Page:Practical Treatise on Milling and Milling Machines.djvu/121

Rh that might result from the foregoing cause would be present in the finished work.

Remove Backlash or Lost Motion from Feed Screws. Backlash or lost motion is apt to be present in the feed screws and nuts of any machine, especially in those that have been in use some time. To obviate errors in making fine adjustments, the operator should be very careful to eliminate all backlash before setting to the graduations on the feed screw dials. This may be done by turning the hand-wheel a quarter or half turn in the opposite direction to that in which the adjustment is to be made, and then bringing the wheel back to the point from which adjustment is to be made.

Use of Oil or Other Lubricant. Lubricant is used in milling to obtain smoother work, to keep the cutters cool so that the teeth will retain their cutting edges longer, and, where the nature of the work requires, to wash the chips from the work or from the teeth of the cutters. Oil is generally used in milling steel, wrought iron, malleable iron or tough bronze, where a smooth finish is desired. A soda water mixture can also be used to good advantage on these materials.

For very light cuts, oil should be applied to the cutter with a brush; for heavier cuts, it should be allowed to drip freely upon the cutter from a can, and on the heaviest cuts, a large supply of lubricant should be supplied by means of a pump, which can be affixed to the machine.

A good quality of lard oil is generally used, but any animal or fish oils may be employed. An excellent soda water lubricant that is less expensive and cleaner to use than oil, can be made by mixing together and boiling for one-half hour, $1⁄4$ lb. sal soda, $1⁄2$ pint lard oil, $1⁄2$ pint soft soap and water enough to make ten quarts.

Cutting Cast Iron. In cutting cast iron, lubricant is seldom used, as cutters do not usually heat very much, and the chips are so fine that the use of a lubricant results in a sticky mass that clogs the teeth of the cutter, and is difficult to clean from the work and machine.

Compressed air can be used to some advantage on cast iron, and will serve to keep the cutters cool and free from chips. In using compressed air care should be exercised not to have too much pressure, as it will scatter the dust and chips, which will fill bearings and cause trouble.

Collars and Washers for Arbors. Collars sent with milling arbors are not always the right thickness to bring cutters into the desired