[SOLVED] Cannot modify the step-over of the helix

[Giulio Buccini]

Hello everybody,

I would to mill some holes in an alu-plate by using the helix-path.
Quite strangerly, I cannot tune the step-over of the helix (i.e. the inclination of path while digging into the material).

I created a simple plate by using the Path Workbench for posting it here as an example... and I discovered a second problem also: I cannot apply the helix-path to all of the three holes.
I do not know the reason, but even if I select the circle at the bottom of the third hole, the Path workbench generate the toolpath only for the first two holes:

Selection_7791.jpg (50.17 KiB) Viewed 1427 times

About the step-over: the GUI dialog pop-up with 1% as default, I tried all values from 1 to 100, but the toolpath doesn't change.

What's going on?
I attach the example file.

Code: Select all

OS: Ubuntu 16.04.7 LTS (XFCE/xfce)
Word size of FreeCAD: 64-bit
Version: 0.20.28647 (Git) AppImage
Build type: Release
Branch: (HEAD detached at 1c1743b)
Hash: 1c1743b67d209f2b6501de4f75645a33b69d1c31
Python 3.9.12, Qt 5.12.9, Coin 4.0.0, OCC 7.5.3
Locale: English/United States (en_US) [ OS: English/United States (en_US) ]
Installed mods: 
  * fasteners 0.3.40
  * A2plus 0.4.56
  * toSketch

[Giulio Buccini]

Just an additional info here about the second problem.

On my original object, a toolpath is generated for every hole without problems (by selecting just one hole only).

Selection_7792.jpg (40.44 KiB) Viewed 1417 times

[Giulio Buccini]

The second problem can be easily solved by manually adding the missing geometry.
(Base Geometry tab -> select the geometry -> "Add" button)
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Selection_7793.jpg (33.08 KiB) Viewed 1376 times

[chrisb]

You can add the third hole manually to the BaseGeometry.

The stepover seems to be indeed buggy. It works correctly if the radius of the holes is greater then twice the diameter of the tool. In this case that means it must be greater than 6mm for the 3 mm tool.

[Giulio Buccini]

You can add the third hole manually to the BaseGeometry.

Exactly, as depicted in my post above.

The stepover seems to be indeed buggy. It works correctly if the radius of the holes is greater then twice the diameter of the tool. In this case that means it must be greater than 6mm for the 3 mm tool.

This is partially true.
As I can see, the "Step over percent" parameter makes nothing. My tool diameter is 3 mm, and the hole diameter is 8 mm...

I solved in a different way: I discovered that the parameter "Step down" in the "Depths" tab is the only one influencing the step-over.
Here below I set the step-down to 2 mm and the spiral path has changed accordingly:
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Selection_7794.jpg (38.68 KiB) Viewed 1363 times

Here the modified helix:
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Selection_7795.jpg (32.37 KiB) Viewed 1363 times

I think it would be better to make a choice: keep the "Step over percent" and delete/disable the "Step down" parameter, or viceversa.
Alternatively, it would be better if the the percentage field could activate a "macro" modifying the "Step-down" parameter.

In this way the user could choose the preferred way to set the step-over: as tool diameter percentage, or as an absolute vertical measure.

[bmsaus4ax]

The stepover seems to be indeed buggy. It works correctly if the radius of the holes is greater then twice the diameter of the tool. In this case that means it must be greater than 6mm for the 3 mm tool.

I think it would be better to make a choice: keep the "Step over percent" and delete/disable the "Step down" parameter, or viceversa.
Alternatively, it would be better if the the percentage field could activate a "macro" modifying the "Step-down" parameter.

In this way the user could choose the preferred way to set the step-over: as tool diameter percentage, or as an absolute vertical measure.

Step-over works as it does in any other operation, i.e., Radial offset of passes. It is activated by setting a Start Radius in the Properties tab
A setting of say; Start Radius=0.05mm, and Start Side = Inside, and Step Over = 30 will clear the full diameter with 30% cutter step over per pass.

The start radius parameter is a bit odd in that is seems to be the radius of the remaining centre rather than the cutter path radius. Start Radius =1 will leave an island in the middle of the hole!

Step Down is the feed on Z-axis per revolution, also the same as any other operation.

[Giulio Buccini]

Step-over works as it does in any other operation, i.e., Radial offset of passes. It is activated by setting a Start Radius in the Properties tab
A setting of say; Start Radius=0.05mm, and Start Side = Inside, and Step Over = 30 will clear the full diameter with 30% cutter step over per pass.

The start radius parameter is a bit odd in that is seems to be the radius of the remaining centre rather than the cutter path radius. Start Radius =1 will leave an island in the middle of the hole!

From where you know such secrets???
I was not aware of the existence of the "start radius"...
Anyway... SOLVED!

(Here below an example with "Start Radius" = 0.001 and "Step Over" = 60 - I don't like that horizontal G0 movement when milling the second helix, but... it is what it is.)

Selection_7796.jpg (28.42 KiB) Viewed 1320 times

A question: what is the difference between "start side" = Inside or Outside for cylindrical pockets? I see no difference in the resulting toolpaths in my example (you find the attached file some posts above).

[Giulio Buccini]

A question: what is the difference between "start side" = Inside or Outside for cylindrical pockets? I see no difference in the resulting toolpaths in my example (you find the attached file some posts above).

Got it!
Changes the milling order of the helixes, i.e. start side = Outside starts milling the helix more far away from the center first, and then the other ones more close to the center.

[chrisb]

The start radius parameter is a bit odd in that is seems to be the radius of the remaining centre rather than the cutter path radius. Start Radius =1 will leave an island in the middle of the hole!

A start radius of 0 or even less than 0 should be possible.

[bmsaus4ax]

From where you know such secrets???

I've found with FreeCAD as it is developing you have be that annoying kid who pushes every button to see what it does. The documentation does not keep up with the progress.

A question: what is the difference between "start side" = Inside or Outside for cylindrical pockets? I see no difference in the resulting toolpaths in my example (you find the attached file some posts above).

If you slow down the simulation with the Speed bar to near zero you should see the paths start near the centre and progress outward for Start Inside, and hole edge to centre for Start Outside.