This is the last of the projects in this series demonstrating top down design of assemblies using master sketches and Assembly4. This is a model of a two-speed hand drill reverse engineered from a restoration on YouTube: https://www.youtube.com/watch?v=VoiEuyAFLHM
A few comments about the modelling process which is similar to the previous projects follow in the captions of the images below:
A few concluding remarks regarding top down design and in-context modelling:
1. An assembly master sketch(es) is essential to capture design intent and to control interface locations during the design process.
2. My mantra is "keep the master simple but not too simple". Only experience will tell you how simple.
3. Sketcher carbon copies ensure linkage to the master sketch and dramatically improve sketch productivity.
4. Assembly4 facilitates the top down design process with a simple approach using local coordinate systems as "connectors" to insure 6-degree solver function.
5. Nearly any assembly constraint solver for mechanical motion can be created using Assembly4 expressions and variables. I am not a fan of too much automation that buries this function in the assembly software selectable only by myriad of tool buttons.
6. Robust modelling strategies are necessary especially for top-down design since the model will go through many changes during the design process. Avoid model breakage by attaching sketches and individual body local coordinate systems only to master sketches or origin planes.
7. I no longer use the master sketch for controlling any mechanical motion due to weaknesses in the sketcher solver for any changes over a wide range. It is more reliable to apply motion constraint solvers via expressions for the LCS's or body link attachment offset properties.
The model files from any of the projects are available to anyone for review or critique by PM request. The bevel gear template is also available by request. The files are too large to attach.
If you want to learn top down design find a restoration video of a mechanical device that interests you and give it a go. All the information you need can be gleaned from the video with a bit of effort. Using this approach rather than working from drawings is better IMO because it will force you to develop robust models that can withstand many changes as the design evolves.
OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.22261 (Git)
Build type: Release
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United States (en_US)