You don't get a 3D printer to save money. I have been 3D printing for a quite a few years now, FDM stuff. I have a cheapy clone, and it does work, and works well, but takes a lot of fiddling to get it right, and that is only for a short period of time, then it takes more fiddling. Around Sept of 2021, the hot end blew out ( the part that melts and squirts out the filament). A replacement was not going to be available until November, of 2023. So I ordered a Prusa Mini. All I can say is it was a little more money than the cheap one, but once setup, and that part is WAY easier than the cheap one I have, it is VERY consistent until I change filament to a different brand, or type. (PLA vs PETG) . Then about 5-10 minutes of setup, and it is good to go again until I change filament.
I have designed and printed all sorts of useful things; some that were not commercial available. I am an armature astronomer, and have designed adapters and various mounts for finders (Telrad specifically), and the "precision" is good enough for that.
Yes the surface finish can be a bit rough. I just recently got into this hobby, and plan on making some N-Scale bridges, and other Structure type things. I have been playing with layer height. Smaller layer height makes the seams between layers less visible, but take more time to print. It seems good enough for none forefront items. Or with some filler and primer, it may be a moot point.
I have also designed and printed point servo mounts with provisions to mount small lever switches and a drill jig to facilitate mounting under the layout. Super easy to install and everything is lined up on the first try.
So far the best thing I have printed for the RR is a tool to install rail joiners on N-scale track. No more pricked thumbs. They slide on perfectly 1/2 way with ease now.
Also designed and printed mounts for the various circuit boards I use and some wire clips.
Examples here.
4 new items added to shared album
photos.app.goo.gl
For designing the items, I use Fusion360, the free version. I have not found any limitations for my use with this limited version. It is fairly easy once you get the basics from a few youtube videos. If you have no CAD experience I hear TickerCAD is the way to get started.
So if this is something that interests you, by all means go for it. Will you save money? No. Will you have a chance to explore new creative outlets, and have some one-of items or be able to make something that you can't by. Defiantly.