I usually begin to wean at about 6 weeks, and I separate them from momma then as well. I will take them out, and put them in separate cages, and bring them to momma every day, and then every other day, etc. etc. until soon they just don't go for milk.
With my past litter, I separated them at 8 weeks since they were on the smaller side, but when we went to put them back with Chancey, she wouldn't let them drink milk, so she pretty much weaned them by herself, and we haven't had to put them back with her.
I just separated my buck from his sissy, and he is quiet now, whereas he used to be hyper and an escape artist. He misses her, but he's the only buck in the litter, and was already beginning to mount her. His papa his right next to him though, and we gave him a toy for enrichment, so hopefully he'll get better.
Emily