In many ways, I think cutting oil and cutting tools have similar
demographics (word chosen deliberately despite being incorrect). The application and usage matters a lot. Industrial users need to optimize cost, tool life, surface finish, and efficiency. Hobby users prolly only care about cost and surface finish. But I think almost everyone also cares about health, the environment, and smell. So the right cutting fluid depends on who is using it, for what, and how they prioritize the different attributes.
For steel, my personal preference by a very wide margin is Vipers Venom. I first learned about it through the smithing community. I think I can safely say that it is the clear favorite of the majority of smith's out there. It's benefits and advantages are extensive. It absolutely excels at cutting stainless. It has high sulphur and is fortified with chlorine to reduce metal pick-up, galling, and welding. It has excellent cooling properties, tolerates extreme pressure, and has great lubricity. But I think my favorite attribute is its anti slinging and spreadability. It sticks to the metal like glue and resists being flung off as the work rotates so it lasts through multiple passes. On the negative side, it does have a fairly strong odour (that I happen to like) and it probably isn't the greatest stuff for the environment if you pour it down the sink. It's biggest negative for Canadians is its availability. Individuals used to be able to get it from a fellow in BC, but he doesn't sell it anymore. The only way I know of today is to order it from grizzly. Unfortunately, they ship by UPS who are not the best carriers around. Yuk!
I've been using VV for at least 30 years with zero regrets. In fact, it's the only cutting oil I use for steels of all types today. I love it so much that I bought a lifetime supply last year and also placed a bulk order to help other members get some. I'd do that again if there was enough interest.
As solid as I am for cutting and drilling steels, the jury is still out for me for cutting fluids for Aluminium. I used to use WD40 but that ended the first time I tried tap magic for Aluminium. It's WAAAY better! My recent experience with the way that wd40 separates when left sitting has only deepened my preference for tap magic. However, I don't have nearly the same love for tap magic that I have for VV. I could easily be talked into trying other fluids for Aluminium. I would love to find something that worked like VV. However, I would resist anything I could only use as a volume coolant.
