset.

Repeated Homing Cycles

To ensure consistency, perform multiple consecutive homing cycles at your target printing temperature. This helps verify that the modified homing sequence functions reliably over multiple iterations and identifies any intermittent issues. Pay close attention to the nozzle’s temperature and the Z-probe’s behavior during each cycle. Look for any variations in homing position or inconsistencies in temperature regulation.

Testing with Filament Loaded

After confirming successful repeated homing cycles, load your chosen filament. Initiate the homing sequence again and observe the entire process. Ensure the filament doesn’t interfere with the Z-probe’s movement and that the nozzle reaches the target temperature as expected before homing begins. This verifies that the presence of filament doesn’t negatively impact the modified homing sequence.

Edge Case Scenarios

It’s important to test edge cases to ensure robustness. Simulate a power outage during the heating phase by turning off your printer mid-cycle. Restart the printer and observe its behavior. A well-designed system should handle such interruptions gracefully and either resume the heating process or safely abort the homing sequence. Also, test scenarios where the thermistor provides incorrect readings. While unlikely, this could lead to overheating. A well-configured firmware should include thermal runaway protection to prevent damage in such situations.

Observed Results During Testing

Keeping a record of observations during testing can be immensely helpful. This allows you to track the behavior of your modified homing sequence and identify patterns if issues arise. Below is a sample table to demonstrate how you might organize your observations.

Overwriting Z-Probe Nozzle Heating Before Homing

Overwriting the default behavior of heating the nozzle before a Z-probe homing cycle can be beneficial in certain 3D printing scenarios. For instance, when using a probe that isn’t sensitive to temperature fluctuations or when working with materials that require a cold environment during initial setup. This modification minimizes the risk of oozing or material degradation before the print starts, especially with temperature-sensitive filaments. However, it’s crucial to understand the implications and ensure the chosen Z-probe functions reliably at ambient temperature.

The specific method for overriding this behavior depends on the firmware used in your 3D printer. For Marlin firmware, this typically involves modifying the START\_PRINT macro in the Configuration.h file. Comment out or remove the line responsible for heating the nozzle. Similarly, in Klipper firmware, you can adjust the start\_print macro within your printer’s configuration file. A detailed understanding of your firmware and its configuration is necessary before making any changes.

It’s crucial to test the Z-probe’s accuracy after implementing this change. Perform several test homing cycles to confirm consistent and reliable probing results. If inaccuracies arise, revert the changes or explore alternative solutions like implementing a dedicated probe heating cycle prior to homing.

People Also Ask About Overwriting Z-Probe Nozzle Heating Before Homing

Why would I want to prevent nozzle heating before homing?

Several situations benefit from preventing nozzle heating before the Z-probe homes. One primary reason is to avoid filament oozing or material degradation, particularly when using temperature-sensitive materials. Additionally, some probe types may not require a heated nozzle for accurate measurements, making pre-heating redundant.

What are the potential drawbacks?

The main drawback is the possibility of inaccurate Z-probing if the probe’s accuracy is temperature-dependent. Ambient temperature fluctuations can affect some probes. Also, certain filaments may adhere poorly to the bed at lower temperatures, impacting first-layer adhesion if printing immediately after homing.

How do I restore the default behavior?

Restoring the default behavior involves reversing the changes made to the firmware configuration. In Marlin, uncomment or re-add the nozzle heating line within the START\_PRINT macro in Configuration.h. For Klipper, revert the start\_print macro to its original state in your printer’s configuration file. Remember to save and upload the modified configuration to your printer.

Are there alternative solutions?

Instead of completely disabling nozzle heating before homing, consider implementing a dedicated probe heating cycle. This approach involves heating the nozzle only to a temperature sufficient for accurate probing, then cooling it down before the actual print begins. This offers a compromise between ensuring probe accuracy and minimizing the risk of oozing or material degradation.