Why Is PLA Filament 1.75mm?

Kingroon Blue PLA 1kg 3D Printer Filament

The 1.75mm diameter for PLA (Polylactic Acid) filament has become a de facto standard in consumer 3D printing, particularly for Fused Deposition Modeling (FDM) printers. This seemingly arbitrary size is the result of a combination of historical, practical, and engineering factors that have shaped the 3D printing industry. In this technical blog post, we’ll explore the reasons behind the dominance of 1.75mm PLA filament, delving into its origins, technical advantages, manufacturing benefits, and why it has persisted over other diameters like 3mm.

Historical Context: The Birth of 1.75mm

The 1.75mm filament standard emerged during the early days of consumer 3D printing, particularly with the rise of the RepRap movement in the late 2000s. RepRap, an open-source project aimed at creating self-replicating 3D printers, played a pivotal role in standardizing filament sizes. Early 3D printers used a variety of filament diameters, but 1.75mm and 3mm (actually closer to 2.85mm in modern usage) became the most common.

The choice of 1.75mm was influenced by the availability of extrusion equipment and materials at the time. Industrial plastic extrusion systems, which were adapted for 3D printing, could reliably produce filament at smaller diameters like 1.75mm with consistent tolerances. As hobbyists and manufacturers began producing filament for desktop 3D printers, 1.75mm became a practical choice because it was easier to manufacture with the existing technology and offered compatibility with the Bowden and direct-drive extruders being developed.

Technical Advantages of 1.75mm Filament

The 1.75mm diameter offers several engineering and practical advantages that have cemented its place as the preferred filament size for PLA and other materials in consumer 3D printing.

1. Improved Extrusion Control

Source: https://3dpros.com/guides/fdmreference-hotend

Smaller filament diameters allow for finer control over material flow in the extruder. The volume of material extruded is proportional to the cross-sectional area of the filament, which scales with the square of the diameter. For a 1.75mm filament, the cross-sectional area is significantly smaller than that of a 3mm filament:

● Cross-sectional area of 1.75mm filament:
 The area is calculated as pi times the radius squared. For a 1.75mm diameter, the radius is 0.875mm. So, the area is approximately pi * (0.875)^2, which equals about 2.405 square millimeters.

● Cross-sectional area of 3mm filament:
 The area is calculated as pi times the radius squared. For a 3mm diameter, the radius is 1.5mm. So, the area is approximately pi * (1.5)^2, which equals about 7.069 square millimeters.

This means a 3mm filament has roughly three times the cross-sectional area of a 1.75mm filament, requiring more force and torque from the extruder motor to push the same length of filament. The smaller 1.75mm diameter allows for more precise control, especially at lower flow rates, which is critical for detailed prints with fine layer heights.

2. Compatibility with Bowden Extruders

Bowden extruders, which use a tube to guide filament from the extruder motor to the hotend, are common in many consumer 3D printers due to their lightweight print heads and reduced moving mass. The 1.75mm filament is more flexible than 3mm filament, making it easier to feed through the curved PTFE (Teflon) tubes used in Bowden systems without excessive friction or binding. This flexibility reduces wear on the extruder components and improves reliability during long prints.

3. Faster Melting and Heating

The smaller diameter of 1.75mm filament means less material needs to be heated and melted in the hotend at any given time. This reduces the thermal mass, allowing the hotend to reach the target temperature more quickly and maintain consistent heating. For PLA, which typically prints at temperatures between 190°C and 220°C, this results in faster print times and reduced energy consumption compared to 3mm filament, which requires more heat to melt its larger volume.

4. Tighter Tolerances and Consistency

Filament diameter consistency is critical for reliable 3D printing. Variations in diameter can lead to under- or over-extrusion, affecting print quality. Manufacturing 1.75mm filament with tight tolerances (typically ±0.05mm or better) is easier than for larger diameters because smaller filaments are less prone to warping or ovalization during the extrusion and cooling process. This consistency is particularly important for PLA, which is sensitive to moisture and temperature variations that can affect its diameter during manufacturing.

5. Market Momentum and Ecosystem Compatibility

Once 1.75mm filament gained traction in the early 3D printing community, it created a self-reinforcing cycle. Printer manufacturers designed their machines to use 1.75mm filament, filament producers scaled up production to meet demand, and the ecosystem of hotends, nozzles, and extruders standardized around this size. Today, the vast majority of consumer 3D printers, especially those aimed at hobbyists, are optimized for 1.75mm filament, making it the default choice for PLA and other materials like ABS, PETG, and TPU.

