I'm currently in my third year of undergraduate Physics, and plan to graduate at the end of my fifth year (since I'm doing CO-OP). I'm starting to think about grad schools, one element of which is my faculty recommendations. I worked in a well known scientist's lab in my first year, first summer, and then again in my second summer (this last one). I'm looking to try and make a good work-relationship with other faculty members at my school, but I'm wondering if after a couple years professors aren't likely to give old recommendations. By the time I apply to grad schools I will not have worked with this scientist for three years, is that still a common time frame to ask for a recommendation for grad school? I wouldn't want to make a fool of myself asking them if it isn't common, but I have no idea. I know that that they have a good opinion of me, and know that they would write me a strong recommendation. Anybody familiar with things like this? Thanks!