I never used FreeCad. from my experience with other platforms I would say you need to establish new auxillary planes from which to make your cuts. Send me a PM and I will detail the steps you need to get it done.

GingerLathe's object is trickier than most to 3D model because it has a number of faces that aren't at right angles to each other. As most models are developed at right angles, FreeCAD (and other software) defaults to this, and it's necessary for the modeller to adapt. Jason mentions Alibre's extrude tool can be told to cut at a draft angle, but FreeCAD's equivalent doesn't support that convenience. Instead it's necessary to define planes and cut from them.

This 2D drawing illustrates a knife tool. (Some angles are exaggerated):

The tool is ground to present a sharp edge to the work. Metal is removed to provide clearance to stop the tool rubbing, and more metal is removed 'rake' to sharpen the wedge and improve the cutting action. Rake depends on the material, up to 40° for softer metals like Aluminium, and down to 8° for a high-carbon steel. Mild-steel is in the middle – about 27°. As removing metal to improve cutting action weakens the tool, the angles and amount of metal taken off are carefully controlled in industry to balance cutting rate against tool life. For amateur purposes I see little value in that and just grind roughly to the shape recommended for mild-steel. Approximately!

From top to bottom, GingerLathe's knife tool might be ground by first grinding the Front clearance to create a wedge. My drawing is an exaggeration – 8° is more realistic than 17°!

Next, the top rake : 27° rather than my 6°. As swarf flows over this face, one of my books recommends grinding in the direction swarf travels and then polishing the surface. The lip can be developed or moved forward to act as a chip breaker – useful to stop long ribbons forming.

Finally, front clearance and side rake. These don't seen to be critical other than the angle at the point should be nearly 90° for strength.

I modelling this in FreeCAD by drawing a rectangular blank, defining tilted planes relative to the blank, sketching on the plane and then removing metal along planes with the pocket tool:

The button used to create planes in circled in red. Planes can be rotated (Yaw, Pitch, and Roll) and Moved in X,Y and Z. Modelling the tool needs 3 planes, none of which are at a right angle to the tool blank or to each other. Bit fiddly to set up, but gets easier with practice.

Hope that helps.

Dave

Edited By SillyOldDuffer on 09/02/2021 12:05:52

Another way to do it in Alibre is to make the top-down profile, then create planes along the angle edges at the relief angles and use these to extrude cuts that finish the shape.