Our Larval Engineer asked for help with an OpenSCAD model of a 3D printable claw that, she says, has *nothing at all* to do with the upcoming Night of Little Horrors. Not having had an excuse to fiddle with the new (and lightly documented) `sweep()`

functions, I gnawed on the `sweep-drop.scad`

example until this popped out:

That might be too aggressively sloped up near the top, but it’s a start.

The OpenSCAD source code:

use <sweep.scad> use <scad-utils/transformations.scad> function shape() = [[0,-25],[0,25],[100,0]]; function path(t) = [100*(1+sin(-90-t*90)), 0, (100 * t)]; step = 0.01; path_transforms = [for (t=[0:step:1-step]) translation(path(t)) * scaling([0.5*(1-t) + 0.1,0.75*(1-t) + 0.1,1])]; sweep(shape(), path_transforms);

It’s perfectly manifold and slices just as you’d expect; you could affix it to a mounting bracket easily enough.

Some notes on what’s going on…

The `t`

index determines all the other values as a function of the layer from the base at `t=0`

to the top at `t=0.99`

.

The `shape()`

defines the overall triangular blade cross-section at the base; change the points / size to make it look like you want.

The `path()`

defines the XYZ translation of each slab that’s extruded from the shape() cross-section. I *think* the Z value sets the offset & thickness of each slab. The constant 100 in the X value interacts with the overall size of the `shape()`

. The 90 values inside the `sin()`

function set the phase & scale `t`

so the claw bends the right way; that took some fiddling.

The parameters in `scaling()`

determine how the `shape()`

shrinks along the path() as a function of the `t`

parameter. The 0.1 Finagle Constants prevent the claw from tapering to a non-printable point at the tip. I *think* the Z value must be 1.000 to avoid weird non-manifold issues: the slabs must remain whatever thickness the sweep functions set them to be.

It compiles & renders almost instantly: much faster than I expected from the demos.

The folks who can (and do!) figure that kind of model (and the libraries behind it) from first principles have my undying admiration!

## Blowback