Sometimes you just need someone to hand you the next bolt. In OpenSCAD.
This library accepts a bolt kind (e.g. "M3") a length you need to cover (e.g., 36.5 mm), and returns the previous-sized, next-sized bolt lengths, and how deep to respectively, countersink or add clearance.
This allows you to keep your bolt lengths real-life-sized, without driving the design from the bolt size.
Anyway, check this out:
use <next-bolt/next-bolt.scad>;
echo(next_bolt("M3", 36.5));
// Echoes:
// [
// ["next", [["length_clearance", 3.5], ["length", 40]]],
// ["previous", [["length", 35], ["countersink", 1.5]]]
// ]
So for the aforementioned bolt and length, our choices are to either use a M3x40 bolt, and add 3.5 mm of bolt-sized clearance past the thing we're trying to reach with our bolt, or use a M3x35 bolt and countersink it by 1.5 mm.
examples/simple.scad demonstrates a this conundrum, with a nutcatch thrown in:
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(The examples use catchnhole for convenience, but this library is absolutely
agnostic about how you choose to (or not to!) render your bolts. You do you.)
Add a git submodule to your project:
git submodule add https://github.com/mmalecki/openscad-next-bolt next-boltuse <next-bolt/next-bolt.scad>;
echo(next_bolt("M3", 36.5));