It was intended to be broad :) Followup questions:
1. How does one produce a prototype? e.g. if you're in need for some custom part - do you contact to some manufacturer/factory, provide them some CAD files, etc... ?
2. Same question if you decide to produce a batch - where/how do you approach manufacturers/factories?
Also, how to make sure you are not going to be ripped off - e.g. those manufacturers can just produce your product and sell by themselves?
> do you contact to some manufacturer/factory, provide them some CAD files, etc... ?
Yes.
There are a wide variety of shops, and I am just talking here about proto-typing.
If you just want some metal tool plate precisely cut/drilled/tapped to specification (CAD drawings), there's a bunch of shops that specialize in prototype runs. I've used emachineshop.com, it was super easy and the results were exactly to spec. I like to design assemblies with such custom plates using 8020 extruded channels (8020.net) that can be ordered in cut/tapped sizes. Usually overkill and not appropriate for a finished product, it's heavy and expensive, but very customizable and robust. Perfect for few-of-a-kind builds or system-integration work.
The same thing goes for sheet metal fabrication and front panels. There's frontpanelexpress.com, they make front panels precision cut/finish and with whatever graphics you want.
1. Yes. There are lots of places that specialize in prototype level parts.
2. Your prototype vendor will be your small batch vendor too.
As for protecting yourself. Any prototype house worth anything should be willing to sign a non-disclosure agreement. They aren't in the business of ripping off their customers. That is a good way to kill their core business and spend a lot in legal fees.
Now, is your custome part a mechanical part or electrical like an IC? Your product is likely to made up of a bunch of off the shelf parts with a tiny bit of your "secret sauce". The secret sauce could be mechanical, electrical, software or some combination. Your goal at first is to prove out that part. Often this is done using develepment boards all cludged together to something that looks nothing like the final product, but demonstrates the concept. Then it is the next step to create more custom parts (PCBs, 3D printed case, etc.) so it can be prototyped in something closer to its final form.
I don't think you should be thinking about factories just yet. There is an ecosystem around startup hardware makers.
For custom parts, you can order 3D printing shops, or better, buy a 3D printing machine if you have the money.
For parts that are metal, get a machinist, or get the machines yourself if you plan on rapidly iterating (manual mill/lathe machines could do most thing. CNC if you could afford it).
If you make electronics, there are plenty of PCB prototyping services nowadays, where you send in a design and get a few boards to test.
A good side effect of doing it this way is you have total control and ownership of your product, no single factory owns your whole production line. And you don't need to order 10,000 for them to pick up the phone.
I'm a software engineer but have always been interested on how to make physical stuff, and I tinker with Arduino, Raspi etc projects regularly. Just my 2 cents.
1. How does one produce a prototype? e.g. if you're in need for some custom part - do you contact to some manufacturer/factory, provide them some CAD files, etc... ?
2. Same question if you decide to produce a batch - where/how do you approach manufacturers/factories?
Also, how to make sure you are not going to be ripped off - e.g. those manufacturers can just produce your product and sell by themselves?