Ich finde es leichter zu bohren, wenn die Bohrmaschine nicht so schwer ist.

Here es is a kind of placeholder object. German often uses es in patterns like:

• Ich finde es schwer, ...
• Ich finde es interessant, ...
• Ich finde es leichter, ...

It works a lot like English I find it easier to drill...

The real content comes in the zu + infinitive phrase: zu bohren. So structurally, the sentence is saying:

• I find it easier — what?
• to drill

So es does not refer to a specific thing like the drill; it is just part of the sentence pattern.

Because after expressions like es ist leicht, ich finde es schwer, es ist wichtig, German normally uses zu + infinitive.

So:

• leicht zu verstehen = easy to understand
• schwer zu machen = hard to do
• leichter zu bohren = easier to drill

This is very similar to English to drill.

A useful pattern to remember is:

• Ich finde es + adjective/comparative + zu + infinitive

Examples:

• Ich finde es schwer, Deutsch zu lernen.
• Ich finde es einfacher, früh anzufangen.

Leichter is the comparative form of leicht.

• leicht = easy / light
• leichter = easier / lighter

In this sentence, leichter means easier, not lighter. The meaning is determined by context.

So:

• Ich finde es leichter zu bohren = I find drilling easier

This is a common point because leicht can refer either to difficulty or to weight.

Because it is being used predicatively, not directly before a noun.

Compare:

• eine leichte Bohrmaschine = a light/easy drill machine

  • here leichte comes before a noun, so it takes an ending

• Die Bohrmaschine ist leicht = the drill is light

  • here leicht is after ist, so no ending

• Ich finde es leichter zu bohren

  • here leichter is also not before a noun, so no adjective ending

It is just the comparative form standing on its own.

Here it means heavy.

That is because schwer describes die Bohrmaschine, which is a physical object:

• wenn die Bohrmaschine nicht so schwer ist
  = if the drill isn’t so heavy

Just like leicht, schwer can also have two meanings:

• schwer = heavy
• schwer = difficult

Context tells you which one is meant.

In this sentence, there is a nice contrast:

• leichter = easier
• schwer = heavy

So the idea is: drilling is easier when the machine is not so heavy.

Wenn introduces a subordinate clause meaning if here.

So:

• wenn die Bohrmaschine nicht so schwer ist
  = if the drill is not so heavy

For learners, it helps to remember that wenn can often mean:

• if
• when (especially for repeated or general situations)

In this sentence, it is a condition, so if is the natural English equivalent.

Because wenn starts a subordinate clause, and in German subordinate clauses send the conjugated verb to the end.

Main clause:

• Ich finde es leichter zu bohren

Subordinate clause:

• wenn die Bohrmaschine nicht so schwer ist

That final ist is completely normal after wenn.

You will see the same thing with other subordinating conjunctions too:

• weil er müde ist
• dass sie kommt
• obwohl es regnet

Because German normally uses a comma before a subordinate clause.

Here the sentence has:

• main clause: Ich finde es leichter zu bohren
• subordinate clause: wenn die Bohrmaschine nicht so schwer ist

So the comma marks the boundary between them.

This is much more regular in German than in English, so it is worth getting used to.

Bohrmaschine is feminine, so it is die Bohrmaschine.

This is a compound noun:

• bohren = to drill
• Maschine = machine

In German compound nouns, the last part determines the gender. Since die Maschine is feminine, die Bohrmaschine is also feminine.

That is why the sentence says:

• die Bohrmaschine

The understood subject is usually the same as the subject of the main clause: ich.

So the natural interpretation is:

• Ich finde es leichter [für mich] zu bohren ...
• I find it easier [for me] to drill ...

German often leaves that subject unspoken in zu + infinitive constructions when it is clear from context.

Because the sentence is talking about the weight of the drill, not directly comparing two drills in a strict grammatical comparison.

• nicht so schwer = not so heavy
• leichter = lighter

Both are possible in some contexts, but they are not exactly the same.

nicht so schwer sounds a bit softer and more relative:

• the drill is not that heavy

leichter would sound more directly comparative:

• the drill is lighter

So nicht so schwer ist fits well if the speaker means that reduced weight makes drilling easier, without necessarily comparing it to one specific other drill.