$fn=33;

M3HoleDiam=3.4;

height=40;
thickness=3;
length=30;

// cambelt has 6mm width
innerspace=8;

render() difference() {
    frame();
    holes();
}

module frame() {
    cube([innerspace + 2 * thickness,thickness,height]);
    translate([0, thickness, 0]) cube([thickness, length, height]);
    translate([innerspace + thickness, thickness, 0]) cube([thickness, length, height]);
    
    
}

module holes(){
    // two inner holes
    translate([innerspace / 2 + thickness, 0, height / 4]) M3Hole();
    translate([innerspace / 2 + thickness, 0, height / 4 * 3]) M3Hole();
    
    translate([0, length / 4 *3, height / 2]) SideM3Hole();
    
    translate([innerspace + thickness, length / 4 * 3, height / 2]) SideM3Hole();
}

module M3Hole() {
    rotate([0,90,90])cylinder(h=thickness, d=M3HoleDiam);
}

module SideM3Hole() {
    rotate([0,90,0])cylinder(h=thickness, d=M3HoleDiam);
}