making money from 3d printing?

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IanJohnson, again, it is cool that you can use 3d printed parts for some equipment you sell, like jimc. But you make it sound like parts for professional or hobbyist equipment is the only thing that are made of plastic and can be sold. At this point im just repeating myself. Sure, for those kind of stuff the finishing of the plastic might not be a worry for the buyer, but everything else which you can make with plastic (and btw you're not really limited to plastic because you can make molds) is something which needs to look good (as in smooth and high res), doesn't it? If not, please tell me what aren't. because that's why I started this thread.
But please don't give another example of using a 3d printer for an existing job. I already understand that's a good option, but if you have a job like that where you could make use of your 3d printer.