Hello, I'm a student in community college and don't have much CAD and mechanical engineering experience. I made a model in FreeCAD based on Dr. Thang's "Two button mechanism 2"
.
- thang two button recreation1.png (116.77 KiB) Viewed 2149 times
I made the 16mm diameter holes on the panel before adding an M16 screw with the Fasteners workbench, but I noticed the threads fit within a 16mm diameter. It could still be secured by screwing it into something behind the panel, but then there is less contact area. I suspect this could make it looser and contribute to wear if the assembly is jiggled around. To avoid this, I could have used a cut with the screw instead of a sketched hole or maybe KurtF's
Thread Maker.
- thang two button recreation2.png.png (44.56 KiB) Viewed 2149 times
I made a small gap between the inner button and leaf spring when the outer button is closed because I wanted to avoid compressive stress in the leaf spring's diagonal part as it is bent downwards by allowing it to maintain its length. If there was no gap, the diagonal part could be compressed by about 0.3mm, and it's about 1cm long, so the strain is about 0.03. From this
article by Han-Seung Ko et al., the Young's modulus of PLA is about 3.1 GPa, so the stress in the leaf spring would be about 100 MPa if it compressed as the inner button is pushed all the way in before the rightmost spring pushes them out, and this is below the tensile strength given in the article but I'm not sure whether it would experience plastic deformation. I'm not very familiar with flexural stress but maybe I could use the article's data to guess if it's within the elastic limit if I calculated it.
(Edit: the compression should have been about 0.3mm, not 0.2mm)
I used hooks to connect the inner button via the spring with large pitch to the rest of the mechanism. The design was meant to allow the spring to work in different orientations, and for one side to compress back into a hole when the other falls into a hole via gravity. I avoided screwing it into the button and spring to make it easy to manually assemble. Alternatively the outer button can be opened up more and have another half attached to it with a snap-fit (I was reminded by this
video) after the inner button and springs are connected.
- thang two button recreation5.png (39.12 KiB) Viewed 2149 times
The hook on the button is thin compared to the hook on the spring. I don't think this is important because I don't expect radial motion to be significant or the stress when the spring's hook is off-center to be significant.
- thang two button recreation6.png (58.78 KiB) Viewed 2149 times
I put sketches on the YZ plane of various parts together in one body of only sketches to make it easier to figure out the dimensions. I still ended up making ShapeBinders in separate bodies and copied the sketch via the ShapeBinders to make the various parts.
Dr. Thang has linked to STEP file(s) for his model in his video description.
Invitation for feedback, criticism, advice. Thank you.
Code: Select all
OS: Ubuntu 20.04.3 LTS (XFCE/xfce)
Word size of FreeCAD: 64-bit
Version: 0.20.28936 (Git) AppImage
Build type: Release
Branch: (HEAD detached at 7b18e86)
Hash: 7b18e86bac28aa5103c50bed101eebdbd39f9659
Python 3.9.13, Qt 5.12.9, Coin 4.0.0, OCC 7.5.3
Locale: English/United States (en_US)
Installed mods:
* fcgear 1.0.0
* fasteners 0.3.43
