How Does 3D Printing Work? From Digital Model to Finished Print

A 3D printer builds the cross-sections of a digital model one after another until they form a solid object. Picture a shallow tray for the screws you take out while fixing something. Near the bottom, a horizontal slice through the tray is a filled rectangle. Above the floor, the same slice looks like a rectangular ring. Stack those shapes in order and you get a tray with an open top.

Software called a slicer works out those layers for the 3D printer. How the machine forms each layer depends on the process. A filament printer draws lines of softened plastic. An LCD resin printer uses a pattern of light to harden the shape of a layer.

1. Start with the shape you want to print

You can design the tray in CAD, download an existing design, or use a 3D scan as a starting point. For a simple rectangular tray, drawing it to the dimensions you want is usually easier than scanning a real one. What matters is that the file describes a three-dimensional shape, including the recess that holds the screws.

Open the model in a slicer compatible with your printer. Check the dimensions before you go further. If a tray meant to be palm-sized looks as small as a postage stamp on the virtual build plate, correct its scale now. Rotate the model, too. From above, a solid block and an open tray can have the same outline. Looking inside makes it easier to spot a missing recess.

2. Slice the model and preview a few layers

Choose the profile for your printer and material, then place the model on the virtual build plate. For this filament example, set the tray flat with the opening facing up. Slice it and move through the preview one layer at a time. At the bottom you should see paths covering the floor. Farther up you should see just the walls. If the preview fills the recess all the way to the rim, check the model before starting the print.

The model describes the object. The sliced file describes how a particular machine will make it. An STL can describe the tray’s surface, for example. A filament slicer commonly outputs G-code with motion and extrusion instructions. A resin printer may use a file containing layer images and exposure settings instead. ELEGOO’s Mars 4 is one example that supports the GOO format. When you switch machines, go back to the model and slice it with the right profile.

3. Prepare the printer and material

On a filament machine, the spool feeds the extruder, which drives the filament toward the heated nozzle. Check that the selected material matches the spool and that the build plate is seated and prepared according to the printer’s instructions. A stable first layer gives the walls above it a base to build on. If the first lines pull loose, use the printer calibration guide before committing to the whole tray.

For LCD resin printing, the machine uses a vat of liquid photopolymer and a build plate. Choose a compatible resin and its recommended profile. Set up the handling and cleanup area before opening the bottle, following the resin’s safety data sheet and the machine manual.

4. Watch how a layer takes shape

On a filament printer, follow the nozzle

An FDM 3D printer pushes heated plastic through a nozzle in narrow beads. For a floor layer of our tray, the nozzle traces the perimeter and lays adjacent lines across the base. Each new bead bonds to the material beside or beneath it as it cools. Once the floor is complete, the nozzle follows the narrower wall paths and leaves the middle open. The machine changes the height between the nozzle and the part for the next layer.

On an LCD resin printer, follow the light

An LCD 3D printer forms a layer by exposing selected areas of liquid resin at the same time. On a typical bottom-up machine, the build plate starts close to the transparent vat film, leaving a thin gap for resin. A light source sits beneath the vat. The LCD acts as a mask, allowing light through in the pattern specified for that layer. Resin in the exposed areas hardens, attaching to the build plate on the first exposure and to the growing print on later ones. The cured layer separates from the vat film, fresh resin flows into the gap, and the next exposure begins.

The tray still needs a floor, walls, and an empty recess. What changes is how it should be oriented and supported for the machine you’re using. An FDM file laid flat for filament printing won’t tell a resin printer where to expose a layer or how to support the part.

What about powder printers?

On a polymer SLS system, a fresh layer of powder is spread across the bed and a laser fuses the selected cross-section. Loose powder around the part supports it during the build. That’s a third way to make a layer from a digital shape. For materials and examples of where each process fits, see our introduction to 3D printing.

5. Remove the print and check the result

For the filament tray, let the plate and part cool as directed, then remove the tray using the procedure for that build surface. Take off any temporary supports. Put the tray on a flat surface, check whether the corners rock, and try it in the space you designed it for. Those checks tell you more about the next revision than the print-complete message does.

A resin print usually comes off the machine with uncured resin on its surface. Follow the resin maker’s cleaning, drying, and post-curing directions, including the specified wash medium and cure settings. Support-removal timing also depends on the material and geometry. For a visual example, ELEGOO’s first resin print tutorial moves into part processing at about 3:25.

Questions that come up when you see a print in progress

Why can I see lines on a curved surface?

A curve gets approximated by a series of thin steps. Those steps are easiest to see where a surface slopes gently. A smaller layer height can reduce that staircase effect, but it adds layers to the job. Check your slicer’s preview and time estimate for the part and profile you plan to use.

What’s the difference between infill and supports?

In a filament print, infill is a pattern inside the part, between its outer walls. It stays there after printing. Supports hold up features while they’re being made and are generally removed afterward. The empty space for screws in our tray is part of the design. Increasing infill changes the material inside the tray’s solid sections, not the space where the screws go.

How long will it take to print?

For the filament tray, start with the estimate after slicing it with your printer and material profile. A tray that is 15 mm tall at a uniform 0.2 mm layer height has 75 layers. The solid floor and the open wall layers contain different amounts of printing, so the slicer calculates time from the paths and speeds in each layer. Increasing the tray’s width, adding supports, or changing the profile can change the total even when the layer count stays the same.

For an LCD resin example, suppose the sliced model, including its supports, is 30 mm tall at a 0.05 mm layer height. That makes 600 layers. If a complete layer cycle averages 10 seconds, including exposure, separation, and pauses, the layer cycles total about 100 minutes (1 hour 40 minutes). This is a worked estimate using an assumed cycle time. Use your machine’s actual settings and allow for longer bottom-layer cycles. Several models that fit on the plate at the same height can share each layer’s exposure, so doubling their number may add little printing time. Budget separately for setup, washing, drying, and curing.