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A few quick questions regarding ～ておく and the casual form ～とく

Firstly, when changing from ～ておく to the more casual ～とく I'm assuming the verb
is first conjugated to the ～て form then the ～て is dropped and replaced with とく
and it can then be conjugated following the godan conjugation pattern as in
the examples below.

I.e.

> 勉強して → 勉強しておく → 勉強しとく

～とく conjugates as godan such that 勉強しときます and 勉強しときました. In the case of verbs
that have a ～で ending do they conjugate as どく？

I.e.

> 読んで → 読んでおく → 読んどく

～どく also conjugates as godan such that 読んどきます and 読んどきました

Is my understanding correct here?

Also, are there any nuances that make it outright different from ～つもりです in
terms of preparing for something? Is it simply that one of the sentences below
feels more natural than the other?

For example

> 明日試験があるので今晩勉強しておきます  
>  vs  
>  明日試験があるので今晩勉強するつもりです
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grammar verbs conjugations subsidiary-verbs
～ておく or ～とく for preparation (conjugation and nuance)
Yes, all your assumptions about about the conjugations are correct.

And far as comparing it to つもり, つもり simply means "intention (to do
something)". It doesn't directly have anything to do with preparation or doing
something beforehand. That it carries this mean in your example is incidental.
With your 勉強しておく sentence, the preparation is explicit; with the 勉強するつもり
sentence, the preparation is implicit. But in general, using つもり is not for
preparatory situations.

>   * 昨晩雪がたくさん降ったので、週末にスキーに行くつもりです → It snowed a lot last night, so I intend
> to go skiing this weekend.
>
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answer
When you contract `te oku` to `t'oku`, you're still conjugating `oku`, so the
normal rules apply. The only reason this might not be clear is that kana
prevents us from dividing `t'oku` into `t'` and `oku`.

Subsidiary verbs following ～て are
[grammaticalized](http://en.wikipedia.org/wiki/Grammaticalization), and people
tend to contract grammatical words. So naturally, there are a number of
contractions of ～て with subsidiary verbs you'll need to recognize, and each
one needs to be memorized individually. Some of them only appear in certain
dialects (or appear more often in specific dialects):

![table as image because tables are unsupported on Stack
Exchange](https://i.stack.imgur.com/ffAw7.png)

uncontracted | contracted | uncontracted | contracted  
---|---|---|---  
〜 **てい** る | 〜 **て** る | - **te i** ru | - **te'** ru  
〜 **てい** く | 〜 **て** く | - **te i** ku | - **te'** ku  
〜 **てお** く | 〜 **と** く | - **te o** ku | - **t'o** ku  
〜 **てお** る | 〜 **と** る | - **te o** ru | - **t'o** ru  
〜 **てしま** う | 〜 **ちま** う  
〜 **ちゃ** う | - **te sima** u | - **t'ima** u  
- **t'ya** u  
〜 **てい** らっしゃる | 〜 **て** らっしゃる | - **te i** rassyaru | - **te'** rassyaru  
〜 **てあ** る | 〜 **た** る | - **te a** ru | - **t'a** ru  
〜 **てや** る | 〜 **た** る | - **te ya** ru | - **t'a** ru  
〜 **てあ** げる | 〜 **た** げる | - **te a** geru | - **t'a** geru  
  
All of these have corresponding voiced versions when they contract with ～て's
voiced allomorph ～で, which in the case of ～ちまう・～ちゃう gives us ～じまう・～じゃう.

Of course, there are more contractions I haven't listed here, and I couldn't
begin to describe the range of dialectal variation out there, but I think
these are the main ones I've run into as a learner of Japanese.
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answer
It might help to think about what's going on with 「ておく」 and 「とく」 in romaji.

```

    " 勉強 shiteoku "
    
```

The we just drop the 'e' ('cause we're cool kids)...

```

    " 勉強 shitoku "
    
```

The same kind of thing happens all the time with 「い」"i"

```

    「何食べている？」 becomes 「何たべてる？」 (just drop the 「い」)
    "Nani tabeteiru?" becomes "Nani tabeteru?" (Just drop the 'i')
    
```

This can seem more confusing when it's written in kana because kana generally
represent a unique combination of consonant + vowel.

I have seen romaji used this way in junior high school and elementary school
to explain the finer points of Japanese verb conjugation to students.
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answer