3d scanning and printing

Assignment for this week

design and 3D print an object (small, few cm) that could not be made subtractively
3D scan an object (and optionally print it)
Link to this week’s home work page

This page is organized as follows:

Designing a 3d object
3d printing
3d scanning

Designing a 3d object

After a quick look on the internet, I decided to 3dprint a C60 molecule which is known to be difficult to obtain by injection molding techniques. The position of the atoms in a C60 molecule and the bonds between atoms (which atom is linked to which) are easily available on the web. I used this source. The datafile contains 9 columns (C, #, x, y, z, 1, # 1st neighbor, # 2nd neighbor, # 3rd neighbor). I wrote a simple script in R to create an openSCAD command file that would draw the atom as spheres and the bonds as cylinders. The code is given below:


data = read.table("~/Desktop/c60.cart3d", skip=1)

# x,y,z position of the spheres
x = data[,3]
y = data[,4]
z = data[,5]

# bonds (x2 - x1, y2 - y1, z2 - z1) = (hx, hy, hz)
# cylinder, height = sqrt(hx^2+hy^2+hz^2)
# the cylinder is along z by default
# we must rotate it along x,y,z
# in a spherical coordinate system
# 		hx = h*sin(theta)*cos(phi)
#		hy = h*sin(theta)*sin(phi)
#		hz = h*cos(theta)
# where theta is the angle of rotation along x and phi is the angle of rotation along z
# --> theta = acos(hz/h) and tan(phi) = hy/hx --> phi = atan(hy/hx)
#
text = "R=0.5; F=10;\nunion()\n{\n";
# atoms
for (i in 1:60){
	text = paste(text, "translate([",x[i],",",y[i],",",z[i],"]) sphere(r=R, $fn=F);\n", sep="");
}

# bonds (used centered cylinders, translate, rotate)
for(i in 1:60){
		i1 = data[i, 7];
		hx = x[i1]-x[i]; hy= y[i1]-y[i]; hz = z[i1]-z[i];
		h = sqrt(hx^2+hy^2+hz^2);
		tx = (x[i1]+x[i])/2; ty=(y[i1]+y[i])/2; tz = (z[i1]+z[i])/2;
		theta = acos(hz/h);
		phi = atan(hy/hx);
		text = 	paste(text, "translate([",tx,",",ty,",",tz,"]) rotate([-acos(",hz/h,"),0,-atan2(",hx,",",hy,")]) cylinder(r=0.2, h=",h,", center=true, $fn=F);\n", sep="");
		i2 = data[i, 8];
		hx = x[i2]-x[i]; hy= y[i2]-y[i]; hz = z[i2]-z[i];
		h = sqrt(hx^2+hy^2+hz^2);
		tx = (x[i2]+x[i])/2; ty=(y[i2]+y[i])/2; tz = (z[i2]+z[i])/2;
		theta = acos(hz/h);
		phi = atan(hy/hx);
		text = 	paste(text, "translate([",tx,",",ty,",",tz,"]) rotate([-acos(",hz/h,"),0,-atan2(",hx,",",hy,")]) cylinder(r=0.2, h=",h,", center=true, $fn=F);\n", sep="");
		i3 = data[i, 9];
		hx = x[i3]-x[i]; hy= y[i3]-y[i]; hz = z[i3]-z[i];
		h = sqrt(hx^2+hy^2+hz^2);
		tx = (x[i3]+x[i])/2; ty=(y[i3]+y[i])/2; tz = (z[i3]+z[i])/2;
		theta = acos(hz/h);
		phi = atan(hy/hx);
		text = 	paste(text, "translate([",tx,",",ty,",",tz,"]) rotate([-acos(",hz/h,"),0,-atan2(",hx,",",hy,")]) cylinder(r=0.2, h=",h,", center=true, $fn=F);\n", sep="");
}
text = paste(text, "}\n")

writeLines(text, con="~/Desktop/C60.scad", useBytes=F)

The openSCAD command file is just a succession of commands that create spheres after a proper translation of x, y and z and cylinders (bonds) that need to be translated and rotated.

The resulting STL exported file can be viewed below (with a low res to avoid big sizes).

You can find the stl file here.

3d printing

I used a UPmini for my 3d printing. The stl file can be imported into the 3d printer sofware.

The object can be rescaled. Here I had to rescale everything by a factor 5. Some printing parameters can be tuned by the user: z thickness (here 0.25 mm), fill density, etc.

Finally, once the user clicks on print and validates the print window that lists some parameters (0.25 mm thickness, loose filling, ABS filaments), a new window with the estimated weight of the 3d printed object (here 8.8g) and the duration of the printing process (here 57 min) appears.