Zımpara kâğıdı budağın çevresindeki yüzeyi düzeltti.

No. In zımpara kâğıdı, the -ı is not the accusative.

This is a very common Turkish noun compound:

• zımpara = sandpaper / sanding
• kâğıt = paper
• zımpara kâğıdı = sandpaper

In this kind of compound, the second noun often takes a 3rd-person possessive ending:

• kâğıt → kâğıdı

So zımpara kâğıdı is just the normal dictionary-style form of the compound, even when it is the subject.

If it were accusative, you would expect an extra case ending on the whole compound, such as zımpara kâğıdını.

There are two main clues:

1. Word order
   Turkish normally uses Subject + Object + Verb.
   So this sentence naturally reads:

• Zımpara kâğıdı = subject
• budağın çevresindeki yüzeyi = object
• düzeltti = verb

2. Case marking
   yüzeyi has the accusative ending -i, which marks it as the definite direct object.

So the structure is:

• The sandpaper
• smoothed the surface around the knot

Even though both kâğıdı and yüzeyi end in a vowel + -ı/-i, they are not the same kind of ending.

Because it is in the genitive case, meaning of the knot or the knot’s.

• budak = knot
• budağın = of the knot / the knot’s

This is part of a possessive-style construction:

• budağın çevresi = the knot’s surroundings / the area around the knot

Turkish often expresses relationships like this with:

• possessor in the genitive
• possessed noun with a possessive ending

So:

• budak → budağın
• çevre → çevresi

It is built from several parts:

• çevre = surroundings, area around
• çevresi = its surroundings / the surroundings of it
• çevresinde = in/at its surroundings
• çevresindeki = the one that is in/at its surroundings

So in this sentence:

• budağın çevresindeki yüzey = the surface that is around the knot

A more detailed breakdown is:

• çevre = surrounding area
• -si = possessive ending
• -nde = locative, meaning in/on/at
• -ki = turns the phrase into something adjectival, like the one that is ...

So çevresindeki functions like an adjective modifying yüzeyi.

Here -ki turns a location phrase into something that can describe a noun.

Compare:

• evde = in the house
• evdeki kitap = the book in the house

Similarly:

• çevresinde = in/around its surroundings
• çevresindeki yüzey = the surface that is around it

So -ki is very often used to make a phrase act like the one in/on/at... or the ... that is in/on/at...

In this sentence, it helps create:

• budağın çevresindeki yüzey = the surface around the knot

Because it is the definite direct object.

• yüzey = surface
• yüzeyi = the surface

Turkish typically marks a direct object with the accusative when it is specific/definite.

So:

• yüzey = a surface / surface in a general sense
• yüzeyi = the surface, a particular surface

Here the surface is clearly identified by the phrase budağın çevresindeki, so the accusative is exactly what you would expect.

Here düzeltti means something like smoothed, leveled, or made even.

It comes from düzeltmek, which means to straighten, to correct, to make smooth/even, depending on context.

Breakdown:

• düzelt- = verb stem
• -ti = past tense, third person singular

So:

• düzeltti = he/she/it corrected / straightened / smoothed

In this sentence, because the subject is sandpaper, the most natural meaning is smoothed or made even.

Because that is the normal Turkish sentence pattern.

A basic Turkish statement is usually:

• Subject + Object + Verb

So this sentence follows the standard order:

• Zımpara kâğıdı
• budağın çevresindeki yüzeyi
• düzeltti

English speakers often expect the verb earlier, but Turkish strongly prefers it at the end in neutral statements.

Other orders are possible for emphasis, but this version is the most straightforward.

Turkish ğ is usually not pronounced like a hard consonant such as English g.

Very often, it:

• lengthens the vowel before it, or
• creates a slight glide between vowels

So:

• budağın sounds roughly like buda-ın with a smooth transition
• kâğıdı sounds roughly like kaa-dı or kaa-ıdı, depending on speech style

The exact effect varies a little by word and speaker, but the key point is:

• ğ is usually soft and subtle
• it does not sound like English g in go

The circumflex in kâğıt / kâğıdı helps show a special pronunciation feature.

In words like this, it can indicate:

• a slightly longer vowel, and/or
• a palatalized consonant before it

For learners, the most useful practical point is this:

• kâğıt is pronounced differently from a simple kagit
• the â helps signal that the word has a more careful, traditional spelling and pronunciation

In everyday typing, some people may omit the circumflex, but you should recognize kâğıt as the standard form.

Yes, and that is a very good way to read it.

The whole phrase is:

• budağın çevresindeki yüzeyi

Its head noun is:

• yüzey = surface

Everything before it describes which surface:

• budağın = of the knot
• çevresindeki = around it / located around it

So the full phrase means:

• the surface around the knot

This is very common in Turkish: a long descriptive phrase comes before the main noun, and then the verb comes at the end.