My friend Andrew Geeky devised this reusable centering system that needs no pegs or screws.
The wood bars slide out and the sides fold in at the bottom and the plywood semi circle supports drop down leaving the arch supporting itself . The wall at his house (top photo) has several niches in them which he made using these retractable forms. He kindly gave me two of them which I use at my workshops with kids to teach some of the basics of dry stone arch building
