Does this look like your objective?

I've left the axle solid, as there were no dimensions in the post for the axle hole diameter.

idler.jpg

In an earlier post, you ask about which scanner to buy. If you mean a 3D scanner aimed at 3D printing, you'd be spending hundreds of dollars for something that could accomplish this.

One option to consider is to use photogrammetry. There are some free sites, although I've not experienced them. One takes a series of photographs from all angles and the software creates a 3D model. The file generated typically has plenty of background "litter" and often leaves holes in the model. Those holes require repair in modeling software with which one should have a strong background. The results of this process and other scanning methods are not particularly well suited for dimensionally critical parts. The scanning systems that can manage those parts will cost thousands of dollars.

Code:
$fn = 90; // smoother surface of cylinders
axle_diameter = 2;
disk_thick = 1;
disk_diameter = 10;
short_stem_height = 2;
long_stem_height = 5;
stem_diameter = 2;
addabit = 0.0625; // provide overlap to avoid z-fighting

module assembly(){
    cylinder(h = disk_thick, d = disk_diameter); // main disk
    translate([0, 0, -short_stem_height + addabit]) // move short stem below disk
    cylinder(h = short_stem_height + addabit, d = stem_diameter); // short stem
    translate([0, 0, disk_thick - addabit]) // move long stem above disk
    cylinder(h = long_stem_height + addabit, d = stem_diameter);
}
assembly();