Borrmaskinen är högljudd, så vi använder borrmaskinen bara på dagen.

Because Swedish usually puts the definite article at the end of the noun.

• en borrmaskin = a drill
• borrmaskinen = the drill

So -en here means the.

This is very common in Swedish:

• en bil → bilen = the car
• en bok → boken = the book

Since borrmaskin is an en-word, its definite singular form is borrmaskinen.

You absolutely could say den:

• Borrmaskinen är högljudd, så vi använder den bara på dagen.

That is very natural and often more idiomatic in everyday Swedish.

Repeating borrmaskinen is not wrong, though. It can sound a bit more explicit or slightly heavier, but it is still grammatical. Learners often see repeated nouns in example sentences because they are clearer.

So:

• ...vi använder borrmaskinen... = correct
• ...vi använder den... = also correct, and often more natural in conversation

Är is the present tense of vara, which means to be.

• vara = to be
• är = is / am / are

So:

• Borrmaskinen är högljudd = The drill is loud

Swedish uses är for all persons in the present tense:

• jag är = I am
• du är = you are
• han/hon/den är = he/she/it is
• vi är = we are

Unlike English, the form does not change.

Adjectives in Swedish change form depending on the noun they describe.

Here, borrmaskinen is:

• singular
• common gender (en-word)
• definite

After är, Swedish often uses the adjective form that matches the noun’s gender/number pattern. For a singular common-gender noun, högljudd is the expected form.

Compare:

• en borrmaskin är högljudd = a drill is loud
• ett ljud är högljutt = a sound is loud
• borrmaskinerna är högljudda = the drills are loud

So högljudd matches borrmaskinen.

Because så here works like a coordinating connector meaning so, and the clause after it keeps normal main-clause word order.

Normal Swedish main-clause word order is:

• subject + verb
• vi använder

So:

• Borrmaskinen är högljudd, så vi använder borrmaskinen bara på dagen.

This is correct.

If some other element were placed first in the second clause, then the verb would come next because of Swedish V2 word order:

• ...så på dagen använder vi borrmaskinen.

But after så in this sentence, vi använder is the normal pattern.

Bara means only / just, and here it limits the time expression:

• bara på dagen = only during the day

So the sentence means the drill is used only in the daytime, not at night.

This placement is natural because bara is directly connected to what it limits.

Compare:

• vi använder borrmaskinen bara på dagen = we use the drill only during the day
• vi bara använder borrmaskinen på dagen can sound like we just use the drill during the day, with a slightly different focus

So in your sentence, bara på dagen is the clearest way to express the time restriction.

På dagen means during the day / in the daytime.

In this sentence, it contrasts with using the drill at night, so it means something like:

• only during daytime hours

This is a natural expression, but Swedish also has other similar time phrases:

• på dagen = in the daytime
• under dagen = during the day
• om dagen = by day / during the day, often in more formal or fixed expressions

In everyday Swedish, på dagen works well here.

Yes. That is often a more natural everyday version:

• Borrmaskinen är högljudd, så vi använder den bara på dagen.

Using den avoids repeating the noun. Swedish, like English, often prefers a pronoun once the thing has already been mentioned.

So the original sentence is good for learning and perfectly correct, but the pronoun version may sound more natural in ordinary speech.

The comma separates two main clauses:

• Borrmaskinen är högljudd
• så vi använder borrmaskinen bara på dagen

In Swedish, commas are sometimes used a bit less strictly than in English, but this comma is very normal and helps readability.

So:

• Borrmaskinen är högljudd, så vi använder den bara på dagen.

looks natural and clear.

The base form is använda, which means to use.

• att använda = to use
• använder = use / uses / are using, depending on context

In the sentence:

• vi använder = we use

Swedish present tense is simple compared with English because the verb form does not change for different subjects:

• jag använder
• du använder
• vi använder

all use the same present-tense form.

It is an en-word:

• en borrmaskin

That matters because it affects:

1. the definite form

   • borrmaskinen = the drill

2. pronouns

   • you refer back to it with den, not det

3. adjective agreement in some contexts

So you would say:

• Borrmaskinen är högljudd. Den är dyr.

not:

• Det är dyr when referring specifically to the drill as a noun

Yes, and this is a useful comparison.

Before the noun:

• en högljudd borrmaskin = a loud drill

After är:

• borrmaskinen är högljudd = the drill is loud

In both of these, högljudd matches a singular common-gender noun.

But if the noun were an ett-word, you would often get -t:

• ett högljutt ljud = a loud sound
• ljudet är högljutt = the sound is loud

So adjective endings are an important part of Swedish grammar.