Is PETG Backwards for Motor Mounts?

Grams decide whether a printed airplane flies or just sits on the bench looking like one.. every wall, every bit of infill and every extra perimeter gets paid for by the motor and the battery, so the filament choice matters before the first slice even starts. PLA is the easy default, but ABS and ASA are lighter in the spool, and hybrid ABS/ASA spools are being printed into whole airframes.

Why ABS and ASA Come Out Lighter

Density is grams per cubic centimetre (g/cm³) of the solid plastic. Bambu Lab's data sheets list PLA Basic at 1.24 and PETG Basic at 1.25, while their ASA sits at 1.05. Print the same shape at the same settings and the ASA part comes out roughly 15 percent lighter than PLA (1.05 against 1.24) and 16 percent lighter than PETG. A hybrid ABS/ASA spool advertised at 1.07 works out to about 14 percent.

A figure of 15 to 20 percent lighter gets quoted, and density alone only reaches the bottom of that range. The rest has to come from settings, because the plastic is the same in the part whatever the slicer does with it. Densities also differ from maker to maker- published ASA sheets run from 1.05 up past 1.1- so the sheet that came with your spool beats any table.

Toughness is the other half of the pitch. Bambu's own comparison puts ASA at 41.0 kJ/m² impact strength in the XY direction and ABS at 39.3, against 34.8 for polycarbonate. Across the layers it is a different story: the same table shows ASA at 4.9 kJ/m² in the Z direction and ABS at 7.4, so layer adhesion is the weak axis in both.

Slicer Settings for a Printed Plane

The numbers below are the ones reported for a hybrid ABS/ASA spool in Bambu Studio, starting from the Generic ABS filament profile. Everything not listed stays at the default.

Filament profile      Generic ABS
Nozzle temperature    280 °C   (spool says 250 °C max)
Bed temperature       70 °C    (65 °C also works)
Wall loops            1
Top shell layers      3        (4 also works)
Sparse infill         3%       (4% adds weight)
Infill pattern        Gyroid   (adaptive cubic is the usual alternative)
Outer wall width      0.45 - 0.46 mm   (never above 0.5 mm)

Two of those sit outside what the vendor tables say, so check them against your own spool. Bambu's filament table lists ABS and ASA at 240 to 280 °C (give or take ten), so 280 is the very top of that range. It is also the temperature reported to give better layer adhesion than the 250 on the label. The bed is the bigger gap: Bambu's table lists 90 to 100 °C for ABS and ASA, while 70 is the figure reported for this hybrid. A hot plate coming off a job like this deserves a little care, and the Scrape It, Torch It, Clip It, Seal It post has the plate-handling side of it.

One wall loop is the setting RC builders pass around, and the reason is weight: builders report that a second wall can nearly double it on a thin-skinned plane. Three or four top layers close the skin over the infill. At three percent infill the interior is mostly air anyway, so gyroid costs a little weight for extra strength while adaptive cubic is the usual alternative.

Line width works the same way: widening the outer wall line stiffens the part and adds grams, so it stays under 0.5 mm.

Slicing is free, so use it: slice, read the estimated weight, change one setting, slice again. Different infill patterns give different totals, and the slicer reports each one before any plastic is spent.

Bambu also warns that ABS and ASA warp on large models and on high infill, and asks for an enclosed printer with a properly glued plate. Low infill and a single wall happen to stay on the safe side of that warning.

Motor Mounts and the PETG Question

One piece of advice going around is to print motor mounts and servo covers in a heat-resistant material and to reach for PETG, on the idea that ABS/ASA softens around 50 °C, but the vendor numbers say otherwise.

At 0.45 MPa Bambu lists ABS at 87 °C and ASA at 100 °C, while PETG Basic comes in at 69 °C and PLA Basic at 57 °C. On paper that makes ABS or ASA the better choice beside a warm motor. The 50 °C figure is contradicted by both the ABS and the ASA data. A hybrid spool could behave differently from either, so its own sheet decides. None of the data sheets says how hot a motor mount gets, so a cheap probe thermometer on the first flights answers that.

Smell, Fumes and Drying

Bambu's product pages say these filaments can release styrene at printing temperatures, which can cause dizziness or nausea, and they recommend a well-ventilated area or an air filtration or exhaust system. Add more ventilation, or pause the print, when someone with asthma, a pregnant person or a child is around. Bambu's drying table also lists ABS and ASA at 80 °C for eight hours before printing.

Test Footage

Which filament and wall count are you flying, and what did the last crash do to it? Drop it in the comments, and a weight figure from your own slicer is welcome too.

Glossary

• ABS — acrylonitrile butadiene styrene, a tough, heat-tolerant plastic that smells while printing
• ASA — acrylonitrile styrene acrylate, a close cousin of ABS
• Density — mass per volume of the solid plastic, in grams per cubic centimetre
• Heat deflection temperature (HDT) — the temperature at which a test bar bends by a set amount under a set load, a standard measure of heat resistance
• Wall loops — the number of outline lines printed around each layer
• Infill — the pattern printed inside the walls, given as a percentage of solid
• Gyroid — a wavy infill pattern that is strong for its weight
• Slicer — software that turns a 3D model into printer instructions
• Styrene — a chemical released when ABS and ASA melt

Sources

• Bambu Lab PLA Basic data sheet — density 1.24 g/cm³, HDT at 0.45 MPa 57 °C
• Bambu Lab PETG Basic data sheet — density 1.25 g/cm³, HDT at 0.45 MPa 69 °C
• Bambu Lab ASA data sheet — density 1.05 g/cm³, HDT 92 °C at 1.8 MPa and 100 °C at 0.45 MPa
• Bambu Lab ASA product page — ASA, ABS and PC comparison table, ventilation and styrene notice
• Bambu Lab ABS product page — HDT 87 °C, styrene and ventilation notice, warping tips
• Bambu Lab filament guide table — nozzle, bed and drying settings for ABS and ASA
• BEST Filament for 3D Printed RC Planes? ABS/ASA Strength Test + Full Slicer Settings Guide — hybrid ABS/ASA test flights, slicer settings and motor mount advice
• Scrape It, Torch It, Clip It, Seal It — handling hot plates and removing ASA and PETG prints