Some espresso machines come with a lever to compact the ground coffee before the espresso starts the brewing, other machines do the compacting part by themselves.
How much leverage or pressure is it required to make the coffee compact enough to go to the next step of brewing the espresso, and what happens if I put too much pressure (i.e equivalent to 1ton)?
Based on your comment on the question, you are referring to compacting ground coffee in the portafilter. This process is referred to as tamping when making espresso.
The widely-accepted amount of downward force to use when tamping a standard double shot of espresso is 30 lbs. You can view a source here but if you simply do a google search for "espresso tamping pressure" you will see 30 lbs mentioned ubiquitously.
If you are using a tamper directly on the coffee grinds, it is easy to practice putting down 30 lbs of force by practicing on a scale. If you are indeed using a lever to do the tamping, I suggest reading the instructions that came with your machine.
30 lbs of force on the lever may not result in 30 lbs of force on the espresso, depending on the setup of your machine. The lever may even be engineered specifically to stop tamping at 30 lbs. Tamping espresso with a lever setup can be a bit of controversial thing in the coffee world.
Whatever your setup, you want 30 lbs of downward force to result from whatever it is that contacts with the ground coffee and tamps it down.
Putting too much force on the ground coffee is called over-tamping. The coffee grinds can become over-compacted which can slow down extraction (lead to over-extraction) of the espresso, lead to channeling (where water finds inconsistencies in the grind and channels through in small spots, leading to unequal extraction in the espresso puck), or even block it completely.
If you used 1 ton of downward force when tamping, I suggest that you will likely break your portafilter and its basket, along with whatever is beneath it.
