FreeCad Gear Box

What

This is a little record of my work to make and print a gearbox using FreeCad

A Python Helper Program

In my approach to the problem each part needs to be positioned ( so far in the z axis ) so that all the parts come together correctly. I started to do this by making a sketch of a side view of the gearbox ( will add here later ). Then I began a spreadsheet of the z positions. I do not really like spreadsheets because I find them very error prone and compared to programming a bit tedious. So I wrote a Python program. Initially I just set up a large number of variables and did the math. This was using Python as pretty much a general purpose calculator. Then I began to see a pattern in the calculations.

A Pattern

The pattern goes like this:

• Each part has a bunch of values that effect z positions
  • Bottom of the part.
  • Thickness of the part.
  • Midpoint of the part.
  • Top of the part.
• Clearly there are some simple relations between these values.
• Parts are often stacked up. In the gear box:
  • Bottom plate
  • Washer
  • Spacer
  • Lower Gear
  • Upper Gear
  • Spacer
  • Washer
  • Upper Plate
• Some calculations:
  • A part's bottom z position + part's thichness = part's top z position
  • One part's top z position becomes the next part's bottom z position.

Pattern into Python

Two classes have been found useful so far.

• Part3D
• PartStack