Shaving with a machine gently after 3 weeks FUE transplant. I'm afraid I have caused damage

Only time will tell the result of a hair transplant surgery.  This will take 6 to 12 months.  However, shaving should not affect the result of a hair transplant surgery especially after 3 weeks.  Transplanted hair do not grow until 6 to 12 MONTHS in general. 

3 weeks post op, its fairly safe to shave. Transplanted hair does not grow immediately; first it goes into resting phase then starts growing 2-3 months post op. You should not worry if it doesnt grow back now.

Hi alon30What you are describing is the normal post op process underway. The hairs that were transplanted will stop growing fall out and three months later come up again. Any hairs that were originally there (so called existing hair) will grow after shaving. Most of the time transplanted hairs don't grow much.Check with your surgeon if you have concerns and to review the full post op course. But everything stated is indeed expected. Good luck. 

Normally you should be ok to do whatever you need to do if it has been over 10 days from the procedure date.

As you clearly stated, the scalp was free of crusts and you shaved the area gently. I would doubt that you did damage to your recipient area with that in mind. The grafts, once the crusts are gone, are secure and gentle shaving it is not a problem.