How I mill a concave zone?

[Giulio Buccini]

With a couple of minor tweaks the operation you have in your uploaded file can do it all in one pass.

Do you mean by using a 3D-Surface operation? (As suggested by Russel also.)
In the above example I used a 3D-Pocket operation, and I cannot find the parameters you mentioning about.

[Giulio Buccini]

You do not have to do it in one pass. You can set the depth of each pass to whichever depth you want. Say e.g. 0.5mm per pass (See file attached).

Cool!
I was thinking about that one minute ago... you're perfectly right. This could be a smart approach!

Maybe a TiSin coated ball-mill could do the job on alu with low effort (I do not have a lubricating system yet).

UPDATE:
I would add some tolerance (0.1 mm) to the nominal diameter of 12 mm (i.e. 12.1 mm). This could be a problem because it is almost impossible to find a ball-mill with such specific diameter.
As workaround I could make some additional passes to enlarge the semicircle, but the obtained geometry would be not really circular... hmmmm.... (I'm scraping my head).

[Samu]

You do not have to do it in one pass. You can set the depth of each pass to whichever depth you want. Say e.g. 0.5mm per pass (See file attached).

Cool!
I was thinking about that one minute ago... you're perfectly right. This could be a smart approach!

Maybe a TiSin coated ball-mill could do the job on alu with low effort (I do not have a lubricating system yet).

UPDATE:
I would add some tolerance (0.1 mm) to the nominal diameter of 12 mm (i.e. 12.1 mm). This could be a problem because it is almost impossible to find a ball-mill with such specific diameter.
As workaround I could make some additional passes to enlarge the semicircle, but the obtained geometry would be not really circular... hmmmm.... (I'm scraping my head).

I don't know how many of these you want to manufacture but you can get you a tool bit made. I see you are in Munich. Just google for 'Fräser nach Zeichnung' or something similar.

https://www.mack-schleiftechnik.de/de/sonderwerkzeuge
https://www.wema-zerspanungswerkzeuge.d ... zeuge.html

[Giulio Buccini]

Maybe I can simply make three additional passes shifting down/left/right the toolpath of 0.05 mm (i.e. half tenth)?
Yeah, I will not get a perfect circular path, but I think I will obtain a good clamping force over a 12mm pipe in any case... or not?

I plan to make a couple of hundreds of this little boy.

[bmsaus4ax]

With a couple of minor tweaks the operation you have in your uploaded file can do it all in one pass.

Do you mean by using a 3D-Surface operation? (As suggested by Russel also.)
In the above example I used a 3D-Pocket operation, and I cannot find the parameters you mentioning about.

The original file of yours I downloaded was for a 3D Surface. ( mill_test )
The parameters are available by highlighting the Surface operation, and selecting Data Tab.
If you right mouse click in this area and select Show All checkbox you will also see extra parameters that are not normally visible.

[Giulio Buccini]

I explored the solution proposed by bmsaus4ax and Russel (i.e. a 3D surface operation), unfortunately they have both the same defect: the use of a ball nose bit like... a drill.
.
.

Selection_7817.jpg (43.21 KiB) Viewed 938 times

In some moments the bit is plunged vertically into the material, with side effects on the wearing of the tool and heat production. This kind of tool are not designed for such operation. They prefer side-cutting.

Obviously I could cut the rectangular "trench" around the object before cutting the semicircle, but in any case half of the tool will be plunged directly into material (and it will be a little bit deflected also).

So the 3D surface is a no-go option for me.

So it seems that Path does not offer any chance to "enter" into the material from the side...

[bmsaus4ax]

I explored the solution proposed by bmsaus4ax and Russel (i.e. a 3D surface operation), unfortunately they have both the same defect: the use of a ball nose bit like... a drill.
.

So the 3D surface is a no-go option for me.

So it seems that Path does not offer any chance to "enter" into the material from the side...

Attached is a copy of your original file with the suggested modifications for both 8mm and 3mm ball endmills.
The path direction is still the same as your original file too, your Surface operation is unchanged.

If you want to approach the side with less than half of the cutter just increase the Boundary Adjustment, this will move the cutter and give initial paths using the radius edge of the ball. ( or turn Boundary Enforcement off and enter from the full radius outside the shape )

I have not included the Zig-Zag pattern but that is just a matter of selection and will reduce the relocation moves.

[Samu]

Maybe I can simply make three additional passes shifting down/left/right the toolpath of 0.05 mm (i.e. half tenth)?
Yeah, I will not get a perfect circular path, but I think I will obtain a good clamping force over a 12mm pipe in any case... or not?

I plan to make a couple of hundreds of this little boy.

The additional passes should do the trick. Shifting down is easy, just adjust the 'Final Depth' accordingly. For the passes left and right I am not aware of a solution in FreeCAD. I would just edit the trajectories into my gcode manually. If you need help with that, I'm happy to assist.
As for the clamping force - just give it a try.

[Giulio Buccini]

Editing the gcode to add additional passes left/right/down is not a big problem for me.
With time I learned to use Freecad/Path just as tool to produce the "hardcore" gcode, and then to refine it with manual post-processing.

I already contacted a paar of vendors providing "customized" end-mills. I have no idea about the costs for a couple of 12.1 mm diameter ball-nose bits. My max budget is around 200 EUR. Honestly I think they will ask much more than that...

[Giulio Buccini]

If you want to approach the side with less than half of the cutter just increase the Boundary Adjustment, this will move the cutter and give initial paths using the radius edge of the ball. ( or turn Boundary Enforcement off and enter from the full radius outside the shape )

I have already explored that option while playing with 3D-Surface params.

It doesn't fully satisfied me because the path is not straight at the ends. I strongly suspect that it will produce a not "nice-looking" edge, as well as a lot of deburring work for me as the tool will get gradually weared with time...

For automated deburring I'm using a silicon carbide brush by Garant. It provides amazing results, but the edges must be previously well defined by the milling bit.