I designed a product over 10 years ago, never got it patented, a machine shop is making and selling it. They have not made any design or usage changes. Can they get a patent on it? Can I get a patent on it?
Great question. Neither you nor the machine shop can patent it. Once the invention enters the public domain, it is no longer eligible.
"...an invention cannot be patented if...the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention.
In the US, there is a one-year grace period from the time of public disclosure in which the inventor can file for a patent. Details as USPTO
Your best protection is to make sure the Intellectual Property is easy to find on the web, just in case someone decides to be sneaky and see if they can slip it by the review board. You may find these links useful: