Intact examples of viking round shields recovered from the Gokstad ship were 94 cm across and made from a single layer of planks, about 7 mm at the center. My question is, how would meter-long planks as thin as 7 mm have been manufactured with techniques of that period?
Vikings and early medieval Scandinavians used wooden wedges and hammers to split tree trunks and then broad-bladed axes called "timmerbila" or "skrädyxa" to spliter off planks or smoothen existing planks.
"Kulturen" in Lund, Sweden is an association that uses experimental archeology to recreate medieval and early modern carpentry. Among other things they have constructed a wooden stave church with early medieval methods and tools.
Here you can see them in action splintering a log.
Here you can see them making staves for the church (speech is in Swedish, but it is mostly action.