What's the best way to sketch a shape like this outline?
I've tried using a B-Spline, using eliptical arcs, and making a polygonal approximation and then filleting it but none of them worked well and both were very hard to figure out how to measure for.
6 replies
The best way would be to put this on a 2d scanner, load the image into FreeCAD, scale the image using a known measurement, and then using a spline to draw the outline over the scan (don't forget the symmetry!). Working with splines is a science in and of itself, so you should watch a few tutorials or read the docs.
Ahhhh that seems like a good way to do it I'll try that
Can't say for sure based on a single top down view, but I imagine you want the Curves workbench from the addons manager.
Here's a good tutorial video on it: https://www.youtube.com/watch?v=czp8IPH72-I
edit: Measuring a part like that will always be tricky though. For best results I imagine you'd want a high detail 3D scan or scale photos from various angles taken with a telecentric lens (or a high focal length lens from far away), so you could bring in some to-scale reference geometry to sketch against. Failing that you will probably just have to eyeball it.
I'm only trying to make the top down projection right now because that's the only part that needs to be dimensionally accurate to the original
For just the top-down view I don't think you should have any trouble with just the regular sketcher with splines and/or arcs. Sounds like you're mostly having trouble measuring the part rather than actually sketching it?
If top-down is the only plane you care about then you could try tracing the outline of the part on a sheet of paper and scanning that in using a normal document scanner, or even just scanning the part directly if it fits in the scanner. You can then bring that scan into FreeCAD and use it as a reference and it'll already be at the correct scale.
For making the sketch, make sure you make use of the fact that the part is symmetric and you only have to sketch half of it.
Picture - darktable lens correction - inkscape - import bitmap - trace bitmap - cleanup in inkscape - freecad svg import - symmetrize it. Most of those steps will require manual tweaking.