Sync line and fan distance help

Hello everyone,

Looking for some information regarding the sync lines and fan distance area in 5 axis machining. At the moment i'm using hyperMill for making compressor impeller and i'm getting problems when flank milling the surface of the blade. The transition from one side surface to edge surface almost always leaves the mark on surface. Some times it's only "cosmetic" but more often the mark leaves impeller unusable. I'm able to set the fan distance area for flank mill operation, but i can't find the way to predict if it's going to be ok or not. Setting fan distance equal or a bit bigger then tool diameter helps, but often i have to modify surface of blade by cutting it into several smaller ones and go thought "try>error>try again until good" way.

So basically i'm looking for info about setting the fan distance, or making surfaces of the model right so i wouldn't need fan distance.
Pointing to right direction where to look for such information would help a lot.

Thanks in advance <label for="rb_iconid_7">http://www.cnczone.com/forums/images/icons/icon7.png</label>

In case someone will look for solution to similar problem.

Found the way to fix my problem. Now i just check generated NC code and look for the transition of on side surface to edge surface. If the problem is going to be the code has a small bug. I mean all five axes are moving and then one line in the code moves only XYZ but no other axes (B and C in my case) and the small line on the surface of finished part can be seen. So i just delete these lines and everything looks good then.