I grew up in and around a machine shop and likely forgot as much as I know. I was drilling holes for brass gauge stock on a drillpress much of my last preschool summer.
Regardless, I never skipped looking up at my charts when it matters a lot. (metallurgy, speeds, temps, bits, conversions, pressures, weights + books for what wasn't hanging up)
I can rattle off part numbers, bits etc, but I always check myself there too.
The rest is skill aquired, born to, or longed for.
There are days I considered going to a class for things, just because I might learn something new. (E.g. I knew hvac well enough to pass the general tests easily, but wanted to know more about some of the math and theory, so took the classes twice more, even after passing it the first time. (it was cheap and I attended casually )
I also took some blueprint reading "I didn't need" and picked up some things I missed while progressing to architectural drafting IV and having the HS #V & #VI dropped decades earlier. (Graphics and general drafting and woods was all that was left by my Sr. year. Autos, welding, metals, etc. were jokes by 1980 and gone soon after. Graphics, woods, and drafting seniors were at our 7th grade Jr high levels by 90 (now 6th thru 12th, no jr high seperation to mature in... just crankin out immature dummies that cant do simple math or print well with a pencil let alone write cursively, by the literal hundreds yearly now.)
Take a class?... Yep, you'll have fun because you want this 
