Thought coolant concentration was a scam until an old timer on my shift proved me wrong with a refractometer
I used to just top off the sump with straight water whenever it got low and figured the mix ratio did not matter much on aluminum. Then a guy with 30 years on the floor showed me his refractometer reading 8% on our mill that I had been running at maybe 3%, and the tool life difference over one week on 6061 was real. Anybody here actually check their concentration every week or do you just dump and refill when it starts smelling?
Running straight water in aluminum is basically how you turn a nice finish into a fuzzy mess, so the old timer did you a solid. The funny part is the smell test crowd thinks a sump that reeks like a dead raccoon is still good to go, meanwhile the refrac reads 2% and the tools are crying. We check ours every Monday and log it on the machine, takes like 20 seconds and saves way more than it costs.