Manufacturing Considerations for 1.75mm Filament

Producing 1.75mm filament involves extruding molten PLA through a die, cooling it, and spooling it with precise control to maintain diameter consistency. The 1.75mm diameter is advantageous in manufacturing because it aligns with standard extrusion equipment, which can achieve high precision at smaller diameters. Smaller filaments cool more uniformly, reducing internal stresses that could cause warping or ovalization. Additionally, 1.75mm filament requires less raw material per meter than 3mm filament, lowering production costs. The smaller diameter also allows for faster spooling, increasing throughput for manufacturers. These factors make 1.75mm an economical and reliable choice for producing high-quality PLA filament, meeting the demands of the consumer 3D printing market.

Comparing 1.75mm PLA to Other Materials

While 1.75mm is the standard for PLA, it’s also widely used for other filament materials like ABS, PETG, and TPU, but PLA’s properties make it particularly well-suited for this diameter. Unlike ABS, which requires higher printing temperatures (230–250°C) and is prone to warping, PLA’s lower melting point and minimal shrinkage allow it to leverage the precision of 1.75mm filament for detailed prints. PETG, with its higher viscosity, benefits from the 1.75mm diameter’s lower extrusion force, though it may require slower print speeds. TPU, a flexible filament, takes full advantage of 1.75mm’s flexibility in Bowden systems.

Why Not 3mm or Other Sizes?

While 3mm filament (or 2.85mm, as it’s often more accurately labeled) is still used in some printers, particularly older or industrial models, it has largely been supplanted by 1.75mm in the consumer market. Here’s why:

● Increased Stiffness: 3mm filament is stiffer, which can lead to issues in Bowden systems where the filament must navigate curves. This stiffness also requires more robust extruder motors, increasing the cost and complexity of the printer.

● Higher Torque Requirements: As mentioned earlier, the larger cross-sectional area of 3mm filament demands more force to extrude, which can strain smaller stepper motors used in desktop printers.

● Slower Response Times: The larger volume of material in 3mm filament takes longer to heat and cool, which can slow down print speeds and make it harder to achieve fine details.

Other filament diameters, such as 1mm or 2mm, have been experimented with but never gained widespread adoption. Smaller diameters like 1mm are difficult to manufacture with consistent tolerances and are too flexible for reliable feeding, while intermediate sizes like 2mm offer no significant advantages over 1.75mm and disrupt the established ecosystem.

Practical Considerations for PLA Specifically

PLA, being a biodegradable thermoplastic derived from renewable resources like corn starch, has unique properties that align well with the 1.75mm standard. Its low melting point (around 150–220°C, depending on the formulation) makes it well-suited for the smaller thermal mass of 1.75mm filament, allowing for quick and efficient melting in the hotend. PLA’s relatively low viscosity when melted, compared to materials like ABS, facilitates smooth extrusion through smaller nozzles, and the 1.75mm diameter complements this by requiring less force to push through the hotend. Additionally, PLA’s minimal warping and low printing temperatures make it a favorite among hobbyists, aligning with the 1.75mm standard’s dominance in the consumer market.

Challenges and Trade-Offs

While 1.75mm filament has clear advantages, it’s not without challenges:

● Fragility: PLA filament, especially at 1.75mm, can be brittle and prone to snapping if mishandled or stored improperly. This is less of an issue with 3mm filament, which is more robust.

● Spool Compatibility: The smaller diameter means more filament length is required per unit volume, which can lead to larger spools or more frequent spool changes for large prints.

● Extruder Wear: In high-speed printing, the smaller filament diameter can cause more wear on extruder gears due to the higher rotational speed needed to feed the filament.

The Future of Filament Standards

As 3D printing technology evolves, will 1.75mm remain the standard? For now, the ecosystem is deeply entrenched, with most consumer printers, filament manufacturers, and accessory makers optimized for 1.75mm. However, advancements in extruder design, such as high-flow hotends or pellet-based printing systems, could challenge the dominance of filament-based printing altogether. In the meantime, 1.75mm remains the go-to choice for its balance of precision, compatibility, and manufacturability.