the blank is 50mm X 230mm
ok so after i discovered a warp in my steel i had to cut 5mm off it to get one flat side

chopper builders handbook bender
then i centred and drilled it out to 25mm

chopper builders handbook bender
then i used the live centre to set the tool tip out to 3 inch (yes i do mix my measurements) and scribe a mark for the drive pivot holes

chopper builders handbook bender
next step is to mark and drill pivot holes and then turn the 32mm semi-circle onto the outer edge
good fun