Querns can be automated by Mechanisms. To automate a quern, craft a Rind from Wrought Iron on an Tier-3 Anvil. Place the Rind in the handstone slot of the Quern. Next, craft and place a Millstone on the top of the quern by right-clicking. Attach the Millstone to a powered axle to power it. The quern will now automatically grind items that are placed in it. Hoppers placed under a quern will not remove items until either grinding stops, or when there is a full-stack of items in the quern's output slot.