Tapered Profile

[Russ4262]

Good Afternoon I'm still having problems with this 3d surface for the top of this job, I thought this would be the easy part of machineing this cowl but I am trying to avoid cutting the boss in the middle, this is because that is how I have it fixed to the table with a bolt through the center. I have only face 1 and 8 selected but freecad insists on machining face 10, the boss, even though the boss is higher than the start depth. CowlTopSlice.PNG

CowlTop Slice.FCStd

Afternoon sir.
In your particular case here, you should select (in this order): the outer curved disc ring, the inner lower, flat ring with the four mounting holes in it, and lastly the inner raised face. Then, change the `Avoid Last X Faces` property to a value to 1. This property is available in the Task Panel and the property list of the Data tab once the operation is created. This tells the op that you want to actually avoid the last 1 face(s) in the selection list as ordered. Since the last 1 face is as you call, `the boss`, then the op treats it as a no-cut zone.

Cheers,
Russell

[Joneb]

Thankyou Russell Easy when you know how.

Just for interest the 3d surface path gave some strange code on my model, see lines 513 to 3090 did I do something wrong.

CowlTest.txt

see lines 513-3090

(1.38 MiB) Downloaded 50 times

CowSketchSlice8c.FCStd

(1.4 MiB) Downloaded 35 times

When touching off a 10mm round nose bit should I touch off with the tip or -5mm.

The finished job

image12.png (1.25 MiB) Viewed 800 times

Thankyou again Russell and have a good day

OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.20.24693 (Git)
Build type: Release
Branch: master
Hash: e01f0d25d5f3ef9ceb66aa087212121e9f2f2e8b
Python version: 3.8.8
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.1
Locale: English/United Kingdom (en_GB)

[Russ4262]

...
Just for interest the 3d surface path gave some strange code on my model, see lines 513 to 3090 did I do something wrong.CowlTest.txt
...
When touching off a 10mm round nose bit should I touch off with the tip or -5mm.
...

Morning sir.
Great project! Thanks for sharing the results with forum visitors. Please forgive me if my tone is less than kind or helpful. I am still learning FreeCAD as well.

Re: ring of vertical zig-zags that appear in gcode at referenced lines
The short version is that this is likely a bug in the cut-region assembly algorithm. I will have to add this to the list of bugs for 3D Surface. These 'soldiers' as I call them, borrowing them from the masonry industry and a course of bricks laid in a standing orientation, are caused by the interaction of a round bit interacting with a triangulated vertical cylinder. Good news is we can get rid of them in your project with a few changes to the settings.

The fix:
1. Only select the outer ring face you want surfaced and create the 3D Surface operation.
2. In the 'Selected Geometry Settings' section of the Properties list, leave `Avoid Last X_ Faces` as 0.
3. In the same section, change `Internal Features Cut` to False. This tells FreeCAD to ignore this inner circle in the face you selected.
4. In the same section, change `Internal Features Adjustment` to say 5.0 mm (tool radius) to allow the cutter access further into this internal region.
This will yield the nice clean cut you desire for that outer face. See attached image.

Re: touching off
I think you would still touch tip to 0mm regardless of the bit used. I have very, very little experience with actual CNC usage, so I recommend seeking confirmation from someone besides me on this issue.

Thanks for helping make FreeCAD better and sharing your project results. Makes the involvement all the better.
Have a fantastic Sunday!

Russell

[Steveco]

When using a round nose bit I touch off with the tip, the same as when using a regular end mill and as when using a drill bit.