I want to make a custom dock, but I do not know where to start and I have a few questions. I did find other people who had already done this, but they were from a long time ago and didn't include any info. I am also planning on 3d printing the case.
First of all, I heard that the contacts can just be connect to a spliced usb cable. If that is tru, then which side is + or - or how would I figure it out. Additinaly, what is the best way to get a good connection with the contacts? I'm open to buying whatever if it would work well.
Any help is appreciated, thanks!

Like you want to make a dock to hold and charge it?

Yes, exactly.

That sounds like a good project! When looking at the back of the calculator, the positive contact is on the right side. You can just splice a USB cable like you said.

If you want to 3d print it then you'll need to start by taking some measurements of the calculator. You'll use some CAD or 3d modeling software to create an object that will accommodate those dimensions.

Pretty sure OnShape is still free. I personally use Microsoft 3D builder but I wouldn't necessarily recommend it unless it's your only option. It's easy to get started but it's not super stable and projects are very difficult adjust if you make a mistake.

Ok, thanks! What would you suggest for getting good contact with the contacts while its in the dock?

You'll have to experiment with different things. Depending how you design it, you can probably get away with anything conductive like springs, bare wire, or even paperclips.

This post actually inspired me to have a go at this, and so far, a spade connector (with a bit of trimming on the side) seems to fit the best. You'll need something to keep the spade connector in the little indent, though. Good luck!

Do you have any photographs of the result that you can share, korbosoft?

It's absolutely not finished yet, but I can share the all the hacky wiring i've put together. https://imgur.com/a/aLUJkkE

It looks like an effective proof-of-concept! Do you have access to a 3D printer or a milling machine to make the dock itself? If not, I've had fairly good luck recently with overseas 3D printer services; for example, since I use JLCPCB for PCBs, I got this gray shroud resin-printed and painted by their 3D printing arm:

I do have access to a 3D printer, but I feel it would be somewhat easier to modify a cheap plastic stand I have (came with my Wii U, no idea what it's purpose was (the gamepad already had it's own charging dock)