A test object for "self-tapping" triangular holes in printed parts. Print the STL then fill out the Google form.

Readme.md

I've switched to using slightly triangular holes in my printed parts, because they "self tap" quite nicely using machine screws (the points of the triangles provide enough space that the swarf doesn't jam the thread). My hope is that this extends the tolerance on hole size, meaning I don't have to worry quite so much about getting diameters exactly right. This means the print should work first-time on a greater range of printers. If you could print the test piece below (trylinder_selftap_holes_test.stl) and then fill out the form that would be really helpful.

The easiest way to get the test piece is to right click the raw download link and choose "save link as..." to save to an STL file - gists don't give the files the correct mimetype, so otherwise your browser will just render the STL as text, which isn't so helpful...

trylinder_selftap_holes_test.scad

/* Test object for self-tapping holes
Released under CERN open hardware license v1
*/

use <utilities.scad>;

sizes = [2.4, 2.6, 2.8, 2.9, 3.0, 3.1, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4];
N = len(sizes);
r = 5;

difference(){
    hull(){
        cylinder(d=2*r, h=6);
        translate([2*r*(N-1),0,0]) cylinder(d=2*r, h=6);
    }
    
    for(i=[0:N-1]) translate([2*r*i,0,0]){
        trylinder_selftap(sizes[i], h=999, center=true);
        
        translate([0, -r+0.5, 0.5]) rotate([90,0,0]) linear_extrude(1) text(str(sizes[i]), size=4, halign="center");
    }
}

trylinder_selftap_holes_test.stl

I left a long comment about the numbers on the sides on the GOSH forum about the test piece. It may be of interest to those trying to understand them. ( https://forum.openhardware.science/t/printed-hole-test-object/1712/7 )