Kentucky Energy (fka QMIN)

[kojak79]

Generally speaking, when a mine is performing a lot of rehab work, they'll have a machine to use just for rehab (usally a "beater", or one that already has a bunch of tons on it). Cutting down rock is a lot harder on the machine than cutting coal, so they won't want to put the better of the two into the rehav. They can also use the beater to load out roof falls, and in those areas, they'll need to re-bolt the top, which is where a good portion of those 30,000 roof bolt are used.
Once they're finished with rehad and are ready for production, they park the "rehab" machine, and put the good one in the coal. Thus the spare machine. If the rehab looks to be finished, they can bring the spare up to snuff, and have it ready to go into another production area, similar to what Cedar Grove will do.
Hope this has helped.