Detent escapement model 3d printed

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jackfreecad
Posts: 53
Joined: Sun Oct 25, 2020 4:56 pm

Detent escapement model 3d printed

Post by jackfreecad »

detent.png
detent.png (133.75 KiB) Viewed 808 times
I designed, 3D printed and built this working model. It has a diameter of 170 mm
While it is mostly 3d printed in PLA, with a 0.4 nozzle, all the hardware, screws, shafts and springs are in steel ( Piano Wire), the main spring is out of a chain saw pull start
Check out the working model here:
https://youtu.be/PsLbLa05fKg
Files (23Mb) can be downloaded at this link:
(Edited link, be patient, it will take a little time to download)
https://drive.google.com/uc?export=down ... XTjQaHj--f
It is inspired by the spring detent escapement invented by Thomas Earnshaw in 1780
This escapement was mainly used in in marine chronometers
Learn more here: https://en.wikipedia.org/wiki/Thomas_Earnshaw

Made with

Code: Select all

OS: macOS 10.16
Word size of FreeCAD: 64-bit
Version: 0.21.0.32532 (Git)
Build type: Release
Branch: master
Hash: 20e44eba50e1365b9e7bb9c5c244afe96a627a28
Python 3.10.10, Qt 5.15.8, Coin 4.0.0, Vtk 9.1.0, OCC 7.6.3
Locale: C/Default (C)
Installed mods: 
  * freecad.gears-master 1.0.0
  * FreeCAD_Assembly4-master 0.12.4
  * freecad-slic3r-tools-master
  * fasteners 0.3.40

The design

I started with a study of the escapement with multiple parts in Part Design to get a first working prototype
Once I had the idea of what I was looking for, I started an assembly with the Assembly 4 workbench
The first part of the assembly is actually only a collection of sketches, some from my first prototype to use as reference, then adding a sketch for the layout of gears.
These 2 sketches are also use for attaching all the LCS in the assembly,
Every part also has a dedicated sketch to attach a LCS if not at the origin. I usually attach to a circle, it is easyer to select than a vertex!
This prevent topological issue with the LCS when editing parts
With all the references sketch in the “BodyLayout” part, I used a lot of : Duplicate selection in Edit menu t have matching parts and dimensions
With this function it is easy to copy a sketch from part to another
Some parts where imported in the assembly “Parts” container, others are designed in context
The gears are first designed in a separate assembly to validate dimensions and backlash, then imported in the assembly, a boolean operation joins the gear with other parts, or two gears togheter, as needed. More on gears to come

Challenges and solutions:
Topological issues are mostly avoided by always using sketches as reference for parts feature and LCS. Sometimes the sketch are offset, or moved using the data property values.
A couple DatumPlane have also been used when needed.
The top plate chanfer took a few tries to get it right, I started with a spline for the holes in the plate, then switched to a series of arcs instead. Of course, by aware chanfer are not topo safe, use them last!
I also wanted to export the file in a STEP format, and had to make the spiral spring square, and fix a few appearance colors issues.

The final touch
Adding the hardware, the screws are roughly placed with transform feature, it is good enough for the visual, only thee visible hardware was added.
Added the piano wire steel springs for a realistic model, as well as the balance shaft and pins
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