UPDATE: According to few comments on my YT video guide, this farming method was patched out on 1.1.0 version of the game. I haven't tested this myself, but I will specify it regardless.

The Craftory (the shop in the game) offers a great selection of items to purchase. However, to buy all of them, you will have to farm for materials.

While there are some great farming spots, most of them require you to run around and destroy furniture and whatnot. And you see, I'm lazy. So I've set on a quest to find a way to farm materials without me actually participating in the game. And I've found it! In fact, it makes me materials even as I'm writing this guide.

Disclamer: this method of farming is focused on player not participating, and might not be as time-efficient as other farming methods. So far, the approximate rate of resource gain is around 50k materials per 30 minutes.

Additionally, this farming method was tested only on Normal difficulty, and might be harder to pull off on higher difficulties due to its nature.

Last tested game version - 1.0.4

So, if we are not going to break boxes, how we are going to get any materials? My idea relies on three simple aspects:

• You can gain materials while defeating the enemies.
  
• There are areas where enemies can spawn indefinitely.
  
• Some of your Homunculi can defeat enemies without your participation.

So, let's go over each of those points.

The very heart of our little farm. This relic allows you to obtain materials while defeating enemies. The chance is not very high, so it is not very good on its own, but for this method, it is perfect. Especially considering that it works on spawned enemies (at least at the time when this guide is being written). So effectively, we can just sit on the spot where enemies spawn, kill them, and keep getting materials.

Note: evidently, the relic also is capable of giving you scrap, but seemingly loses this capability when upgraded as of 1.0.4, relic effect is fixed, and upgraded version gives scrap as well (credit to @TW_Strange)

The relic itself can be found in Declan's Estate (credit to @The Jacobian)

So, what enemies we could be killing for this?

Yes, those rats. The bane of early game. Time for them to pay for what they did to you. Literally.
Those are spawned up to three per spawner device with pretty small delay, which means, you will effectively kill 1-2 rats each few seconds.

The other option would be the robots in the factory, but I'm honestly not sure how effective it would be. Especially considering that those robots also have ranged attacks.

And to the last piece of puzzle - how do we kill those rats.

Wave Beam is third ability of Lorna, which makes her emit wave pulses sideways. This is perfect against the rats - basically this creates pretty large horizonal "killbox" area which quickly kills any rats trying to reach you.

Gravity Well is Lorna's first ability, which also works quite well in some setups. It offers higher damage at cost of smaller area of damage.

Usually, when you use any Lorna skill, you "throw" her forward a little. But you can control her position almost precisely if you use her skill while holding "down" directional button or stick.

There are two locations with rats - Subterranean Waterway and Biological Research Facility. I've decided to settle in the second area. This would probably work in either, but I'm also not sure if early game location will actually give you decent materials amount (needs to be tested).
Here is exact location where I'm setting up the farm.


Particular spawner is picked because it allows to ensure that rats will not get too far from Lilac and deaggro.

So, when you have everything that is required, you can approach a rat spawner, put down Lorna, and just leave the game running. Luckily enough, the game keeps running even if you switch tabs, so you can even just switch to some other activity on your PC.
Important part is to pick proper position both for Lilac and for Lorna. Being too close will allow rats to survive few pulses and jump you, being too far may put some spawned rats outside of aggro range. Your perfect setup is when the enemies jump right into the area where the beam is the biggest.
Here is the position I've picked, and it works perfectly.


And a video to demonstrate how does it work.

Alternative location is to put Lilac on the wall left of the spawner - this will ensure you are not getting hit by rats, and most rats are killed by backing up from you. The only caveat here is that some rats will try to jump at you just into the wall, intead of jumping or running into the Lorna ability zone, which makes them live longer. I'm, however, not sure if this affects the rate of materials gain.

Few other things that could be considered for higher success rate:

The damage plays critical part here, as it is what doesn't allow rats to kill you. So focus on it when gathering your gear - pick your highest output bracelets, relics with bonus damage (especially House Milius Earings, which increase damage of autonomous skills, so it will affect Lorna), carapace that focuses stats. In my game, a singular tick of Wave Beam deals 163 damage to rats, and it is enough.

While proper positioning and high damage will ensure that the rats will not reach you most of the time, this will most likely happen occasionally, so you should pick healing relic as a contingency. Helix Crystal works incredibly well here, as you will kill enemies constantly.

Needless to say, if you can upgrade anything that participates in this farm - do it. Especially Headless Gold Relic - the increased chance of drops will increase average amount of materials you gain (but take into account that non-upgraded relic also has a chance to give you scrap, and upgraded relic does not, for some reason fixed in 1.0.4). And any damage upgrades will help you succeed.

This might be funny to mention, but if you are playing with wireless gamepad, and it automatically turns off, the game will show the message about gamepad disconnected. Which obviously can interrupt farming while you are away. So take care of that beforehand.

And that's it! Let me know in the comments if this guide has helped you, or if you have any suggestions. And if it did helped you - don't forget to like it so Steam considers it useful :D

Updates:

• Update #1: game update 1.0.3 - apparently Lorna was nerfed. Retested, the farm method still works, no changes in Wave Beam damage.
  
• Update #2: game update 1.0.4 - retested the method, still works. Also, upgraded Headless Gold Statue now gives you scrap, as it should. Additionally, added alternative option for the Lilac placement, as proposed by multiple people in the comments.

Credits:

• @Nyaqua, @Geeji, @Cantrp and @Bk-Mute - for safer placement option for Lilac.
  
• @The Jacobian - for pointing out Headless Gold Statue relative location.
  
• @TW_Strange - for clarifying that Headless Gold Statue is supposed to give scrap.