5) Alignment involved in milling operation

a)Machine Alignment
-Alignment is needed for the worktable and head of those milling machines.
-Alignment is not needed for the plain milling machines, both vertical and horizontal because the table cannot be swiveled.
-Overarm typer vertical milling machine does not need it because the head can move only up or down.
b)Table alignment
-The table on universal milling machines must be checked for alignment whenever it is being returned to the 0 degree position.
-Do not trust the graduations on the saddle or any other part.
-A rigid mounting for the dial indicator is necessary so that flexing and slippage do not alter the readings.
-Dial indicator must be mounted to the table of the machine because the motion of the table relative to the face of the column is being checked.
-The following eight step should be followed:
· Clean the table and column face and make sure there are no nicks that rise above the surface.
· Attach the dial indicator.
· Make sure the dial indicator is in contact with one edge of the column face.
· Move in one-fourth of the indicator’s operating range,and zero the dial by turning the bezel.
· Move the table manually and note any changes in the dial indicator reading.The gribs on the knee,saddle,and table must be in good condition and properly adjusted to eliminate lost motion.
· Table cannot be adjusted accurately if there are any loose mating surfaces.
· If any error is noted,loosen the saddle clamps and move the table one and a half of the error in the proper direction and retighten.
c)Head alignment
-Semiuniversal or universal heads must be checked before doing jobs requiring accurate alignment between the head and table.
-The spindle must be aligned perpendicularly to the table when drilling,boring and flycutting operations are performed.
-The dial indicator must be rigidly attached to a fixture held in a collet in the spindle.
-The diameter of the circle that the dial indicator makes should be slightly smaller than the width of the table.
-Table must be clean and free of nicks before the aligning operation is started.
-Steel or cast iron known as flatness and parallelism can be placed on table to avoid plunger on the dial indicator from drop into the Tslots.
-The following procedures is suggested for aligning the head of vertical milling with semiuniversal or universal heads:
· Clean the table and place a flat a parallel plate on it.
· Attach the dial indicator to the spindle.
· Feed the spindle down,with the dial plunger at the operator’s right or left side until it registers about one-fourth of its operating range,and zero it.
· Rotate the spindle one revolution and for this if the head is universal type,the reading may vary on both axes.
· Adjust a semiuniversal head by loosening the head and swiveling it so that the dial indicator reading is out in half.
· Universal heads should be adjusted in one plane at a time.
· Securely tighten all head locking bolts and recheck.



Vise and fixture alignment
-Solid jaw of the vise is always the reference surface.
-The dial indicator is attached to the arbor of a horizontal milling machine or held in the collet of a vertical milling machine.
-The following procedures is suggested for aligning plates and other fixture with major flat surfaces:
· Clean all parts thoroughly and make sure that there are no burrs or nicks on mating surfaces.
· Lightly clamp the vise or fixture in approximately the correct position.
· Bring the dial indicator in contact with one end of the part to be aligned.
· Move the table or cross slide the full length of the jaw or fixture.
· Note the variation in indicator reading and move the vise or fixture in the appropriate direction using a soft hammer.
· When the indicator shows no deviation,retighten all bolts and recheck.