3D printing is easy. You can buy a 3D printer off the shelf for a few hundred of your Earth pounds, download patterns from thingiverse and be printing solid stuff straight away. Creating your own 3D models is harder, and it seems to me that this is now the bottleneck (at least, if you don’t want to spend a lot of money). There are several options. You can scan a real item, if you have a 3D scanner, and then use really awkward tools to manipulate the mesh. You can persuade powerful and confusing tools for animation and modelling like Blender to create models. You can use infuriatingly limited free versions of commercial tools like Sketchup. Or if you have really deep pockets, you can buy a proper CAD system.

I don’t like any of the above. I’m a programmer, and have a mechanical engineering background. I want to create precise, preferably parametric, models of components which I can then print out and fit together with other components to make machines. Up till now, I’ve been using OpenSCAD, and it’s been pretty good. OpenSCAD allows you to define shapes precisely using numbers, and combine them exactly (wrong word, I know) to create useful things. I love it. But it’s always had one major flaw (and a few little ones, but that’s another story). Building a model in OpenSCAD is like writing a program: it supports functions and loops, but it doesn’t support variables. At least not variable variables. You can assign a value to a variable and use it later, but that value cannot change. This is a bit of a pain, and it limits what you can do. Now there is an alternative, and that makes me happy.

The new kid on the block

OpenJSCAD is an entirely browser-based (yes, you read that right) editor and renderer for 3D models. It uses a language quite similar to OpenSCAD (indeed, it can import OpenSCAD files), but more powerful and a bit like C. And it supports proper variables. Hurrah! Here’s a screenshot of a little something I knocked up in it:

Try doing that in OpenSCAD. I did, and the spiral ramp was not easy. Here’s an assembly of a few of them, printed out and stacked together. A ball bearing runs around them very nicely:

Try OpenJSCAD. If you don’t like it, I’ll give you your money back.

Here’s my .jscad file which created the ball chute. You can simply cut the text and paste it into OpenJSCAD if you want to try it.

// title: Spiral ball bearing chute
// author: Peter Robinson
// license: None.  Free for all.
// description: A stackable spiral chute for ball bearings.

var radius = 50;
var slotwidth=6;
var wallthickness=1;


function main(params) {

    var a=2;
    return union(
        section(),
        section().translate([0,0,20]).rotateZ(90),
        section().translate([0,0,40]).rotateZ(180),
        section().translate([0,0,60]).rotateZ(270)
        );

}

function section(){
    return union(
        ramp(1,11,radius-4,radius-4,4),
        ramp(6,11,radius-3,radius-3,1),
        ramp(1,11,radius+3,radius+3,6),
        hub()
        );

}

function hub(){
    return  difference(
        union(
            CSG.cylinder({
            start:[0,0,0],
            end:[0,0,10],
            radius: 10,
            resolution:36
            }),
            CSG.cylinder({
            start:[0,0,10],
            end:[0,0,15],
            radiusStart: 8,
            radiusEnd: 7,
            resolution:36
            }),
            spoke().rotateZ(-27.5),
            spoke().rotateZ(-27.5-45).scale([1,1,0.5])
        ),
        union(
            CSG.cylinder({
            start:[0,0,-1],
            end:[0,0,17],
            radius: 6,
            resolution:36
            }),
            CSG.cylinder({
            start:[0,0,-0.5],
            end:[0,0,5.5],
            radiusStart: 7.9,
            radiusEnd: 6.9,
            resolution:36
            })
        )

    );
}

function spoke(){
    return CSG.cube()
        .scale([radius/2-slotwidth/2,1,5])
        .translate([-radius/2,0,5]);
}

function spiral(){
    var hex = CSG.Polygon.createFromPoints([
            [0,slotwidth/2, 0],
            [0,-slotwidth/2, 0],
            [0,-slotwidth/2, radius],
            [0,slotwidth/2, radius]
    ]).setColor(
        [0, 0.8, 0]
    );
    var angle = 5;
    return hex.solidFromSlices({
        numslices: 365 / angle,
        callback: function(t, slice) {
            var coef = 1 - t * 0.8;
            return this.
            translate([0 , radius, t*10]).
            rotateZ(angle * slice);
        }
    });

}

function ramp(slotwidth,climb,innerradius_start,innerradius_end,basethickness){
    var hex = CSG.Polygon.createFromPoints([
            [0,0, 0],
            [0,slotwidth, 0],
            [0,slotwidth, 1],
            [0,0, 1]
    ]).setColor(
        [0, 0.8, 0]
    );

    var base = CSG.Polygon.createFromPoints([
            [0,0, 0],
            [0,slotwidth, 0],
            [0,slotwidth, 1],
            [0,0, 1]
    ]).setColor(
        [0, 0.8, 0]
    );
    var angle = 5;
    var radiuschange = innerradius_end-innerradius_start

    var bottom = base.solidFromSlices({
        numslices: 95 / angle,
        callback: function(t, slice) {
            return this.
            translate([0 , innerradius_start +t*radiuschange, 0]).
            scale([1,1,basethickness]).
            rotateZ(angle * slice);
        }
    });

    var spiral = 
        hex.solidFromSlices({
        numslices: 95 / angle,
        callback: function(t, slice) {
            return this.
            translate([0 , innerradius_start +t*radiuschange, 0]).
            scale([1,1,climb*(0.1+t*0.9)]).
            rotateZ(angle * slice);
        }
    });


    return union(
        bottom,
        spiral.translate([0,0,basethickness])
    );

}