How accurate does my machine learning model need to be?
The accuracy level that should satisfy you depends on the reliability that your customer would have on it and the costs matrix of false predictions. 

He should put into consideration the costs of the unpredicted failures (low recall of your model) causing him production delays and the costs of over/false maintenance alarms (low precision of your model). If you know these costs you can minimize the expected cost equation which considers the precision recall and accuracy of your model: 

Expected cost
  = p(true positive) × "maintenance cost" 
  + p(false positive) × "inspection cost" 
  + p(true negative) × 0 (no action)
  + p(false negative) × "mechanical failure cost"