When upgrading mine patches to higher tier, I always found myself where I'm having a ridiculous amount unused lower tier miners. My suggestion is to use lower tier miner as an ingredient for higher tier miner, thus lower tier of miner is not wasted.

Yeah since the creation of the mod I wanted to create a thing like this, but didn't know if creating a sort of "Ev: recycling" mod or implement some normal recipes.

Because the thing is:
- When I want to upgrade mining outposts I need to upgrade the mining drills otherwise, as you're saying, I'll waste all them;
- BUT if I only want to create a new area, and so don't need to upgrade anything, all the "recursive" craftings (mk1 that becomes mk2 that becomes mk3...) aren't needed. Creating an ENTIRE setup only for crafting mining drills only to achieve the top tier that I need (like belts) seems to me overkill.

Expect to see an update regarding this argument these days, however.
_77Playmaker

Creating an ENTIRE setup only for crafting mining drills only to achieve the top tier that I need (like belts) seems to me overkill.

Fair point. Maybe the better option is, as you've suggested, a recycling mod (like this one: https://mods.factorio.com/mod/ZRecycling).

Version: 1.3.0
Date: 2020.10.11
Features:
- Now mining drills can be crafted in two different ways:
- Direct Crafting: Each mining drill has its own crafting that doesn't require the previous
ones (the old normal crafting);
- Recursive Crafting: The drills now have also an "upgrade" crafting that will allow you
to recycle your old drills once you'll research a new tier. No more drill waste.
- Upgrading a tier to another will be less expensive than directly craft the same drill,
but will take more time.

In the end, I've decided to take a sort of "middle ground": now it's up to you to decide how to craft these drills. :D
- You want to recycle? Sure, do it if you like to create big, cheaper setups;
- You want to achieve that tier faster and have not problems in spending more resources? Here you are.

Cool, now I could make a dedicated drills assembly line. Thanks!

Well have fun then :D

Wonderful, thanks 77Playmaker!

Thank you for the request: if you want to tell me something else do it and, if you want, you can enter in my discord server :D