Slashed out 2x4 SPF wood in vertical 30 degree using a band saw or table saw. 5 bolts are set to vise a bamboo strip in between. Rubber belts inside will hold a strip to stay at the appropriate depth. Form length 150 cm, width 7cm, thickness 3.5cm
Vise-ing a strip tightly, then the strip will lean over 30 degree wall.
Slash out the outside portion of strip by using a big power. The picture is a Japanese style plane which has a big hard steel blade, which sole is grooved. You can use bench plane instead, or power plane. Power plane will not plane the form by setting the depth of the blade to the effect. 60 degree angle is automatically there.
A combination of wooden rough forms. Left: adjustable rough planing form Right: First Angle Form, SLASH Grooved sole plane could be another good idea to use with these wooden forms too, using a scarely sharpened hard steel blade.