Reuleaux Triangle Mechanism Kit Card

Overview

Reuleaux triangles are a really interesting geometric shape and now you can watch how they work with this miniature kit!  What makes them so cool is that they are polygon-based shapes with constant width but a moving centroid.  Those properties allow it to take rotational motion around a fixed axis and generate reciprocating motion, which is what you'll see in this mechanism kit.

I made the design in OnShape and and it is comprised of the following parts:

• 1x Base
• 2x End Supports
• 2x Forks
• 2x Reuleaux Triangles
• 2x Bottom Axle Pieces
• 1x Top Axle Handle
• 1x Top Axle Support
• 4x Discs

Update on 7/16/23: Edited tolerances on some parts and made sacrificial supports on forks easier to remove.

Printing

I printed the kit card in Burnt Titanium PLA on the Prusa i3 MK3.  No supports necessary!  I've included the original STL, g-code, and source file.

If you re-slice, just be sure to orient the parts similar to the g-code examples.  I also recommend slowing down your print speed, especially for perimeters, so that the print comes out clean.

Assembling

I recommend having a small file, some super glue, and sand paper handy for assembly.

1. Break the parts out of the kit and clean off the excess sprues. Recommend using a small detail file.
2. The forks have sacrificial supports that run along the inside perimeter.  Use needle-nose pliers to carefully remove the thin strips of plastic so that fork looks like a u-shaped u-beam.
3. Assemble the bottom axle by sliding the two symmetric pieces together.  If parts are loose, use a little super glue to firmly connect them.
4. Assemble the top axle by sliding the handle axle and support axle pieces together.  If parts are loose, use a little super glue to firmly connect them.
5. For the next steps, note that the axles have raised sections along their length for help aligning the triangles, forks, and discs.
6. Slide one of the discs onto the bottom axle until it overlaps with one of the raised sections.  If the disc is loose, use a little super glue to fix it. 
7. Slide a fork onto the bottom axle until it aligns with the disc (note that the fork should be a little loose - do not glue!!).
8. Slide a second disc onto the bottom axle and sandwich the fork between the two discs, approximately aligned with the middle of one of the raised sections on the axle.
9. Repeat Steps 6-8 for the remaining discs and fork.  Glue as needed, except for the forks.
10. Slide the two Reuleaux triangles onto the top axle, from the end that does not have the handle.  Align each triangle with the two raised sections, starting with the one that is closest to the handle.
11. Slide the small disc onto the top axle and align it approximately with the raised section that is furthest from the handle.
12. Lay out the top and bottom axles so that the triangles align with the forks and can slide into the slot on the forks.  Adjust fork and triangle positioning as necessary.
13. Attach the end supports to either side of the axles.  Note that the handle on the top axle will have to be inserted into the hole on the end support first.
14. Once everything is aligned, with the axles parallel to each other and the end supports parallel to each other, carefully press the posts on the bottom of the end supports into the slots on the base.
15. Give it a test and realign as needed.  If the triangles are moving a little stiff, you can try sanding their edges and/or applying some lubricant

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