I finally got round to learning to use FreeCAD and making plans.

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The 3D modelling of parts was actually quite easy using FreeCAD 0.19

There is quite a steep learning curve with this software and must admit that I found the Part > Body > Sketch logic difficult to get at first.

But stick with it as it does click, I'm coming at it in middle age and it's taken me ~3days of solid work to get to a point where I can design parts.

I have found the technical drawings quite tedious, it might just be my very low knowledge of CAD...

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I have though created plans for this simple oscillating engine, ok, they are not free, but they are low cost.