3D printing and slicers

Example 1 Estimating mass and filament length

The CAD camera mount has a volume of 4.2 cm³ and a surface area of 30 cm², printed with 2 perimeters, 0.45 mm line width, 20% infill and 1.75 mm PLA of density 1.24 g/cm³ (Prusament PLA datasheet). This is a simple estimate; the slicer computes it more accurately.

import math

V_CM3, AREA_CM2 = 4.2, 30.0
PERIMETERS, LINE_W_MM, INFILL = 2, 0.45, 0.20
RHO, D_MM = 1.24, 1.75                                  # g/cm³, mm

shell = min(V_CM3, AREA_CM2 * PERIMETERS * LINE_W_MM / 10)
material = shell + INFILL * (V_CM3 - shell)
mass = RHO * material
cm_per_gram = 1 / (RHO * math.pi * (D_MM / 20) ** 2)
print(f"shell {shell:.2f} cm³ + infill {INFILL:.0%} of core -> {material:.2f} cm³")
print(f"mass {mass:.2f} g, filament {mass * cm_per_gram / 100:.2f} m ({cm_per_gram:.1f} cm per gram)")
for inf in (0.1, 0.4, 1.0):
    print(f"infill {inf:.0%}: mass {RHO * (shell + inf * (V_CM3 - shell)):.2f} g")

shell 2.70 cm³ + infill 20% of core -> 3.00 cm³
mass 3.72 g, filament 1.25 m (33.5 cm per gram)
infill 10%: mass 3.53 g
infill 40%: mass 4.09 g
infill 100%: mass 5.21 g

In a small part like this most of the material is in the walls, so raising infill from 20% to 40% adds only about 10% mass; adding perimeters usually buys strength more efficiently.

Example 2 Flat or upright

A 50 × 20 × 2 mm mounting plate with 0.2 mm layers, an average flow of 8 mm³/s and 1.5 s per layer change (hypothetical values).

SIZE = (50.0, 20.0, 2.0)                 # mm
LAYER, FLOW, CHANGE_S = 0.2, 8.0, 1.5     # mm, mm³/s, s per layer
volume = SIZE[0] * SIZE[1] * SIZE[2]

for name, height in (("flat", SIZE[2]), ("on edge", SIZE[1]), ("upright", SIZE[0])):
    layers = round(height / LAYER)
    minutes = (volume / FLOW + layers * CHANGE_S) / 60
    print(f"{name:<8}: {layers:>3} layers, about {minutes:4.1f} min")

flat    :  10 layers, about  4.4 min
on edge : 100 layers, about  6.7 min
upright : 250 layers, about 10.4 min

Printing upright takes about two and a half times as long as flat, because there are more layers. A tall thin part also wobbles during printing, and if the plate is bent in use, the layer bonds sit in the weak direction. Flat is better for both time and strength for this part.