The humidifier hums along to the air compressor’s chugs. It’s wintertime. The birds have gone quiet, the neighbors hauled out their blow-up Santa, and guitars are coming in with cracks.

And if you’ve added a 3D printer to your shop, those seasonal shifts might be quietly ruining your prints. As we know from our guitar-work, ambient temperature isn’t just about comfort– it’s a critical variable for the materials we use.

At its core, our entire craft is physics– whether it’s the way wood resonates or the way finish reacts to seasonal shifts. Why does a bone nut sound sharper and brighter than an ebony one? Because bone is denser and harder, with fewer air pockets (pores) to soak up the vibrations. And why does lacquer check and crack during the winter? Cold makes things shrink– but not always at the same rate. Wood and lacquer contract at different speeds. When something has to give, it’s usually the hard layer of lacquer that goes first. (Though some old Yamahas I’ve seen might disagree…)

If you’re interested, over the next few months, I want to dig into the physics that underpin 3D printing. I think it’s important to have a loose grasp on what’s actually happening in our printers if we want to use it to its full potential. We’ll start with heat, and when we’ve exhausted the topic, we’ll move onto motion. From there we’ll explore materials themselves.

Today, I want to talk about some fundamental aspects of heat, as it relates to our printing.

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Heat is a critical factor that enables the 3D Printing process. It’s the energy that turns cold plastic into flowing, molten possibility. You put electricity into the machine, it turns that electricity to heat in the hot-end, and the nozzle acts as a channel for the molten plastic to flow through. From there on out, molten plastic is drawn into precise lines, solidifying as it cools– layer by layer– setting the foundation of every print. But what happens when the balance is off?

Heat doesn’t just melt the plastic– it also controls whether your print succeeds or ends up as spaghetti. To get off the ground, our prints have to stick to the build plates in our machines. Here’s where the physics comes into play: What we’re contending with is the Glass Transition Temperature. The Glass Transition Temperature (Tg) marks a critical range where a material transitions from stiff and brittle to soft and flexible. It’s not the molten state, where plastic flows freely, but the point where polymers soften into a “gummy,” pliable state.

In 3D printing, staying within the margins of this range is crucial. The plastic must reach this state to bond to the build plate and to seamlessly accept new layers on top. If you’ve ever run out of filament and resumed a print after the top layer has cooled, you can almost always see the layer where that shift occurs. This is because the top layer has cooled below the Glass Transition Temperature and instead of the two layers merging together, we’re simply sticking new molten plastic to a colder, more solid layer. The new top layer can shift or droop slightly and this creates artifacts on your print. But we’re getting carried away. Let’s get back to the Glass Transition Temperature.

If we want to relate things back to lutherie, we can think about bending guitar sides. The process isn’t exactly the same, but it’s a useful metaphor for what happens in your printer. When we bend sides, we usually soak or spray the wood and then apply heat. The water and heat soften the cellulose fibers and lignin, making the wood pliable.

In the same way that heat turns brittle sides into a pliable material for bending, it also transforms solid filament into a molten state where it can flow easily– though the specifics differ. It’s this temporary flexibility– or plasticity– that lets us bend wood and print with filaments. The gist is this: heat makes materials pliable, whether it’s wood, lacquer, or filament. In the case of 3D Printing, heat softens the filament to a molten state and the printer cools it just enough for it to stay bonded to the print bed. This allows your print to take shape, layer by layer. And for 3D Printing, the Glass Transition Temperature is at the heart of it all.

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Nothing’s worse than checking on a print and finding a pile of spaghetti on your build plate. That mess? It often starts with what happens in the Glass Transition Temperature range.

When we lay down our first layer of plastic, it’s nice and toasty from the hot-end. But not for long. Heat escapes the plastic in two directions: into the build plate and into the air. This cooling is necessary to stabilize the base for the next layer– but it’s all about balance.

You might remember this from science class: some materials conduct heat and others insulate. While the air certainly takes some of the plastic’s heat, it’s a pretty good insulator. The metal bed, on the other hand, is a terrific conductor, meaning it absorbs and loses heat far faster than air– and that’s a problem. If the bed steals too much heat from that critical first layer, adhesion fails– and your print is doomed before it’s even begun. Fans complicate things further by rapidly cooling the molten plastic. This disturbs the warm “shield” of air around the print and introduces cooler air that is ready to pull more heat away from the plastic. We’ll talk more about fans in a future essay.

Lucky for us, these problems have been solved by people way smarter than me. The solution? Heat the build plate so the bottom layer stays just on the edge of molten and stable. Maintaining the Glass Transition Temperature isn’t always essential, but that “gummy” plasticity adds grip to the system. When the bottom layer loses its “gummy” state and solidifies, the print is much more likely to come loose from the build plate. Fortunately, this isn’t the only system affecting whether your print stays in place.

There are other non-heat factors at play, too, which help us prevent some problems with excessive bed temperatures. These mechanical and material properties are why the various build plate surfaces and filaments have different recommended bed temperatures– but the deeper material science is a story for another day.

The heat in a 3D Printing system is more complex than just “hit the temperature,” though. As we’ll learn in future essays, heat loss is the primary reason that your prints underextrude and get gappy when you crank the speed up too high.

And while maintaining a heated bed is crucial for adhesion, pushing the temperature too high introduces new problems, like sagging or “Elephant’s Foot.” If you’re printing something that needs near-perfect dimensional accuracy along the Z Axis, you may run into headwinds at higher bed temperatures.

Keep in mind that bed temperature is just one of several factors affecting dimensional accuracy; others include cooling rates and material properties, which we’ll explore in future articles. But these issues remind us that precision isn’t just about solving individual problems– it’s about staying within the margins that keep the entire process stable.

A final adhesion point, unrelated to temperature. You absolutely have to keep your build plate clean. It doesn’t matter how good your settings are, if you’re trying to print on grease, it’s going to slip. The internet loves to use isopropyl alcohol or dish soap and water. I think those are a pain in the ass. I use Simple Green, diluted ~1:10 with water, but you can dilute it even further. Whatever you use, the goal is to clean off the grease from our hands, the dust from the environment, and the residue from previous prints.

When I clean my build plate, I pull it out of the machine, spray it a couple of times, wipe it with a clean rag, and put it back. Being careful not to touch the printing area– Always use the tabs!

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Heat can make or break a 3D print. Nail the balance, and you’ve laid the foundation for success. Miss it, and you’ll be scooping spaghetti off your build plate, wondering why another project landed in the “art bin.”

This is just the beginning, though. Mastering the initial layer is the first step toward a successful print. But managing heat throughout the print turns potential into reality. Next time, we’ll explore heat management , as well as the concept of equilibrium. Because in 3D printing, as in lutherie, balance is everything.