holes on suction conduct

[Emc2]

I have to realize the design of a relief made of a fume extraction conduct . the conduct in a straight section of about 6 meters has 12 holes with flanges dn 125 (measurements) and vents from 2" and 1/2" for temperature meters , anenometers pitot, etc., the holes are arranged staggered between them and with various angles regarding a passing plan for the center of the pipe. to realize the holes I find no other solution than to create planes in correspondence of the angle subdued from each single hole than the xy plane (plan more axis) and then project the plan in a sketch and create the point for the hole to the distance y regarding the connection flange of the conduct. does not exist a more practical system to locate a hole on curved surfaces without developing sheet?

greetings
robe

 

[Matteo Cappelli dis.CAD]

Hi.
if possible, make a hole and then a polar series
or, give the command "explain", do the holes and then "refill"

 

[Emc2]

I would not like to use the sheet module besides I can not use the polar series because the holes are high from the flange and almost all different angles.
p.s. the conduct is circular