Designing the lemon

The lemon shape

In geometry, a lemon is a geometric shape that is constructed as the surface of revolution of a circular arc of angle less than half of a full circle rotated about an axis passing through the endpoints of the lens (or arc).
— Wikipedia¹

I chose this shape because it suits image analysis for detecting faulty patterns and rolls smoothly on a roller conveyor.

Dimensions

The lemon measures 39 mm tall by 29 mm wide-relatively compact. I modeled it in Blender from a UV Sphere (18 segments, 9 rings), scaled 1.3 units on the Z-axis, then imported it into Autodesk Fusion to verify dimensions and create documentation.

Distinguishing the lemons

I’m printing with black PETG filament and will paint the models white afterward (currently I don’t have other filament color).

Healthy lemons will be fully white, damaged or spoiled ones will feature a clear mark, such as a cross.

Quantity

I plan to produce six sets of damaged/spoiled lemons and five sets of healthy ones.

3D Printing

I slice the STL file using Ultimaker Cura software:

• Download STL file
• Download sliced GCODE file

As a non-professional 3D printer, I’m still experimenting with settings, but here are the key ones for this print:

[general]
version = 4
name = lemon shape
definition = anycubic_i3_mega

[metadata]
type = quality_changes
quality_type = normal
intent_category = default
position = 0
setting_version = 25

[values]
acceleration_print = 1000
cool_fan_full_layer = 2
cool_fan_speed = 40
fill_outline_gaps = False
infill_before_walls = False
infill_pattern = gyroid
infill_sparse_density = 10
material_final_print_temperature = 220.0
material_initial_print_temperature = 220.0
material_print_temperature = 240.0
min_bead_width = 0.3
min_wall_line_width = 0.3
optimize_wall_printing_order = True
retract_at_layer_change = True
retraction_amount = 2.5
retraction_hop = 0.2
retraction_hop_enabled = False
skin_monotonic = True
skirt_brim_speed = =speed_layer_0
skirt_height = 1
small_hole_max_size = 3.0
speed_print = 40
speed_topbottom = 40
speed_travel = 150
speed_travel_layer_0 = 150
support_angle = 45.0
support_infill_rate = 10

Preview

The print should take about 6-7 hours and use 80g of filament (26.25 meters).

Notes

I’ll start printing soon and follow up with another post on the next steps, including painting and polishing the lemons.