Page:Practical Treatise on Milling and Milling Machines.djvu/46

40 of driving shaft. If, for instance, the speed of the main shaft in a shop is 200 R. P. M., and it is required to drive a counter-shaft, having a pulley 14 inches in diameter, 320 R. P. M., the diameter of the main shaft pulley is found as follows:

$${320 \text{R. P. M.} \times 14'' \over 200 \text{R. P. M.} }=22.4''$$, diameter of pulley required on main shaft.

when the counter-shaft has two or more pulleys whose speeds differ, a separate calculation is required for each. And when no counter-shaft is used, the calculation is the same as abovce, except that the required speed and diameter of the machine pulley are substituted for the diameter and speed of the counter-shaft pulley.

Importance of Keeping Machine Clean and Well Oiled. Many workmen fail to appreciate the importance of keeping a machine clean and well oiled, and we cannot emphasize this point too strongly. Proper attention to these details influences the accuracy and efficiency of a milling machine and prolongs its life, while neglect to attent to these matters has ruined many a good machine.

Working parts most exposed to dust, dirt or chips, should be frequently cleaned and oiled. Chips should not be allowed to collect upon the surface of the table until they fall over the sides on to the flat bearings on the top of the knee. Care should also be taken to prevent chips and dirt getting between the knee and column, causing scoring of these flat bearings and throwing the knee out of alignment.

Oil tubes and channels many times become clogged with a gummy substance, due to the accumulation of dirt in the oil, and also to decomposition of the lubricant itself. This can be effectively removed without injury to the bearing surfaces by flushing the tubes and channels with gasoline or naphtha. It is well to do this occasionally to insure free passage of oil to the bearings, for if the bearing surfaces, especially cylindrical ones, run dry, they become roughed up, which necessitates taking them apart, and entails considerable work before they can be made to run satisfactorily again.

A machine that has been in active service for a period of a year or two, should be thoroughly cleaned and inspected. To do this, requires that it be taken apart to some extent, as it is impossible to ascertain the condition of some of the more important bearing surfaces in any other way. Also it is the only way in which one can make sure that some of the oil channels that are not easily accessible are not filled up.