Google recently removed a feature by which you could restrict your searches to forum discussions. It was under the "More" menu, alongside Maps, Books, Flights, Apps. There are some workarounds.
You can use inurl:forum, since many forums include "forum" in most of their urls. Most forums (not this one, because we paid a fee to remove it) include the name of the company that writes the forum software in the page footer. For example, some common ones are vBulletin, phpBB, and XenForo. And, the words in those company names are uncommon; they won't occur normally on other web pages. So, you add those brand names to your search. You can separate different words with the pipe character (often found above your return key on your keyboard) to indicate "or".
And of course we can enclose a phrase (like "disc sander") in double-quotes, to indicate that we're searching for the phrase "disc sander", and not the word "disc" and also the word "sander".
So, a sample search would look like this:
"disc sander" vbulletin|phpbb|xenforo
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