Chapter Six, Cutting Fluids

Notes taken while studying chap. 6 of Machine Shop Basics visit them at www.audelbooks.com

Chapter 6
Cutting Fluids

In machining operations, cutting fluids reduce temperature and adhesion between the chip and the tool. This avoids thermal expansion and provides easier handling; cutting fluids also keeps away chips from the machining area. Sometimes a lubricant is part of the cutting fluid; this provides a rust proof layer to the finished work piece.

Coolant

A coolant chief purpose is to absorb heat from the work and the cutting tool. Coolant is usually in a liquid form; water has the highest cooling effect of any cutting fluid.

Lubricant

A cooling lubricant is a cutting fluid with the additional property that enables it to act as a lubricant. These materials usually consist of both cooling and lubricating agents, such as soluble oil or glycerin mixed in proper proportions.

Applications of Cutting Fluids

A stream of soluble oil is increases the cutting capacity of an abrasive wheel by preventing it from glazing over, and by carrying off the heat generated by the friction of the wheel on the work. It is important to apply the coolant to the work. A large stream of coolant at slow velocity is preferable to a high stream at high velocity. The cutting fluid should make contact with the work at the exact spot where the cutting is taking place, not above or to one side of the cutting tool.
On machining tools, cutting fluids keep heat from softening the cutting edge of the cutting tool. Cutting fluids cool the cutting tool and make it cut more easily and smoothly. The use of fluids washes away chips, prevents friction and allows higher cutting speeds.

Types of Cutting Fluids
Commonly used cutting fluids

o Lard oil- One of the oldest and best cutting oils, providing excellent lubrication, increased tool life, and provides a smooth finish on the work while preventing rust. Primary used for cutting screw threads, drilling deep holes, and reaming. Its use is somewhat limited because of the expense, the tendency to become rancid, and can cause skin irritation.
o Mineral-lard oil mixtures- Mixtures of various proportions of lard oil and petroleum-base mineral oils use in the place of lard oil alone, they are more fluid, less expensive and almost as effective.
o Mineral oils-Petroleum-based oils- Added with chemicals improving lubrication and anti-welding qualities. They are less expensive than lard oil and mineral oil mixtures.
o Water-soluble oils- Limited to use in rough turning operations, they carry away heat better than lard and minerals oils; however, lubricating qualities are poor. They are mixed with water to form an emulsion and prove to be an excellent low-cost coolant.
o Chemical cutting fluids- These are mixed with water and generally do not contain any petroleum products. The chemicals used provide excellent lubricating and anti-welding properties.
o Low-viscosity oils- Kerosene and other types of oils are used for cutting tough nonferrous metals and alloys such as bronze, aluminum alloys and alloys containing a small percentage of iron such as Monel metal.

Solid Lubricants

Grease-type lubricants are used on band saws to lubricate the sides, back edge and guide bearing especially where high speeds are involved. Graphite is often combined with these lubricants and is supplied in tubes.
Wax and soap lubricants are combined with petroleum substances and are supplied in stick form. A good solid lubricant is recommended for sawing metals, hardwoods ect, where the use of a solid lubricant is preferred to a circulating type.