Thickness sander upgrade II

In order to fasten the paper better, I made the groove and fitted an
aluminium profile with threaded inserts. A piece from the mini drill
press holds the drill far better than it was before.

I took some pieces down to thickness. In one hour it was as follows:
- Top, sides and back for a mahogany soprano
- Back and sides for a mahogany sop that will have a cedar top
- A one piece rim of wenge for a tenor
- Three cherry sides for piccolo ukes
- One walnut fretboard

Whew!