The last 2 times i ground meat for sausage I noticed there is some unground meat and fat when I get done grinding. I always run some of the of the ground meat back through the grinder to push any meat out that is still in there. I noticed last night that there was some chunks of fat left i front of the blade when I was done grinding. Is my blade dull? Plate bad? When do you know you need to replace the blade or plates?