A newbie question about vertical feeds

[falviani]

Hi All,

My setup:
OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.17352 (Git)
Build type: Release
Branch: master
Hash: ec0049921b813ee78c1fd4ea304e70904a3208f7
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United States (en_US)

In order to better understand how the various heights are related in freeCAD, I created a very simple project consisting of a block with a 2mm deep pocket in it (all created in the parts design workbench). The tool is a simple endmill; horizontal feed=5mm, vertical feed=0.5mm, spindle=5000.

The operation is a pocket shape for a simple rectangle 2mm deep. When I looked at the generated gcode (grbl post processor) I was surprised at how it traveled vertically. [I changed the extension of the output file to *.txt so I could attach it; it doesn't recognize *.nc]. Just showing the first line at each level:
G1 X57.868 Y22.704 Z0.500 F30.000
G1 X24.714 Y44.704 Z0.000 F30.000
G1 X57.868 Y22.704 Z-0.500 F30.000
G1 X24.714 Y44.704 Z-2.000 F30.000

Why did the feed change from -0.5 to -1.5 for the last cut? I was expecting a uniform series of cuts 0.5 mm deep. And the finish depth was -1.5, with a final depth of -2.0 - I thought that was how you set up for a nice finishing cut to smooth out the pocket?

Thanks in advance for your clarifications - Frank

[mlampert]

Why did the feed change from -0.5 to -1.5 for the last cut? I was expecting a uniform series of cuts 0.5 mm deep. And the finish depth was -1.5, with a final depth of -2.0 - I thought that was how you set up for a nice finishing cut to smooth out the pocket?

It's because you told it to do so by setting the "Finish Depth" to 1.5 - if you don't specify that (leave it at the default 0 value) you'll get what you expected. For some reason the tooltips aren't showing up - the one for "Finish Depth" says:

"Depth of the final cut of the operation. Can be used to produce a cleaner finish."

[falviani]

Thank you! That did what I expected, so I'll continue setting cuts up that way. I also switched to the ZigZagOffset pattern to clean up the perimeter.

I'm a little puzzled about why my earlier approach yielded odd cutting depths, but I won't lose any sleep over the unexplained

Again, thanks - Frank