[dlavery]

Like so many other problems, the real answer is "it depends." Are you going to be applying it by hand, or using a misting system, or flood cooling? Are you looking for something to help with just drilling a few holes, or to help with thousands of holes and tens of hours of heavy-duty milling operations? Are you going to be hand-tapping everything, or using a tapping head on a mill? The best answer for one situation is not necessarily the best for another.

For my shop at home, I buy a gallon at a time of Mobilmet water soluable cutting oil. There are several equivalent medium-duty soluable oils that will do just as well. This class of lubricants will provide good general-purpose solutions that will cover the majority of typical situations you are likely to encounter when building a typical FIRST robot. If you are going to be applying the lubricants with a misting system, I would look for something heavier such as one of the sulfurized heavy oils (but don't use a sulfur-based oil on brass, bronze or copper unless you don't mind stains). The gallon may seem like a lot, but it is great to have a supply that lasts a while (and it is a lot cheaper by the gallon - or even five gallon - jugs than in the little 3-ounce bottles).

Check pages 689-692 of the Enco 2005 catalog (or just about any other industrial supplier - MSC, Grainger, McMaster, etc.). They carry all sorts of industrial lubricants, cutting oils, etc.

I would NOT recommend using WD-40 for anything other than a last resort, once in a while solution. It is a great penetrating oil for freeing stuck parts, but it is not intended as a cutting oil. Because it is so thin, it has a lot of volatiles that will evaporate very quickly, thus it should not be used in areas that are not very well ventilated. It will also leave residues on the work surfaces that can be a real pain to clean off later.

-dave