Weirdly unreliable 2D pocketing

[stiller7563K]

Here's my situation: I'm still learning, and have given myself the very basic project of milling a tiny drawer for holding marbles. I plan to contour the pieces out of a single small sheet of hobby wood. The front wall has a divot for your finger to pull out the drawer, and the remaining pieces are just rectangles. Generating the gcode from a 2D Contour works like a champ. This is the sort of thing that makes me immediately recognize Fusion 360's usefulness.

Here's the rub. On each of the side walls, I want to pocket out a 6mm by 2mm hole, so I can glue in small magnets. This should be a snap. I've extruded my two holes. Everything on my display looks perfect. I apply a 2D Pocket and select the desired geometry, but for reasons I can't begin to fathom, Fusion refuses to generate the necessary toolpaths. Won't simulate the cut—simply will not recognize these pockets.

I've read the docs, have looked at YouTube videos, and have even started a new file to practice pocketing exclusively. Maddeningly, pocketing works without a hitch in my stand-alone test case. I draw a rectangle, extrude it, and then extrude a circular pit. I 2D Pocket it, and have also tried 2D Adaptive Clearing, and both strategies work instantly. So far, so good, right? So I copy that success and duplicate it next to itself within the same new test file. Even with two, pocketing/clearing gives perfect success! To my newbie thinking, this is the same thing I've done in the original file.

I must be missing *something*. Does anyone have any thoughts as to what?

[stiller7563K]

Update: I feel like I'm getting closer to an answer, but this journey is still very puzzling to me. The reason my test case worked is because the hole's diameter was bigger than in my actual file. In my test case, I just quickly slapped down a rectangle and extruded in a 12mm hole (or 24mm, or whatever I happened to draw). These always work fine. In my actual file, the hole—or maybe the correct term is pocket, because I don't mean for this pit to go all the way through—is only 6mm, to fit my 6mm magnets.

For this particular procedure, I'm using a 3.175mm flat end bit. That should be fine, right? The bit is still smaller than the hole, by half. In my test case, as I reduced the diameter of the hole/pocket/pit, everything worked at 12mm, 10mm, and 8mm. As soon as I reduced it to 6mm, no dice. Suddenly, neither a 2D Pocket nor a 2D Adaptive Clearing would work. But shouldn't it?

Do I really need to use a tiny bit, like a 1mm flat end, to pocket something 6mm in diameter?

[stiller7563K · Accepted solution]

Update 2: All right, I'm just going to try to be Zen about this. The answer, indeed, seems to be to use a smaller bit. Luckily, I have a few that are pretty small. When I select a 2.4mm bit, this does now seem to work, both for pocketing and for adaptive clearing.

IMPORTANT: I have to make sure to set my Bottom Height to "Selected contour(s)," otherwise the hole would go all the way through. This is confusing to me, as normally I set my Bottom Height to the bottom of my model or stock—which, I would swear, is what I did for the larger diameter test cases. To my thinking, Fusion should understand that I mean "go only 2mm down" when I select the bottom of the hole/pit in the Geometry tab—when the bottom of the hole is in fact only 2mm down. Again, I'm 99% sure that's how I did my larger diameter test cases, so I'm shrugging and moving on.

At least I'm rolling again! I'm posting replies to my own question in hopes it helps someone else in my situation.

[johnswetz1982]

Your picking a [2D Pocket] so it is not model aware and does not know how far to go down, that is why you have to specify it.

The issue with your pocket not working is beside the diameter of the tool you also have to take into account the ramp diameter (red helix) and the lead-in value so a 6mm bit might cut a 9mm hole at the smallest. the values are just examples, you can get different ones by messing with the values on the linking tab. 

[stiller7563K]

Thanks for the insight, johnswetz1982! I'll bear this in mind, moving forward. I'm finding the learning curve steep here, but I'm sure it'll be worth it as I progress. I appreciate when a software vendor offers support forums, for exchanges exactly like this.