Converts rotation into reciprocating (linear back & forth) motion.

Functioning parameterized design, so you can make it as big as you want.

I designed this as a motion study, and to see how well this would work on a 3d-printer. It works surprisingly well.

It's currently designed to be hand-operated, but easily modifiable to be motor-driven. Motor-driving it is on my short-list.

In the hand-driven configuration, it needs to be held together by hand as you turn it to get the correct motion.

I would be very happy to see your application for this!

The case could use some modifications (e.g. attachment points) depending on your application.

I recommend a Frequency 3, Radius 1 inch, Height 1 inch as a working starting point.

Anything below Frequency 3 will bind. I've tried 1, 2, and 3. If you modelled in some support tracks for Freq 1 or 2, it could work.

Anything below about a 1:1 ratio (radius to amplitude) will bind at frequency 3 (I've gotten a 1:2 at frequency 1 almost working, adding extra support track may fix this if you want to try something small with longer travel)

Edit mechanism.scad to set paramters:

amplitude: size of linear motion peak-to-peak frequency: how many peaks per rotation bearing_radius: how big are your balls inner_radius: how wide should the moving part be outer_radius: how thick should the outer case be lip_radius: how wide should the 'handle' be lip_height: how tall should the 'handle' be shaft_radius: save material or make a drive-shaft slip-fit

optionally adjust these on your next print: ring_slip: slip between outer and inner rings bearing_slip: slip around balls

Export the stl files. I do this by commenting out (//) all but the part I am exporting from the --- CSG --- block at the bottom of the file. Expect the sine_toroid_race to take a very long time to render: hopefully someone adds better intersection handling or lofting to the next version of scad.

Print: 1x outer case 1x torus race 1x sine torus race Nx slide (where N=Frequency)

Assemble:

1. insert Torus Race into Outer Case, leaving the race exposed.
2. insert a Slide into every track in the Outer Case, overlap the ball hole with the Torus Race, and insert a ball into each of the slides. It's easy with 3 or fewer slides. If your frequency is >3, you may need extra fingers.
3. push the Torus Race into the Outer Case so the 2nd hole on the slide is just sticking out.
4. insert the Sine race and line the race up with the holes on the slides. Carefully insert the balls through the holes into the race.
5. push the sine race all the way in.
6. Grab the outer case in one hand, and the lip in the other. Rotate the sine race via the lip while keeping the pieces pressed together.