How many slots are available for each machine?

Is it a set number for each machine or do they vary?

All machines can have up to 9 slots each, and I think you always starts with 2 slots when you get a new machine.

I prefer to open up all the 9 slots on machines with low production times such as dairy, sugar mill, coffee kiosk, popcorn pot and keep the rest of the machines on 6 or 7 slots depending on their production times. The smelters is fine on 3 slots but 2 works justa s well! :)

Thanks for the info!