I've now turned the top upside down. and it is time to use a 45 degree bit to bevel the underside of the opening.

I went to Home Depot, bought the router bit, a Diablo 45 degree 5/8" Cut Length Chamfer Bit, #DDR40-106, came home, tried to install it, and it didn't fit - the opening in the router base plate was about 1/64" too small. I fully extended the router base, removed the locking nut, put the bit shank through the nut under the base plate and assembled everything. It took some jockeying around to get everything to go together, but it does fit. I then turned on the router and slowly lowered the base as the bit cut a larger hole for itself. it worked perfectly!!! :-)

I had been buying my carbide router bits from MLCS - the Katana carbide router bits; however, I didn't have time to wait for shipping today. I went to Home Depot and bought the only suitable bit that they had, and it filled my needs admirably! I did not want a sharp edge on the top of the opening for the sanding drum. As luck would have it, and it was exactly that - dumb luck, this router bit provided me with exactly the end result that I was looking for - a short vertical support of plywood running the length of the opening under the laminate. Recently someone put me on to Whiteside Machinery router bits. I've got my first in, and it is a honey :-) Since writing this I have bought 5 or 6 more Whiteside router bits, and I am impressed with them.

Thin cuts were made so as to not overload this small router. It was a breeze :-)

You can see one of my mistakes while using the table saw - I went too far with the cut. I did the same thing with the router bit (lower left corner of photo), as you can see, but it's no big deal as it doesn't show from the top.

Now I need to square out the corners a wee bit.

One of the things that I noticed on the YouTube video series about making a V-Drum Sander is that the maker made a bit of a deal about making the opening "just right" so as to be able to sand small pieces. This necessitated a table saw and a handsaw. I found that the 45 degree router bit makes a suitable opening. I also left a small vertical surface rather than feather out the top edges which I simply did not like. I preferred some additional support under the top laminate around the opening as laminate by itself left unsupported is too easily broken.