linkmail-scad

An OpenSCAD library for print-in-place sheets of interlocking links, like chainmail. The sheet prints flat in one piece, and each link comes off the bed linked to its neighbours but free to move.

Usage

use <src/linkmail.scad>

square_mail(link_loop_rad = 3.5, link_circle_rad = 1, loop_skew = 45, cut_offset = 1,
            n = 3, m = 3, clearance = 0.4);

square_mail(link_loop_rad, link_circle_rad, loop_skew, cut_offset, n, m, clearance = 0.4)

An n by m sheet of square links.

Argument	Meaning
link_loop_rad	Radius of each loop, in mm. A link reaches twice this from its centre.
link_circle_rad	Radius of the round wire the loops are made of, in mm.
loop_skew	How far each loop tilts out of the flat, in degrees. Neighbouring loops tilt opposite ways and pass through each other.
cut_offset	How much to cut off the top and bottom of each link so it sits flat on the bed, in mm. Must be less than 2 * link_circle_rad, or the cut severs the loops.
clearance	The smallest gap between two neighbouring links, in mm.

The links are placed as close together as clearance allows. If no spacing leaves that much room, the render stops and says how much room there can be. At a 45° skew with a 1 mm wire, a 3 mm loop radius leaves at most about 0.33 mm, and a 3.5 mm loop radius about 0.71 mm.

square_mail_spacing(link_loop_rad, link_circle_rad, loop_skew, cut_offset, clearance) returns that spacing, for placing a sheet or sizing its border. It is in src/square_link.scad: use that file too to call it.

square_link(link_loop_rad, link_circle_rad, loop_skew, cut_offset, fn = 16)

A single link: four tilted loops around a hub, cut flat top and bottom.

Triangle links

triangle_link() in src/triangle_link.scad makes a three-loop link, and tri_hex_link(link_circle_rad, link_loop_rad, link_spacing = 0.5) places six copies of its child in a ring. There is no triangle sheet yet, and the ring is spaced by the older link_spacing factor, not by a clearance, so its gaps are unchecked.

Examples

• examples/square_link_example.scad: one square link.
• examples/square_linkmail_example.scad: a 3 by 3 sheet.
• examples/triangle_link_example.scad: a triangle link and a ring of six.

How the spacing is found

square_link_gap() measures the smallest distance between the surfaces of two square links a given distance apart: between the loops of one and the loops of the other, and between the loops of one and the hub of the other. Diagonal neighbours are not measured: for loop radii of 3 to 6 mm and skews of 30° to 60°, they were at least 2.3 mm further apart than side neighbours at the chosen spacing. The gap rises and then falls as the links move apart, and the spacing is the closest one at which it reaches clearance.

The rendered loops are polygons that sit inside the true round surfaces, so the printed gap is a little larger than clearance: in the 3 by 3 example at 0.4 mm, the smallest gap in the exported mesh is 0.46 mm.

Development

With just, OpenSCAD and Python 3, just test runs the geometry checks in tests/test_linkmail.scad, renders every example with warnings as errors, checks that a cut too deep for the wire is refused, and counts the links in the example sheet to make sure none fused. just images renders the pictures in assets/.

License

MIT. See LICENSE.