Just wondering how much is enough?
You typically do not not a hard helical twist. I use Bitzenburger fletching jigs and found that half to two thirds the possible helical available is more than adequate.
if you have a bitz and a helical clamp, set it up so you have the best mate possible between the fletch and the shaft and you will have all the helical you need in my oppinion and you will have feathers that stay attached as good as they get
I have a JoJan multifletcher and a Bohning jig. I set my jigs so my fletchings mate up the best with the shaft. Once you do this you will find with most jigs there will be plenty of helical.
What Old_Goat & James Kerr said.
I have a bitz and have done quite a bit of experimenting with twist on 4",5",5 1/2". Like most have said, the flattest glue line will last the longest as this is the clamp and jig design. I have found in most cases of a well tuned shaft you don't need that much helix as it slows the arrow down and creates more noise. I have went to a straight clamp and set the fletch to a good offset and have had very similar results with faster flight and less noise.
Well I'm using a Bitz. I have standard jig with left clamp and I get adequate twist but my buddy has a Left Jig with Left clamp and it seems he's getting crazy twist out of it.