Is needed a special equipment for cleaning 4 holes from a product filled with coke. Distance between them is always the same. Depth is 43 inches. Hardness of the product is 27 HRC. During the fabrication processes, the holes is filled with coke, which is needed to be removed. I'm thinking about at 4 end mill cutters mounted onto a structure which can allow to act simultaneously. Right now this job is a time consumer - around 10 min for each product - and is done using a hammer drill. Do you think ultrasonic waves could be a solution?