Originally Posted by Favelle
So is there a special kind of Bondo for wood? Or can I go to NAPA and just get automobile Bondo?
Yes, the least expensive lightweight bondo from there or the hardware store is fine.
If you haven't built the cabinet yet, avoiding screws and just clamping up the assembly would be better for a piano black finish. As mentioned, if fasteners have to be used, a small finish nailer will be much better.
Also, miter all the joints so no MDF edges are exposed where they might be seen. The different texture, expansion, and factory finish makes it much harder to hide under the finish.
Layering a few coats of epoxy like the Abatron product will help provide a harder, sealed, and smoother base(if sanded with leveling blocks and pads) for the primer/paint/clearcoats to be sprayed. You will still have multiple coats to spray as mentioned previously, with sanding/leveling inbetween coats. A good worklight that can be moved and adjusted will help, using it from the side to highlight imperfections in the surface currently being worked on.