Toward the end of Isaiah 28 several agricultural illustrations are used. Notice the references to the threshing sledge in verses 27 and 28.
Dill is not threshed with a threshing sledge, nor is a cart wheel rolled over cumin, but dill is beaten out with a stick, and cumin with a rod. Does one crush grain for bread? No, he does not thresh it forever; when he drives his cart wheel over it with his horses, he does not crush it. (Isaiah 28:27-28 ESV)
A threshing sledge was made of wood with sharp stones placed in the bottom. The sledge was pulled around and around over stalks of wheat or barley to cut the stalks into small pieces. The sledge was pulled by oxen or another animal. A young man, with perhaps some weights would be placed on top of the sledge to make it more efficient. The photo below shows an antique threshing sledge at Aphrodisias, Turkey.
The next photo shows another sledge with many of the stones still in place. Every time the sledge went over the grain the pieces became smaller.
The entire process of threshing, winnowing, and sifting, is shown in the art by Balage at Archaeology Illustrated.