How to Use STL Print Files in 3D Printers?

The most common file format you will encounter when stepping into the world of 3D printing is the STL (Stereolithography) format. Whether you download a complex figurine or a functional spare part, 3D modeling data is stored in this format.

However, you cannot send an STL file you downloaded via stlindir.com directly to your 3D printer. The file must first be converted into layer instructions that your printer can understand. Moreover, this process varies significantly depending on the 3D printing technology (FDM or SLA) you use.

 

Let's look step-by-step at how to prepare STL files for printing on FDM and SLA printers.

Using STL Files on FDM 3D Printers (Filament-Based)

FDM (Fused Deposition Modeling) printers print by melting plastic filament (PLA, ABS, PETG, etc.) from a spool and depositing it layer by layer through a nozzle.

The steps you need to follow when preparing an STL file for FDM technology are as follows:

1. Import the STL File into Slicer Software

Open the STL file you downloaded in one of the popular slicer software for FDM:

  • UltiMaker Cura

  • PrusaSlicer

  • OrcaSlicer / Bambu Studio

2. Positioning and Scaling

Place the model on the build plate in a way that requires the least amount of support. Having the surface of the model that contacts the build plate be as wide and flat as possible improves bed adhesion.

3. Infill and Wall Thickness Settings

The biggest advantage of FDM printers is that you don't have to print the inside of objects 100% solid.

  • Ornamental and Decorative Objects: An infill density of 10% - 15% is sufficient.

  • Mechanical / Durable Parts: An infill density of 30% - 50% and increasing the number of walls (Wall Loops) is recommended.

  • Infill Pattern: You can choose Grid, Gyroid, or Cubic patterns.

4. Support Structures

You need to add supports for angles hanging in the air against gravity (usually slopes greater than 45 degrees). Instead of standard block supports, the recently popular Tree Supports both save filament and are easily removed after printing.

5. Exporting G-code

After completing all settings, click the "Slice" button. The software converts the STL file into the printer's movement codes and creates a .gcode file. You can transfer this file to your printer via SD card, USB drive, or Wi-Fi network and start the print.

Using STL Files on SLA / Resin 3D Printers (Resin-Based)

SLA (Stereolithography) or MSLA/LCD printers cure liquid resin layer by layer using a UV light source. They are ideal for achieving fine details and smooth surfaces.

The STL preparation process in SLA technology is quite different from FDM:

1. Selecting SLA Slicer Software

Common slicer software used for SLA printers:

  • Chitubox

  • Lychee Slicer

  • Anycubic Workshop

2. Angled Positioning (30° - 45° Rule)

Never place the model flat on the build plate as in FDM with SLA printers. Flat surfaces stick to the FEP film at the bottom of the resin vat, creating a high suction cup effect, which can lead to print failure. Tilting the model at a 30 to 45 degree angle is the healthiest method.

3. Hollowing and Drainage Holes

SLA prints are printed 100% solid by default. To save resin and reduce the weight of the model:

  • Hollow the model with the "Hollow" option (set wall thickness to 2 mm - 3 mm).

  • Be sure to open Drain Holes on the bottom parts facing the resin vat. Otherwise, uncured liquid resin trapped inside may eventually burst the model.

4. Adding Supports and Using a Raft

SLA supports are much thinner than FDM but are more numerous.

  • After generating automatic supports, add manual supports to critical points.

  • Don't forget to add a Raft (Platform) to the base so the print adheres firmly to the plate.

5. Exporting in Printer Format and Post-Processing

SLA printers do not use .gcode. Depending on the brand, you export in custom sliced formats such as .ctb, .pwmb, or .goo.

Remember: After the SLA print is finished, the model must be washed with isopropyl alcohol (IPA) and undergo additional UV curing.

Differences in STL Preparation Between FDM and SLA

Feature FDM (Filament) SLA (Resin)
Slicer Software Cura, PrusaSlicer, OrcaSlicer Chitubox, Lychee Slicer
Output File Format .gcode .ctb, .pwmb, .goo etc.
Internal Structure Logic Grid/Gyroid infill (10%-20%) Hollowing + Drainage hole
Model Angle Flat surface should sit flush on the plate Should be tilted at 30° - 45°
Post-Processing Removing supports is sufficient Secondary Wash (IPA) + UV Curing

Summary

STL files you download via stlindir.com provide great results on both types of printers. The important thing is to apply the slicing logic suitable for the technology you are using:

  • If using FDM: Focus on bed adhesion, infill percentage, and correct temperature settings.

  • If using SLA: Pay attention to angled positioning, hollowing, and drainage holes.