Make sure that the knife is attached correctly. I.e. the blade of the knife must face outward, towards the disc. If you do a lot of mincing, the knife may need sharpening. Use a whetstone to do this. If the knife is very worn, it may be worth replacing it with a new knife. Sometimes, the piece of meat being minced may be the cause of the problem – it may contain a lot of sinews, perhaps. In such cases, begin with a coarser disc (8 mm), and then put the mince through increasingly finer discs. Finish off by mincing a bit of crust, a potato or a piece of onion, to clear the remaining meat from the mincer.