ok ive search and made a paper template and it works, well pretty dam close. this is the simple way to explain it
work out how big you want your dome and how many sections you want to make to form this dome.
for example
having a diameter of 100mm and lets make it from 4 sections.
100mm diameter has a circumference of 314mm.
314 divided by 4 is 78.5.
this means the width of each section is 78.5mm (natural more sections means more curve)
how to work out the height. The height is 1.5 times its width. so we have 78.5mm as our width. so thats means our height is 117.75mm
so on your paper, cardboard or whatever your using mark out your width, mark the height then using your compass make the lines radius. ill try get some pics up.
i am 90% sure this is right. and i will be trying this again on metal to see if its going to work out before i try it on the actuall job