Pocket3D Edge with finer tool?

[namezero111111]

Dear folks,

I am new to the Path workbench for CNC, so this might be an X-Y problem.
I am trying to make a 3D Pocket with a large tool using a pass extension.
Then, I would like to go around the outside and use a finer tool and stepdown.
However, how can I restrict the second operation by the first so I don't "cut air" 99% of the time?

Here is an example:
First operation

Capture.JPG (27.79 KiB) Viewed 1864 times

Second operation:

Capture2.JPG (46.07 KiB) Viewed 1864 times

99% op this operation is unnecessary; I just need one or two spiral passes on the outside.
I found that I can use a boundary dress-up, but I cannot bound by the other operation.
What's the correct way to achieve this?

[chrisb]

This is currently not possible.

[namezero111111]

I wonder; can this be hacked with the experimental "3D Surface" to follow a Pocketing Operation?
It appears to give a single pass along the edge:

Capture3.JPG (64.46 KiB) Viewed 1820 times

Following a pocket operation with a rough tool and a finishing 3D Surface - what is the gotcha with this?

[jescombe]

What I tend to do as a workaround (when making inlays with some fine detail around the edges), is to remove the bulk by pocketing with a larger tool, and follow that with an internal profile pass (or two) with a smaller cutter that gets me right into the tight corners. Have to be mindful of the stock that's left, and perhaps adjust the offset a couple of times to clear it all...

[namezero111111]

What I tend to do as a workaround (when making inlays with some fine detail around the edges), is to remove the bulk by pocketing with a larger tool, and follow that with an internal profile pass (or two) with a smaller cutter that gets me right into the tight corners. Have to be mindful of the stock that's left, and perhaps adjust the offset a couple of times to clear it all...

Could you detail how you got this to work for pockets that don't have an even bottom? I might missing something here; I had tried to tinker with profiling, too.

[jescombe]

Could you detail how you got this to work for pockets that don't have an even bottom? I might missing something here; I had tried to tinker with profiling, too.

Ah sorry, I'd missed that rather important point! In that case, I can't see how you would do it either..

[bmsaus4ax]

Dear folks,

I am trying to make a 3D Pocket with a large tool using a pass extension.
Then, I would like to go around the outside and use a finer tool and stepdown.
However, how can I restrict the second operation by the first so I don't "cut air" 99% of the time?

The 3D option is the easiest solution. The first step is to use the Waterline operation. You can use a large Endmill to rough out the bulk of the cavity.
I have experienced an error with this operation but it does not seem to be fatal. It puts the operation into an edit state where the 'Waterline' in the object tree is in a highlight yellow colour with an error in the report window. To get past this, right click on the 'Waterline' and select 'Finish editing' in the dropdown list, this should clear the highlight and from here on it is all happy again.
Probable error ending in

Code: Select all

PathGeom.py", line 91, in isRoughly
    return math.fabs(float1 - float2) <= error
<class 'TypeError'>: unsupported operand type(s) for -: 'float' and 'NoneType'

waterline.png (49.47 KiB) Viewed 1730 times

You can then carry out a 3D Surface operation, single pass, with a ball end mill. My preference is to use the line pattern with a small step over to give a consistent cut pattern to the finish. The default behaviour is to start on the top surface and the follow the curve, but this can be altered in the Data Tab after the operation is created. Under "Selected Geometry Settings" the parameter "Boundary Adjustment" can be changed to minus half the tool diameter and the cut will enter directly into the cavity vertically without going around the top edge.

3Dpath.png (61.5 KiB) Viewed 1730 times

I have used version 0.20 here but version 0.19 will do the same.

OS: Ubuntu 20.04.2 LTS (ubuntu:GNOME/ubuntu)
Word size of FreeCAD: 64-bit
Version: 0.20.24847 (Git) AppImage
Build type: Release
Branch: master
Hash: 20e756306d9aa624fcbf465f0345d721673ce720
Python version: 3.9.2
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.1
Locale: English/Australia (en_AU)

[namezero111111]

The 3D option is the easiest solution. The first step is to use the Waterline operation. You can use a large Endmill to rough out the bulk of the cavity. [...]

This seems to work very well. I gave up on waterline because of I didn't know how to remove that error; thanks for that!
What is the difference of using waterline to 3D Pocket?
It seems like both do the same (or extremely similar things) in this case.

EDIT: Could you double check if your 3D Surface works with a fillet on the top edge? It works for me with a chamfer, but a fillet seems to hang FreeCAD (It's doing something for many minutes and using >25Gb memory) even on an extremely simple model

Generally the 3D Surface seems painfully slow, although the output appears correct.
A message "dropCutterSTL5 129 cl-points and 392784 triangles." even for a simple object is generated. That's 400k almost!
Adding another unrelated fillet to a hole blows this up to 1167312 triangles!
I'm not a pythonist, but maybe in PathSurfaceSupport.py(525) everything is preprocessed before on line 548 everything is processed "as needed"?

[bmsaus4ax]

[
What is the difference of using waterline to 3D Pocket?

I don't know the correct answer, but I would think it is because waterline only follows the wall ( nearer vertical geometry ) not the face as in pocket.

EDIT: Could you double check if your 3D Surface works with a fillet on the top edge? It works for me with a chamfer, but a fillet seems to hang FreeCAD (It's doing something for many minutes and using >25Gb memory) even on an extremely simple model

Generally the 3D Surface seems painfully slow, although the output appears correct. I'm not a pythonist, but maybe in PathSurfaceSupport.py(525) everything is preprocessed before on line 548 everything is processed "as needed"?

That is the key thing about Surface, there is a lot of geometry to process.
The more complicated the path the more time and memory is involved. Both line and circular paths processed for me when 1mm radius included, but the line path takes a significant amount more to process as it produces better detail. I had to 'Wait' through a couple of 'Not Responding' events; processor has 8 cores but not the latest speeds.

radiusSphere.png (66.38 KiB) Viewed 1671 times

circularRadSphere.png (95.39 KiB) Viewed 1671 times

[namezero111111]

Thanks for the tests. It just confuses me that unrelated features (faces far away) have dramatic effects. My assumption was that the bounding box of the relevant object cuts away features that don't matter, but they seem to be processed and then discarded.