Coving the interior
Coving the interior is not difficult provided that all the box faces are parallel. I designed this box with a 10 degree angle on the right face – to make it easier to get to the amp controls, and also initially to create a non-parallel face for less resonance. I designed it this way before I settled on the coving method – I would never have an angled face again if I was coving the interior, some of the cuts were very difficult!
First I glued in all the corner coves on the bottom area, then cut and glued in the straight coves along the bottom corners. Both the corner coves and the straight coves have the same radius, so they match up well.
Filling around the speaker opening was.. er… fun. Fortunately the straight coving is about the same radius as the speaker driver so I could mangle 2 pieces together to make this piece (with a bit added in here and there). I also made the mistake of placing the speaker opening a couple inches farther right than I intended (the curse of more than one set of plans lying around…) This made it a bit more challenging than otherwise.
Now the bottom coves have been finished, and the top coves are in place:
This is a look in through the speaker opening at a top cove.
Now most of the top coving is in place. Typically I would apply the glue, dampen the other part with a sponge, place the part, and tack it with a few brads.
Now there is just one straight cove left to install. You can see I used masking tape to keep the glue foam-out in check. The buildup of wood around the bottom is actually around the speaker opening.
Now all the coving is in place. The inside has been evened up using a 36 grit flap wheel on an angle grinder, then the inside was primed to seal up any pinholes.
And finally all the crevices behind the coving have been filled with about 95 pounds of dried sand (in the bottom crevices too). The sand was dried in the oven in 4 batches in a large cast iron pot… This view is looking down at the top of the cabinet. I did a dry fit to make sure the top fit before this… Gorilla Glue was then generously applied to all the mating surfaces, and especially around the center area where the coving meets the top face.
And finally the top has been glued in place.
I then cut a rabbit around each edge using my router and a top-bearing-flush-trim-bit, and inserted some hardwood trim. The trim was then flushed to the faces using a low angle block plane, and then rounded over again with a cove bit, and finally the outside corners were rounded. (not shown here).