Don’t Let the Bed Cool Down on Me

Balancing Heat Before Your Print Says Goodbye

Picture this: Your printer just nailed the first layer, smooth as Kenny G. You can see the finished print becoming reality. But halfway through, you notice it: the corners are lifting, and that flawless start is slipping away… again.

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Why do corners lift after a perfect first layer? The answer lies in equilibrium– how heat moves through your print as it cools, trying to balance temperatures across the part.

It’s easy to think of print temperatures as static numbers. After all, we set them and expect them to stay steady. But in reality, they’re always in flux. Balancing heat isn’t just a technical challenge– it’s the secret dance behind every successful print.

Uneven Cooling and Thermal Stress

A print is constantly cooling. Heat naturally flows from the warmer top layers to the cooler bottom ones, while the build plate reheats the bottom layer. Fans add to this by introducing a steady supply of cooler air, amplifying the uneven cooling. 

But uneven cooling isn’t just about external factors. The print’s internal structure– particularly infill– also has a big impact on how heat moves through the part.

Infill replaces solid plastic with a mesh or pattern to save material. These air pockets act as insulators, slowing heat transfer through the part. But less material also means lower thermal mass, so infill cools faster than solid parts. This rapid cooling exaggerates thermal stresses, making corners more likely to warp and lift on complex prints.

As plastic cools, it shrinks slightly– but not uniformly. The warmer base shrinks slower than the cooler layers above, creating internal stresses that tug at the edges of your print. These uneven forces accumulate at the corners, where contraction is greatest. When the stress becomes too much, adhesion to the bed gives way, and the corners start to lift.

While internal factors like infill drive uneven cooling, they interact with external conditions– the environment surrounding your printer– which play an equally critical role in achieving equilibrium.

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The Environment

Uneven cooling becomes even more pronounced in colder shops, where the difference between the printer’s heat and the surrounding air creates sharp temperature gradients– rapid changes in temperature over short distances. When the fans bring this cool air into the printer, this temperature difference can cause inconsistent stress on your print. And that leads to warping.

This is where enclosed printers shine: by trapping air around the part, they stabilize the print environment and reduce thermal stress.

Don’t go crazy, though. Too much trapped heat can cause issues like nozzle clogs or drooping lines. Adjusting airflow using your printer’s door and top-glass can help. If you open the door slightly, it adds airflow from the shop. Closing them off helps insulate prints from colder ambient air. 

Remember that physics works on every scale. In the same way an enclosed printer stabilizes the immediate environment around a print, a warm workshop creates a protective bubble around the printer itself. If the shop is too cold, it draws heat away from the machine, making equilibrium harder to maintain.

If your workshop feels like a meat freezer, your printer’s heat isn’t stabilizing your print– it’s warming the room. Without prep, you’re not just battling the cold– you’re fighting physics. And guess who’s going to win.

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Lutherie Example

I’m going to stretch my metaphor again, but let’s compare it to humidity in wood. Think about how guitar necks respond to changing seasons. In winter, lower humidity pulls moisture from the wood, causing it to shrink and move into forward bow (the edges lift). It’s not the lack of humidity itself– it’s the change in humidity.

The same principle applies to prints: temperature shifts tug at their structure until the edges warp. Guitars need stable humidity to maintain their form, just as prints need consistent temperatures to avoid stress and deformation.

The lesson? Whether it’s wood or plastic, finding equilibrium between external forces helps reduce the stresses that distort your material over time.

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So how do we help our printer find equilibrium? 

It starts with managing the environment. Before printing, we need to account for the room temperature and ensure the machine has warmed up. 

A warm room helps your printer achieve equilibrium. In a cold shop, heat flows from the warm bed into the colder frame, making it harder to maintain the bottom layer’s Glass Transition Temperature. Preheating counters this effect, ensuring the printer’s components reach stable temperatures before printing begins.

Practically speaking, it means this: In cold environments, you’ll probably want to make sure your printer fully heats up. You can do this in a few ways. The first is to preheat your machine for 10 or 15 minutes. Preheating the bed is a safe and simple way to warm up your printer.

For extra heat, you can preheat the hot-end to around 150°C. Just make sure there’s no filament engaged to prevent clogs. If you’re using an AMS, this isn’t really an issue, since the AMS motors will pull the filament out at the end of each print. But if you’re directly feeding, you’ll want to unload the filament and pull it back.

We do this to avoid a phenomenon called heat creep. Heat creep occurs when heat travels beyond the intended melting zone, softening the filament too soon. This creates jams or clogs, as the extruder struggles to push semi-melted filament through the nozzle. By unloading the filament during preheating, you prevent this issue while letting the printer components stabilize. Many current-generation printers will automatically shut off idle hot-ends for safety and heat-creep reasons.

Another trick is to insulate your printer by draping a moving blanket over your printer. This method works well for warming up your machine quickly but is generally not recommended during printing. Some people will use one with high-temperature materials like ASA, but it’s risky for PLA or PETG, as excessive heat can cause nozzle clogs. Unless your shop is exceptionally cold, it’s best to avoid this method during active printing.

By understanding and managing heat equilibrium, you can reduce warping, improve adhesion, and work your way towards more reliable prints. With preheating, a warm workspace, and proper airflow, you’re not just battling physics– you’re working with it.

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Quick Tips for Preheating in Cold Shops

• Preheat the Bed: Warm up your printer’s base early to soak heat into the machine.
• Insulate the Printer: Close your printer’s doors to trap heat during preheating.
• Change the Environment: Try to keep the room, itself, from losing heat.

By taking a few minutes to preheat your printer, you’re not just warming it up– you’re creating the conditions for a stable, successful print.

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Equilibrium isn’t just about preheating– it’s about managing all the factors that influence heat loss and retention throughout the print. Fans are the next piece of the puzzle, actively shaping airflow and controlling how heat stabilizes.

In the next essay, we’ll dive into the art of managing fan settings and airflow to refine this balance and tackle the challenges of your specific environment or print.