Nested gimbal rings are a nice print-in-place test: every ring has to turn freely, and nothing may fuse. This post builds four rings and a globe in Python with manifold3d, and shows the three mistakes that fused my first attempts.
1. A ring is a revolved rectangle
from manifold3d import Manifold as Mf, CrossSection as CS w, t = 4.4, 4.0 # radial width, thickness def ring(R): return Mf.revolve(CS.square([w, t], True).translate([R, 0]), 96) revolve spins the profile around Z, so the ring lies in the XY plane. Rotate it with .rotate([90,0,0]) and so on to get the other planes. Each pair of neighbours shares one axis: Z, then Y, then X, then Z for the globe.
2. Cone pin and cone socket
The child ring grows a cone pin on its outer surface. The parent gets a matching cone socket, offset by the clearance CL = 0.45. A cone self-centres, and it prints without supports when the tip points sideways or up.
def cone(r1, r2, h, pos, d): # d = unit direction return Mf.cylinder(h, r1, r2, 32).transform(rotm(d)).translate(list(pos)) g = inner_parent - outer_child # gap between the rings L = g + 1.5 # pin reaches 1.5 mm into the parent wall pin = cone(2.7, 1.1, L, d * outer_child, d) slope = (1.1 - 2.7) / L sock = cone(2.7 + slope*(g-1.2) + CL, 2.7 + slope*(L+0.7) + CL, L+0.7-(g-1.2), d * (outer_child + g - 1.2), d) parent = parent - sock 3. The three mistakes
- The socket must start before the wall. A ring wall is curved. A socket that starts exactly at the nominal inner radius leaves a thin skin at the edges of the cone, and the pin fuses to it. Start the socket 1.2 mm earlier.
- Check every pair with
a ^ b. After the final union,decompose()tells you the count of parts. When it is too low, intersect each pair and print the volume. A volume above 0.01 names the fused pair. - Keep the stand away from sockets. My pedestal column reached into the lowest socket and filled it. Stop the column at the outer surface of the ring.
I have not test printed this yet. The meshes are separate manifold solids with 0.45 mm radial clearance.
