lee, what model dremmel are you using ? the reason i ask is i have found, over the years, some models develop in/out play in the chuck shaft that can cause slips [goof ups] to occur. i'm not sure what model[s] those were, but i had to come up with some method to remove the clearances. it usually meant shimming the bearings as didn't want to take a chance with doing anything with the shaft, least creating any wobble. i wished i could remember the model number ! it may just have been a bad batch or two ? anyone else run into this problem ?