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Confused about tool diameter

dannybloe
Sat, 27 Feb 2021 16:12:53 GMT

Hi folks, FlatCam newbee here. I am trying to get a proper isolation from my gerber file. In EasyEda I created a copper ground plane with a clearance of 0.5mm and my tracks have a width of 0.5 as well. When I open the file in FlatCam I see a nice space between the track and the ground plane. When moving the cursor over the clearance I can see it is indeed 5mm (by comparing the x/y coordinates shown in FlatCam). Then I create an isolation and I pick a tool of 0.5mm (C1) just to experiment a bit with the settings. I set it to one pass, no overlap and generate the geometry. What I would expect is that the with of the geometry between the track and the ground plane just fills the area (after all, the gap is 0.5mm and the tool diam as well). However, I see this: [Screenshot 2021-02-27 at 17](//muut.com/u/flatcam/s1/:flatcam:tvEq:screenshot20210227at17.06.56.png.jpg) You can see it creates two paths in the clearance while I would expect there to be one. Also, when I set the toolwidth to 0.250mm I would ex pect to see two paths touching each other but I see this: [Screenshot 2021-02-27 at 17](//muut.com/u/flatcam/s1/:flatcam:cyOy:screenshot20210227at17.09.29.png.jpg) As if there is still a gab. What am I missing here? Thanks, Danny

Marius Stanciu
Sat, 27 Feb 2021 16:25:07 GMT

Hi Danny, Each polygon is isolated. Meaning that a path is traced around each polygon (be it a trace, a lone pad, a zone etc) at a distance of half the tool diameter. The path will be therefore at a distance of half of the tool diameter. That is because half the diameter of the tool is to the right of the tool path and half the tool diameter is to the left of the tool path. If you have 2 polygons close to each other, intuitively you will expect to have only one path between those two polygons if you isolate in the conditions you mentioned. But in reality the software will isolate both the polygons and if the conditions are right (like those you mentioned) you will get two overlapped paths. Best regards, Marius

dannybloe
Sat, 27 Feb 2021 16:28:57 GMT

Ehm.. so if I understand it correctly: if my track width is, let's say 0.5mm and I use a tool of 0.5mm to isolate it, then I will end up with no track at all? As, from what I understand, there is an overlap of half the tool-size on both sides of the track.

Marius Stanciu
Sat, 27 Feb 2021 16:30:33 GMT

Nope, because the isolation will be done at a distance of 0.5mm /2 = 0.25mm. Overlapped means that one path is over the other. It will cut twice at the same spot.

dannybloe
Sat, 27 Feb 2021 16:33:35 GMT

I assume 'Nope' means that the track will be completely gone. But, if that's the case, doesn't that defeat the purpose of isolating? After all, I want my track to be 0.5mm wide when the milling is complete. So, I would need a bit of 0mm to make that happen 😉 . Or I must make my tracks 1mm wide in my designs.

Marius Stanciu
Sat, 27 Feb 2021 16:41:19 GMT

No Danny, your assumptions are wrong. When I said 'nope' I meant that what you said was not how things are. A tool path, actually an isolation tool path, is just the path that the center of the tool (a tool that do have a diameter) is following around a certain geometric feature (or said differently, a polygon). When a tool is following that path, half of its dia is to the left and half is to the right isn't it? So, for a clearance of 0.5mm between two traces, a red line (a tool path) done for the tool diameter of 0.5mm will be drawn exactly at the half of the distance between the two traces, meaning at around 0.25mm distance to each trace. When the tool is passing between the 2 traces, following the tool path, it will mill 0.25mm to the left and 0.25mm to the right effectively clearing 0.5mm space of copper which is exactly what you want. I'm sorry but there is no other way that I can explain this. If still have trouble grasping this I think the best way is to actually make a real-life test.

dannybloe
Sat, 27 Feb 2021 16:41:41 GMT

Ah.. I get it. That's indeed what I would expect to happen. I just did another test, this time with a tool of 0.25mm and a clearance of 0.5mm and now I do see what I expect: [Screenshot 2021-02-27 at 17](//muut.com/u/flatcam/s1/:flatcam:UOSZ:screenshot20210227at17.39.09.png.jpg)

dannybloe
Sat, 27 Feb 2021 16:43:30 GMT

As you can see, the blue paths overlap at some points. But it's a pity that many paths overlap. Like the top circle. It's almost visited twice entirely.

Marius Stanciu
Sat, 27 Feb 2021 16:47:20 GMT

The blue paths are meant to show what the end result will be. They do take into the consideration the actual tool diameter. There are some algorithms that I've implemented for rest-machining (first clear with a larger tool what it can do and then try to use smaller tools where the bigger could not work) but that's just a way to minimize (and not completely get rid of) of the ineffectiveness of not-desired overlaps. Those are limitations of how the software is working. I'm afraid we can't do better.

dannybloe
Sat, 27 Feb 2021 16:48:03 GMT

Yeah.. I understand. I'm thinking... I could have the ground pane omitted in the gerber at all. After all, if the traces are isolated you automatically end up with the ground plane anyway. 🙂

Marius Stanciu
Sat, 27 Feb 2021 16:48:45 GMT

You don't have to do something as radical. All you need to do is to not isolate the ground plane.

Marius Stanciu
Sat, 27 Feb 2021 16:49:58 GMT

And that can be done by editing the Isolation geometry and deleting the path surrounding the ground copper pour. You use the Geometry Editor from FlatCAM beta for that.

dannybloe
Sat, 27 Feb 2021 16:53:22 GMT

aha! That's a good tip. Thanks a lot Marius. I will do some more tests tomorrow before I mill my true design.

dannybloe
Sun, 28 Feb 2021 09:58:09 GMT

Mmm.. unfortunately that doesn't work as the ground-pane geometry also holds the isolation geometry for the pins connected to ground. So you end up removing too much. Btw.. there's no undo there so if you remove a geometry too many you have to start all over again.

dannybloe
Sun, 28 Feb 2021 10:16:29 GMT

Oh, nevermind.. I made a mistake in my routing 😉