Quenya has tanwë which means "device, craft, construction." A search for "machine" on this site which may or may not be reputable gives a couple of other words in Quenya, Sindarin, and Noldorin.
Tolkien did once use the word gun in the Hobbit. This question on sff explains that, and the top answer to it includes this quote:
The Common Speech, as the language of the Hobbits and their narratives, has inevitably been turned into modern English. In the process the difference between the varieties observable in the use of the Westron has been lessened. Some attempt has been made to represent these varieties by variations in the kind of English used ... (LOTR: The Return of the King, Appendix F, "II. On Translation")
I'd recommend reading the entire answer.
Anyway, it seems that, logically, there should be no words for "future" technologies in Middle earth; any translation of them by Tolkien can be explained as Tolkien trying to make it easier for us to understand.
The other point I want to bring up is that many of the words found in modern Quenya dictionaries are not original creations by Tolkien, but derivations from his notes. I doubt he created these words intentionally to violate the technology level of the world.
In the Black Speech, we have only a very limited number of words, as seen here; in Dwarvish, as you pointed out in your own answer here, Tolkien has a very limited vocabulary, and only one word has been borrowed from Khuzdul into the Elvish languages.
I think the quote you have about Sauron being a robot is not literal--the orcs' tehnology was no more advanced than the men and the elves'. I'm sure that "mind of metal and wheels" is meant to be some Entish idiom that references being hasty.
