can I move deep drills around randomly and hope to find something? (do I need to scan deep ore before I can mine)

[Combat Droid]

Title

[Narrowmind]

Sure. Chunks are everywhere.

[Yxklyx]

I would not move them around randomly - get that locating device, once you run out of the resource you located it can be useful to just get the chunks but probably better to move it right next to your stonecutter table.

[Minty Fresh]

No, the ground-penetrating scanner "generates" the ores that it finds. Drilling there before they are found by the scanner will just give you chunks.

[glass zebra]

Used to be like this, now the scanner generates the resources. The upside is that it means you get infinite renewability.

[Playzr 🐵]

In my opinion the usefulness of the scanner has been reduced to the point where you need to have a researcher who would otherwise be researching useful stuff, spends days just to find yet another tiny deposit, probably underneath something useful that you have to tear down to get to, then you have to have a miner stand next to the drill for days to get a bit more steel or whatever. If it's your only option then do that, but mods add better ways to solve your sudden steel and plasteel shortage. I liked it more when the map was already covered in deposits but you had to turn on your scanner long enough to find a spot to place the drills, and even more useful when they made it so you can move the drill instead of having to rebuild it. And there were those times where you turned it on for a moment to place a drill but forgot to turn it off and it drains your power overnight and a big raid comes when your turrets are out of juice.

[glass zebra]

The deposits by the mineral scanner are not to fix a sudden shortage, but provide a giant amount of metal. They are mostly for late game when you don't research anyway. This interferes with modded games that have a hundred more things to research than vanilla though.

[Playzr 🐵]

It's definitely fixed my sudden shortage, although I wouldn't say it was exclusively for that.

[Yxklyx]

You can reinstall the drill. The steel and plasteel sites are worth it IMHO. The others not really. I usually just build an independent building with one solar panel and one battery so I don't need to fudge with the power. The infestations that appear now can be viewed as an added bonus.

[Playzr 🐵]

You have scanned for 5 days. You have revealed an underground deposit of useless crap you already have too much of. Time to replay the long gamble again and hope for something useful. In the time it took to scan for that tiny deposit you could've just gone around digging holes randomly and found something more useful. It would even be more effective to walk around with a metal detector. When you do find the deposit you're looking for and have the man power to mine it for days it's worth it, but until then there are other ways you could've obtained that bit of steel. Need a load of steel? Already have a load of steel? Build a scanner and drill out of all that steel. Definitely takes some planning as you notice you're running low, maybe trade for just enough to build the stuff. I'd probably start using the scanners if they were automatic again, maybe you'd have to leave it running over time.

[Astasia]

This is just the game reminding you that you can have more than one researcher. Have two research benches and 3 colonists assigned to researching, one scans the others continue progress. If you want something specific you use the long range mineral scanner and pick what you want, if you just want general passive resource generation deep drilling provides a free endless supply without having to go anywhere, and the drills give your miners something to do after mining out everything on the map.

Deep drilling isn't about "I need X" so lets quickly drill for it. It's more, "I have nothing else to do so lets drill" and long term you end up tons of resources by just keeping your colonists from being idle.

[KPJFormat]

Intellectual is also a useful skill for various quests, best to have a way to use it other than just researching. Researching is well and good but there's only so much to do, and researching everything too quickly is a waste of labour too.

If you aren't short on steel or plasteel, you will be eventually. It gets further and further you must go to get it, having a mining drill right in your base can be an amazing source. Where does it all go? If not towards a space ship, then it is for turrets, armours, and bionic parts for your colonists.

As for the 'realism' immersion of it. You've got to get the drill to just the right depth, and place it so that it can drill through softer rock rather than harder. That's why it takes a lot of research and why you can't just plunk them down and guess.

[Playzr 🐵]

I reckon if you filled every tile of the map with drills (with a space for a worker to stand) and manned them all somehow there'd be too much rock to move let alone notice if any steel appeared. Also everybody would be sick of eating rock soup and sleeping on a drill.
My favourite solution to this problem is the automatic drills from Project Rimfactory. They can actually produce more steel than you'll ever need, but it's a significant amount of work to get to that point starting with the standard 3 colonists.