FreeCad and V-bits

 This year has brought changes to Autodesk's free subscriptions.  These changes along with a general dislike of software as a service have me looking for a Fusion 360 alternative.  I gave FreeCad a brief look in the past but the CAM tools were too limited for some of my projects.  FC v0.19 is now near official release with a larger variety of tool path operations.  Some bugs remain and some things are a bit clumsy but it's becoming a legitimate alternative.  

The Path workbench creates the everyday tool paths in the usual kind of way and these are reasonably well documented.  In an effort to better understand FreeCad I'm testing some of the less commonly used path tools.  My experiments will be recorded here as notes to myself.  If they are useful to anyone else you're welcome and thanks for reading.

First up is the v-carve operation but not used in the way FreeCad intended.  The goal is combining v-carve with other tool paths to create inlays using the methods employed by F-engrave.  This has been an adventure and my respect for F-engrave has increased in the process.  This is no knock on FreeCad, Scorch's software is specialized and what it does it does very well.

FreeCad's v-carve tool path works on the concept of fitting a circular diameter to a face shape of various widths.  For example a face width of 0.100" will require a 60 degree v-bit to a depth of 0.0866".

The math in this example is pretty basic.

(0.100/2) / tan30 = 0.0866

and at full depth

(0.250/2) / tan30 = 0.2165

These numbers describe a 0.25" 60 degree v-bit

The description above is of course an over simplified description of the concept.  I believe in reality some fancy math is used involving something called Voronoi Nodes. 

Testing the numbers above on a 0.100" wide face returned weird results.  I discovered that the tool editor has bad labelling for the included angle definition.  To properly describe a 60 degree included angle cutter the value to enter in the tool editor is 120.

The math is 180 - included_angle.  ***

Another oddity, possibly connected to the glitch above,  is the connection between tool diameter and depth of cut limit.  To enable full depth of cut the tool diameter must be defined larger than actual size.   Watch out for this if intending deep cuts.

*** FC v0.19 will have a new tool bit system so these problems may only apply to the legacy tool system.  The release of v0.19 is expected by the end of 2020.

The v-carve operation includes options Discretize, Threshold and Tolerance.  I have been unable to find good definitions for these options and they may not be fully developed at this time.  The FC wiki has an example of using v-carve but these options are not described there.

Are inlays possible using FreeCad ?

Yes and No.

That's the next post.