I'm making a drill guide a bit of plywood. Extremely handy tool for opening 90 degree holes. Also the cost is very low. After watching the video you can do according to your own drill guide.
Making Video :
Go to this video's Youtube page and make a comment.
5cm marking - cutting
for my drill - 48mm hole saw - (Width to fit your drill)
2x - 11cm cutting (M8)
6X - 36mm cutting (Øin 8mm, Øout 10mm metal)
3x 34cm (Øout 8mm metal)
3X - 6cm hardwood Ø 25mm - Drilling 8,5mm
54mm hole saw