The staves or ‘Duigen’ as it is called overhere are actually straight when being made, marked and then put together in the hoops. The best wood would be oak.
![afbeelding](https://global.discourse-cdn.com/sketchup/original/3X/0/a/0ada0a86c3cfe209a41d75b089d3a694575174ad.jpeg)
While a ‘carpenters eye’ might be sufficient for building a house, the ‘coopers’ eyes needed to be much more accurate and they also would need a strict plan by marking all staves otherwise, his plan would fall apart (‘het plan viel in duigen’, the saying goes)
Planer:
Rounding of the bottom or top:
The nodges where also milled when the staves are being held together by ropes:
Feel free to pay a visit when things get a little more easier: