Originally Posted by fredmdbud
Was this your first run-up in the fixture? How fast did you increase the throttle?
Those plastic EDF shrouds are relatively easy to flex and deform. If you raise the throttle gradually, you will be able to detect if the blades are rubbing at a lower RPM. When mounting the unit, I suggest doing it with the lip ring installed as a brace to minimize the chance of the duct flexing.
You also do not need to go to full power to balance, just enough where vibration starts to happen, and then consistently return to that setting during the balancing process.
Just now getting back to this thread. This was the first run up. I increased the throttle slowly up to about half and then back down. Then slowly up to full and then back down. Then on the third try at about 3/4 throttle the fan blade flew off. What do you mean by "lip ring" ? Do you mean the entire foam ring the EDF sits in? There is a picture of my test rig on the "Balancing an EDF using a cell phone" thread. It's either the last page or second to last.