December 29, 2020

3D Printing - FreeCAD

I have now printed a bed leveling test and a calibration test cube with success. The calibration cube gave me an introduction to the slicer. The missing ingredient now is some kind of CAD software (unless I just want to print files downloaded from other people's designs).

My friend Dave recommended TinkerCAD, which is an easy to use online web-based tool. The page that offered me the xyz test cube mentioned that the test cube was generated as part of a tutorial for freecad. I would actually like to use CAD software hosted on my local machine, and FreeCAD is available as a package download for Fedora, so .... 

su
dnf -y install freecad
It is just that simple. Typing freecad fails though. I search through the XFCE application menus and find it under "Education" and drag it to be a shortcut next to the small handful of shortcuts I have set up. Some investigation reveals that the /bin/FreeCAD binary is what gets run, so I make a linke in /usr/local/bin named "freecad" since I am not going to put up with this silly mixed case business and wear out my shift key. Here is the tutorial on the calibration cube. A big part of the tutorial is using Inkscape to generate the letters.

Make a brick

The first tip in the tutorial is the Freecad has multiple workbenches with different tools and I want the Part workbench. This is selected by the one menu like field at the top center. Given this, it is easy to select the cube and click on the workspace to place it.

I go to Edit -- Preferences and change units from MKS (metric) to US (in/lb) so now I see units in inches. I click on the cube in the "labels and attributes" columns on the left and this gives me properties which I an edit. I change the dimensions to 1 by 0.5 by 0.25 tall. Now I use File -- Export, give it the name "brick", select STL in the long menu below and voila. I have the STL file.

Note that infill is a job for the slicer. If you want solid plastic, you select 100 percent infill. I go to Cura, and use open file, but this places it alongside the calibration cube I just printed. New Project is the cure, this cleans things out and gets Cura ready for something new. I do Open file again, Slice with 20 percent infill, and I am ready to go with a 10 minute print.

Make a brick with a hole

Now you have to draw a circle on the face of the brick using "Sketcher" or perhaps "Draft" and then go back to Part and extend that 2D thing on the face into a pocket or hole. Sketcher has no sensible way to simple specify the coordinates of the center of the hole, it has a crazy concept of constraints, which is totally non-intuitive. Draft will allow you to specify a center point and a radius.

I'll also note that there are issues with using inches. FreeCAD has a metric based design and attempts to show English units, but this is clearly incomplete and buggy. The authors are in Europe and clearly only deal with English units rarely. This might be a tool to simple stick with metric units. I set a grid size in Sketcher and found that I had to exit and restart FreeCAD to see it get applied. When I try to set a grid size in Draft, it only accept mm units, so I must enter 1.27 to get a grid in inches.

My conclusion is that this is not ready for public use. The combination of Sketcher using this bizarre constraint scheme to place circles along with the incomplete ability to deal with English units has already thrown up too many issues to make me want to continue struggling with this. I know I want a 1/4 inch diameter hole centered at 0.25 and 0.25 and I don't want to write mathematical proofs to express myself to this CAD software.

Other options

There is OpenSCAD, which they say is not an interactive tool -- it expects to to "describe" your model rather than draw it. A different approach, but worth taking a look at. One review called it a complicated tool, which is fine as long as the complications are consistent and it doesn't fight english units.

LibreCAD is lightweight and simple, but only 2D, so unsuitable for designing stuff for 3D printing.

Blender also gets mentioned, but it is not really designed for CAD, but some people say it works great for their 3D printing needs. It is a big complex package designed more for art and design than technical CAD work, but if you know it, it can certainly serve well for 3D print design.

Have any comments? Questions? Drop me a line!

Adventures in Computing / [email protected]