[Puzzdre]

With dremel you go as deep as needed to remove the walls between holes, not cutting deeper into the block, leaving the little conical pits made by drill bit head. In blocks I drilled so far, the holes are (more or less accurately) 4 mm deep (thx #Rotor!), so it leave you 6 mm for base thickness. Cutting the thin walls is relatively easy, but cutting into the solid block with dremel is...