Others have expressed themselves quite succinctly regarding the sagacity
of your instructor and I fully concur with them.

But let me add a short note on lung protection.

I have a shop-built air cleaner that I calculate (back of the lunch bag
numbers) filters my shop air roughly 3 times a minute. Yeah ... that's a
pretty noticeable breeze! I have a stack of three filters. The first is
a normal 79 cent furnace filter that grabs stuff that would have settled
out of the air if I weren't stirring it up so much. The second, a 5
micron filter, gets the air clean-looking ... that is, if it was the
final filter, I'd be fooled into thinking that my air was clean. The
third filter is rated to pass nothing bigger then 0.3 microns. Thats
smaller than dust. Smaller than bacteria. Smaller, even, than some viruses.

With that much air filtration, you'd think that dirty air would be the
least of my concerns, eh?

But I still wear a 1/2 mask respirator (~$26 at Harbor Freight) because
I am closer to where the dust is generated than the filter is ... so my
lungs get first dibs on it.

There is an older carpenter that I know. He provided well for his family
and retired with a workshop bigger than my house and yard combined. But
he never wore so much as a dust mask.

He's doing well to get 2 or 3 words out between coughs.

Lathe work generates a lot of dust to go with the shavings.
You do the math.

Bill

--
Political Correctness relies on the presumption that it is possible to
pick up a turd by the clean end. -- Me, 2006