Reply To: New Mill

[david pierce]

Paul,
Any cutting action is a resust of force applied against something to be cut. The principal works on pressure over area. This means that the smaller the area the greater the force. When a tap cuts out a thread or a graver or cutting tool peals off a chip, the metal is actually being ripped away. This is why a nice shinny watch pivot looks like a mountain range under magnafication. The purpose of a lubricant is to reduce the friction between the moving surfaces and tear the metal away in a more controlled manner. If you take oil and lower the temperature it will turn into a solid just like parafin. Parifin just happens to be in a solid form at normal temperature. It is in fact an oil and due to its lower cost is the fuel of choice for large ships. It is simply heated up and pumped into the cylinders as a liquid. It does have lubricity in its natural solid form but when heated by the friction of the cutter movement it turns into a liquid and provides more coverage between the moving parts. As far as which oil to use, companies have spent a lot of time and money on research on which combination of chemicals work best on which materials in different situations. When something is especially formulated to tap steel or aluminum or titanium or various other metals it is due to the fact that companies have had problems with tap breakage or nasty looking threads. I have found that oil works well in most situations and does not cost a lot so I use it. If I have problems with the process then I will look for other and usually more expensive solutions. When you buy a can of cutting oil it will have a mix of other things in the oil such as sulfur to make it work a little better than the cheap stuff that I normally use.
david