Chapter 2, Problem 30P

A company uses a variable speed honing machine to increase the smoothness of the inside walls of hydraulic jacks. The hone uses acid-dipped “brushes” to perform this operation. Increasing the speed of the machine results in faster operation, but reduces brush life. A single “brush” costs $90.00 and can be refurbished several times before its useful life is over. The number of refurbishings depends on the honing speed. Each refurbishing costs $30.00. Assume a refurbished brush can smooth the same amount as a new brush, and that when purchased a new brush is ready to use. The operating cost for the hone and operator is $70.00/hr. Below are the data for operating the hone at 3 different speeds. The time required for changing brushes is incorporated into the honing rates below. Which honing speed is the most economical? Hint: find the cost per jack, not per hone or per cycle!