Lathe coolants?

If carbide inserts are continuously flooded, then there is no issue. If a very hot insert is then flooded, it can crack from the heat/cooling stresses. I am not sure if this is a common problem.
 
About your carbide inserts --- I've been told a number of times that coolants and carbide don't mix. Apparently the repeated heating/cooling as they work causes the carbide to crack or break down. Something to consider, maybe....
Whoever told you that carbide and coolants don't mix obviously didn't know what they were talking about. Now if they run the tool until it is really hot, then turn on the coolant, Yup could be a problem. But who the he!! would do that? My shop is in an Industrial area and I have been in many of the production/job shops. They all run coolant, even on the few manual machines that are still around.
 
Since you don't need coolant regularly, I would suggest a mist system. I'm not familiar with any coolants that will not go rancid over time, particularly if they are not circulated (oxygenated) regularly. Keeping a coolant system clean and functioning is enough of a pain when you DO need it. I don't miss coming home smelling of rancid coolant.
 
I use Castrol Syntilo. It doesn't smell, doesen't built up bacteria, no smoke, Mixes 40:1 with water and its clear, so you can see what your doing.
But coolants are like tooth paste, everyone has a favorite.
 
Another vote vote for koolrite 2290, per Jbolt's comments the water will dry up before it goes bad. Use it in my horizontal bandsaw with flood coolant and it works very well, and I get minimal rust. You need to be on the upper end of the dilution they recommend. Previously used Kool Mist 77 and it neither held up for long in the sump tank, and I had a lot more issues with rusting.
 
Whoever told you that carbide and coolants don't mix obviously didn't know what they were talking about. Now if they run the tool until it is really hot, then turn on the coolant, Yup could be a problem. But who the he!! would do that? My shop is in an Industrial area and I have been in many of the production/job shops. They all run coolant, even on the few manual machines that are still around.
What he said

While insufficient coolant or coolant that is blocked by the chip may cause a temperature gradient across the insert this is unlikely in a hobby shop setting. When you watch ytube videos of lathe demonstrations they are using no coolant because it would be nearly impossible to see the work because of the amount that would be used, gallons per minute.
Like so, parting is difficult without good flow.

The only time that I do not use coolant is when hard turning and these tools are not carbide but CBN. I use coolant on PVC, Delrin, UHMWPE, aluminum and free machining brass.
 
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