It all depends on context. Grammar is only a way of expressing meaning, so depending on the meaning you want to express, you choose the verb form. So :
Will expresses a prediction - a logical deduction. Whether it's past present or future is irrelevant. If you want to express a deduction, use
will. In this situation - Your husband is speaking on the phone. You say
" Sshh! You'll wake the baby!" he replies :
"Don't worry, I'm only speaking softly. I won't wake him." (This is logical deduction based on your belief that a) noise wakes sleeping people up b) the baby is asleep. Therefore your husband's conversation will wake him. Your husband's logic on the other hand is : a) There has to be a certain volume of noise before someone wakes up b) I'm not making that much noise. Therefore I won't wake him. Whether it's present or future is immaterial.
Will doesn't express time but the concept of logical deduction.
Now consider a second situation : the baby is asleep in his cot and you're cleaning his bedroom. You start talking to your husband and the baby starts turning over restlessly in his sleep. Your husband could say :
Let's go into the other room. We're waking the baby. or
Let's go into the other room or we'll wake the baby. In the first case he sees it as an on-going temporary event - already started and currently in progress, though with a predictable end - and so chooses the form (present continuous) which expresses that meaning. In the second, he's again making a prediction - with the same logical reasoning as before. You could then reply :
Don't worry - I'm speaking softly (again seeing it as an on-going event) or you could use will with its second meaning (volition) to make a spontaneous decision :
OK I'll speak more softly.
For a more detailed explanation of
will look back a couple of pages in this forum and you'll find a thread started by Michèle on
will and
going to. It's explained in detail there. And/Or look at this article :
Understanding Will
But in deciding which verb form to use, always keep in mind that it is context and intended meaning which determines the choice. decide what you want to "mean" and then use the verb which expresses that meaning.