Cut off a 21-in.-long board for the shelves, rip it in the middle to make two shelves, and cut 45-degree bevels on the two long front edges with a router or table saw. Bevel the ends of the other board, cut dadoes, which are grooves cut into the wood with a router or a table saw with a dado blade, cross- wise (cut a dado on scrap and test-fit the shelves first!) and cut it into four narrower boards, two at 1-3/8 in. wide and two at 4 in.
I prefer the large size because it will cut the most sizes. Years ago I purchased a medium shoulder plane, but it didn’t cut the larger sized joints, so I sold it and purchased a large shoulder plane so I could cut and trim most sized joints. Most of your traditional woodworking hand tools can be vintage/used, but used shoulder planes can be very hard to rehab and get “square”, so I recommend spending the extra money on a new shoulder plane. See my recommendations in my hand plane buying guide.
Thickness planer. A thickness planer is used to fix surfaces of imperfect wood. If you are picking up less than perfect wood from the lumberyard, wood with some surface defects, a planer will let you fix that wood in the quickest time. A thickness planer pays for itself quick as it allows you to buy cheaper wood that doesn’t have perfect surfaces and fix it yourself. Be careful though. You loose wood during planing. So the remaining amount of wood still has to be worth the price you paid for it.
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