parametric_brackets/parametric_bracket.scad

// parametric extrusion brackets
// Scott Alfter
// 20 July 2018

// settings

nominal_extrusion_width=20; 
screw_diameter=5;
gap=0.4; // adjust for a snug fit
thickness=2.8; 

// uncomment one of the following to render

corner_bracket();
//t_bracket();
//double_t_bracket();
//alignment_sleeve(140, "Bot"); // for Hypercube 300 assembly
//alignment_sleeve(155, "Top"); // for Hypercube 300 assembly
//alignment_sleeve(60, ""); // for test fit

// other constants needed later

tw=(nominal_extrusion_width+gap+2*thickness); // total width
iw=(nominal_extrusion_width+gap+thickness)/2; // dimension from center of cube to center of hole
sleeve_gap=gap+.2; // looser fit for alignment sleeves

// top-level modules

module corner_bracket()
{
	corner();
	translate([0,tw,0])
		tube();
	translate([tw,0,0])
	rotate([0,0,90])
		tube();
	translate([0,0,tw])
	rotate([90,0,0])
		tube();
	translate([tw,0,tw])
		brace();
	translate([0,tw,tw])
	rotate([0,0,90])
		brace();
	translate([tw,tw,0])
	rotate([-90,0,0])
		brace();
}

module t_bracket()
{
	t();
	translate([0,0,tw])
	rotate([90,0,0])
		tube();
	translate([0,0,-tw])
	rotate([90,0,0])
		tube();
	translate([tw,0,0])
	rotate([0,0,90])
		tube();
	translate([tw,0,tw])
		brace();
	translate([tw,0,-tw])
	rotate([180,0,0])
		brace();
}

module double_t_bracket()
{
	dt();
	translate([0,0,tw])
	rotate([90,0,0])
		tube();
	translate([0,0,-tw])
	rotate([90,0,0])
		tube();
	translate([tw,0,0])
	rotate([0,0,90])
		tube();
	translate([0,tw,0])
		tube();
	translate([tw,0,tw])
		brace();
	translate([tw,0,-tw])
	rotate([180,0,0])
		brace();
	translate([0,tw,tw])
	rotate([0,0,90])
		brace();
	translate([0,tw,-tw])
	rotate([180,0,90])
		brace();
	translate([tw,tw,0])
	rotate([-90,0,0])
		brace();
}

module alignment_sleeves()
{
	alignment_sleeve(140, "Bot");
	translate([1.5*tw,0,0])
		alignment_sleeve(155, "Top");
}

// lower-level modules

module alignment_sleeve(length, label)
{
	// frame tools:
	// 140 mm (center-to-center) between corner and T
	// 155 mm (center-to-floor) under double-T

	linear_extrude(length-tw-nominal_extrusion_width)
	difference()
	{
		square(nominal_extrusion_width+2*sleeve_gap+2*thickness, true);
		square(nominal_extrusion_width+2*sleeve_gap, true);
	}
	translate([0,-iw-thickness/2,10])
	rotate([90,0,0])
	linear_extrude(1)
		text(label, halign="center", valign="center", size=nominal_extrusion_width/2);
}

module brace() // a pair of braces
{
	d=tw/2-4;
	translate([0,-d,0])
		brace_sub();
	translate([0,d,0])
		brace_sub();
}

module tube() // four panels to make a tube
{
	translate([0,0,-iw])
		panel();
	translate([0,0,iw])
		panel();
	translate([-iw,0,0])
	rotate([0,90,0])
		panel();
	translate([iw,0,0])
	rotate([0,90,0])
		panel();
}

module corner() // three panels and three edges in a corner
{
	translate([0,iw,iw])
		edge();
	translate([iw,0,iw])
	rotate([0,0,90])
		edge();
	translate([iw,iw,0])
	rotate([0,90,0])
		edge();
	translate([0,0,-iw])
		panel();
	translate([0,-iw,0])
	rotate([90,0,0])
		panel();
	translate([-iw,0,0])
	rotate([0,90,0])
		panel();
}

module t() // three panels and two edges in a T
{
	translate([iw,0,iw])
	rotate([0,0,90])
		edge();
	translate([iw,0,-iw])
	rotate([0,0,90])
		edge();
	translate([0,-iw,0])
	rotate([90,0,0])
		panel();
	translate([0,iw,0])
	rotate([90,0,0])
		panel();
	translate([-iw,0,0])
	rotate([0,90,0])
		panel();
}

module dt() // two panels and four edges in a double-T
{
	translate([0,iw,iw])
		edge();
	translate([0,iw,-iw])
		edge();
	translate([iw,0,iw])
	rotate([0,0,90])
		edge();
	translate([iw,0,-iw])
	rotate([0,0,90])
		edge();
	translate([0,-iw,0])
	rotate([90,0,0])
		panel();
	translate([-iw,0,0])
	rotate([0,90,0])
		panel();
}

// basic components

module panel() // basic unit: a square plate with a hole, centered on the origin
{
	d=tw/2;
	translate([0,0,-thickness/2])
	linear_extrude(thickness, convexity=10)
	difference()
	{
		polygon([[-d,-d],[-d,d],[d,d],[d,-d]]);
		circle(d=screw_diameter+gap, $fn=45);
	}
}

module edge() // a stick to fill in the corners where panels meet
{
	d1=tw/2;
	d2=thickness/2;
	translate([0,0,-d2])
	linear_extrude(thickness, convexity=10)
		polygon([[-d1,-d2],[d1,-d2],[d1,d2],[-d1,d2]]);
}

module brace_sub() // a diagonal brace
{
	d=tw/2;
	translate([0,thickness/2,0])
	rotate([90,0,0])
	linear_extrude(thickness, convexity=10)
	polygon([[-d,-d],[d-3,-d],[-d,d-3]]);
}