finder file search results are irregular

If you don't want to deal with the "quirks" of spotlight then try something like Find any File.

I did quote the word "quirks", and yes, I was trying to be "nice". 😉

When you do a finder find (command F), search by filename (not "search for"), in your various examples, did you also specify the qualification "contains", or "begins with", etc. as appropriate?

Frankly, for general searches I use spotlight, but if I need a "real" serious search tool I use File Buddy, But because that is no longer supported I simply recommend Find any File instead. Easyfind is another alternative.

Blueberry Steve wrote:

I have been able to find/not find files depending on the portion of the file name I enter.

it seems to find the file if the search string starts with either the first character of the filename, or the second, but none of the other remaining characters in the file name.

That's not quite what happens. When you do the default search by name, Spotlight finds what it considers to be a word. For instance, it will find "leaf_blower", but not "leafblower" or "Hornblower". That's how the index was created, so that's what it finds. (If there is a reference which explains how the indexing service decides what in a file name is a word and what isn't, I haven't yet found it.)

To search for strings, rather than words, eg, to search for "blower" regardless of whether it's a word or not, you need to use the "Name" and "contains" criteria. If you don't see the Search Criteria bar, then either click the + button to the right of the Save button (if it's a - instead of a +, don't click it), or choose Show Search Criteria from the Action menu, ie

⚙

Then choose "Name" from the first pop-up menu and "contains" from the second (the latter is dynamic and changes depending on the selection in the first). I suspect your search results will conform closer to your expectations.

One tricky bit here. Make sure there's no string entered in the first Spotlight search box, the one with a magnifying glass icon. If there is, the "name contains" search will be performed only on the items found by the first search.

Now, don't ask why this behaviour isn't the default. I still miss the Find function in Panther; IMHO, Spotlight is a pathetic excuse for a search engine. If you want alternatives, in addition to Find Any File, I suggest EasyFind (which does a few different things from FAF) or John R Chang's Find File, which is a bit like FAF but very basic, with no options.