Is there a reason why one's calfs would ache on a Turbo or Spinner, but not when riding on the road?
There are likely a few different reasons, but my primary suspicion would be fit. Presumably your road bike is set up to fit your body geometry and angles, where the spin bike is not. Small differences in how a bike is set up can have a big impact on how your body feels while riding.

My n=1 example, when doing higher intensity efforts on the road, I would get high calf cramps after about an hour. When I had a Retul fit done for my time trial bike, the fitter told me that because my feet were somewhat duckfooted, I needed to move to speedplay pedals with longer spindles to allow my heels to drift inward more than my old pedals. Solved my calf cramp problems.