1. Cut your sandpaper to size (250x90 mm). 2. Fold the edge 15mm inwards and hammer it down until you see the backing paper on the edge (you can also scrape the abrasive away on the edge). 3. Use superglue (ca glue) and spread it evenly across the entire fold. 4. Glue it to a sacrificial piece of wood and let it cure for at least 30 min. Separate the abrasive from the backing paper (you may need to experiment with different brands and types as this separation steps works better on some types than other). 5. Glue the sandpaper into a roll. 6. Round over the front and back edges of the body of the sanding block. 6. Test fit. 7. Cut the body piece in half. 8. Cut the wedge from a wider piece of plywood and at an angle of 5°. 9. Cut the edge of the wider piece of the body at an angle of 5°. 10. Insert the outer body pieces in the sandpaper rol and then in the middle gap push in the wedge until the sandpaper is tight (Don't over do it as you risk breaking the glue bond). Enjoy your sanding :)

Build video link: https://youtube.com/shorts/UvUGcNtR6Z4