This is a reworked update of Things 614962 and 652717.
The geometry has been corrected to give a more truly linear output, and some fixing points have been enlarged for greater robustness.
A complete set of stl file have been uploaded here.
The model is based on mechanism 329 from 507movements.com.
Designed in Moi and made in PLA on an Ultimaker 1.
An animation created in Blender is available here: https://youtu.be/T4Nh_J__8oU
A video of the printed model is available here: https://youtu.be/Cy_rkiBq3vw
Note the flexing!
Please check orientation prior to printing.
I used PLA and recommend it over ABS for this application.
I recommend 1.2mm walls and 40% fill.
For the larger prints I used a brim.
I used support for one item only - the smaller gear. This was a disadvantage of the improved geometry. In the earlier version I cheated a bit on the geometry to make the gear easier to print but when I (recently) created an animation of the older version I was a bit shocked by how much adverse effect the cheat had on the linearity of the output. Hence the redesign.
Generally I design holes in which something rotates to a nominal dimension such as 6mm diameter or 8mm diameter and the male parts about 0.3mm of 0.4mm under nominal.
Post printing I use hand reamers to bring the holes to the correct size and roundness.