I didn't say that my workshop was idle. I said that consumption of iron for Mechanical Parts, wasn't worth the trade for coin.
Every two days my workshop produces 7 batches of fuel, & 35 batches block from 5,800 units of oil, & 34,200 units of cement. Ok, mabe I'm processing about 30 batches of block, because I not pulling all the cement out of the factory fast enough. (replenish time gets in the way)
The first task of every day is to pull all of the oil with one ship from the oil field. To make sure that I can do this, I make it a point not to leave my warehouse overstocked in the evening.