When talking about kerf and Fusion 360 I have mentioned a couple of times that kerf is somewhat subjective and the best way I have found to adjust for it is to make a small object that uses the same type of joint as what I plan to use for a larger project.
To use this sort of thing, install DXF for Laser from the Fusion 360 store this will allow you to adjust the kerf quickly and experiment until you have what you want.
The kerfinator I am posting the link to is for box joints but you can use this concept for slot together parts or any number of other joint types. The concept is to simply sacrifice a very small bit of material getting the kerf the way you want it before committing to a large project.
To use this simply open up the parameters box and enter the exact thickness of the material you are using, then click okay. Now click on a face of the model and activate the DXF for Laser plugin. The plugin will bring up a dialog box like you are used to seeing. Input a kerf value and click okay. Do the same for the other part.
Convert the two DFX files to a single SVG. Cut these on a piece of scrap of the type you want to use and test fit them. If you like the fit, you are done. If not, try again adjusting in the direction you want to go. A larger number for a tighter fit, smaller for a looser fit.
Now you can integrate this kerf compensation into a parametric model or simply use DXF for Laser to export faces using the number you came up with.
.21mm is a good starting point for the 
plywoods
Seems to be a problem with Autodesk taking this public so here it is in a zip. Sorry about that. Removed link as this is not going to happen. Please use the zip below.
kerfinator.zip (118.1 KB)
As always, let me know if there are problems or if you find this useful.
