The Abacus simply consists of two vertical posts each with four drilled holes to accept the horizontal dowels.
The dowels should be of well seasoned and strong wood to resist warping,
The base can be any shape which you find pleasing, a router will give it the finishing touch on the top edges, two holes are drilled in to the posts.
The beads are turned about five at a time, turning too many at once can lead to errors as could bow slightly in the centre, the hole can be either drilled first before turning which would eliminate handling problems and damage to the bead when the drill breaks through the back end,
Or drilled afterwards by using a jig to hold the breads in a vertical drill press,
Or use a drill mounted chuck and drill half way from both sides to eliminate breakout.
Then fit everything together.