I did a few finger joint projects using Fusion 360 shortly after I finished my Burly. I found it to be a frustrating experience, and I never got to the point where I had a parameterized Fusion 360 setup, nor where I was able to easily repeat the joints. Lately I’ve done a bunch of finger joint projects using my laser (on the Primo)…over 30 to date, and these projects have made me want to revisit routed finger joints.
Looking at your pictures:
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Given the wonky edges on some of the fingers, I suspect a mechanical issue with your machine. Shortly after upgrading to a Primo, I found my core clamps loose, giving me inconsistent cutting. Later, I had issues creep back in, and I found a broken core clamp (probably overtightened it).
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Once you have the wonkiness figured out, I suggest you do some test cutting. Model two, small pieces with just two fingers each. Cut out the pieces and measure the result with calipers. If everything is working correctly, and you’ve set up the toolpaths in Fusions 360 correctly, the width of the fingers, and the width of the slots should nearly match, and the width of the finger should be very close to the size you modeled in Fusion 360. If they are not nearly the same size, you will have to do some exploring to figure out the issue.
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A near match in size will not allow your finger joints to push together. You need some tolerance in the finger joints in order for them to fit together. Some tutorials indicate the tolerance should be modeled into the design. I tried this, and, when I got the tolerance right, the joint worked, but it seemed like a lot of work in Fusion 360. Another thing I tried was using negative stock to leave in the contour tool path to create tolerance. This works, but it also shortened the fingers by the tolerance amount. If that is important, you may have to model the fingers a bit longer than the width of the material to allow for the extra material removed due to a negative stock-to-leave setting.
If you cannot get a near match in finger width wrt the model size and the size of the slots, author the cut of a simple square. Look at the g-code of that square you’d specified in Fusion 360 and make sure the g-code is cutting a square of the proper size. In doing this calculation, you need to take into account the diameter of the router bit.