13 years ago
There is some strange quirk in the RCM emotional makeup, which I've never seen elsewhere in 35 years of visiting machine shops and plants, that abhors the idea of buying a fluid that's formulated for the purpose for which they're going to use it. I appreciate the joys of discovering something that's sold for some other purpose and that winds up being scads cheaper -- my barbecue baster is a 99-cent Chinese bristle brush screwed to a piece of scrap trim that Home Depot was giving away -- but this is fairly serious business. What makes anyone think that automatic transmission fluid, bacon fat, vegetable shortening or used crankcase oil is going to have the right properties for good, safe, efficient, and effective machining? And how much are you going to use, anyway, in hobby machining? My Buttercut tends to go rancid before the can is empty.
This is the only place I've ever heard of it. The reasons for not using stearin-entrained lard oil (bacon fat, lard) and for not using oils formulated as machine lubricants, have been known for 100 years or more. If people actually did comparisons between real cutting oils and some of the slop that's discussed here, I think things would be different.
Some of it may be the lack of easy availability for traditional cutting oils -- lard oil, sulfated lard oil, chlorinated oils, and mineral oils actually formulated for cutting. 30 years ago I could walk into either of two stores nearby, an old-fashioned hardware store in town and a mill supply five miles away, and buy a small can of Buttercut or DoALL sulfated mineral oil. No more.
-- Ed Huntress