Why half whole wheat is the right ceiling here
Garganelli are rolled twice: once by the pin, once around the dowel. Two rollings on a 100% whole wheat sheet will crack it along the bran lines. At 50% whole wheat against 50% 00 there is still enough extensibility to survive the second rolling, and the bran still gives the noodle a visible speckle and a nutty edge.
The rest is 40 minutes, longer than a plain 00 dough, because bran takes that long to hydrate fully. Under-rested whole wheat dough cracks at the dowel stage, not at the roller.
Cutting squares on the diagonal
Cut the sheet into 40 mm squares with a wheel. Work on the diagonal across the sheet rather than in a grid, so that every square has at least two edges that are already straight from the sheet's edge.
Keep the squares in a single layer under a cloth. Stacked, they weld; at 2.0 mm and 50% whole wheat, they weld within two minutes.
The comb, and what it actually does
A garganelli comb is a wooden board with 5 mm grooves. Lay a square over the dowel, press the leading edge down with your thumb, and roll the dowel away from you so the square wraps and the comb presses ridges into the outer face.
The ridges are not decoration. They triple the surface area of the finished piece, which is why garganelli can carry a meat ragù that would slide straight off a smooth tube of the same size. If you have no comb, the back of a wide-toothed wooden fork works, with a coarser ridge.
Drying and cooking
Dry 12 hours on a cloth-lined tray, seam side down so the tube does not unroll. Garganelli hold their shape better than any other hand-formed shape here because the ridges lock the roll.
Cook 7 minutes. The doubled wall of a rolled garganello takes longer than a flat noodle of the same thickness, and the hollow centre stays cooler than the outside.