Plain milling machines, both vertical and horizontal, do not require table alignment in normal use because the table cannot be swiveled. Overarm-type vertical milling machines that do not have either a swiveling or fully universal head do not require head alignment because the head can move up and down only.
The table on universal milling machine must be checked for alignment whenever it is being returned to 0˚ position or when a job involving precise angular relationships is to be done. NEVER trust the graduations on the saddle or on any other parts of the machine when really accurate work must be done.
A rigid mounting for the dial indicator is necessary so that flexing and slippage do not alter the readings. The 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 head on vertical milling machines with semi universal or universal heads must be checked before doing jobs requiring accurate alignment between the head and table. It’s important to align the spindle perpendicular the table when drilling, boring, and flycutting operations are performed. The following procedure is suggested for alignment the head of vertical milling machines with semi universal or universal head.
- Clean the table thoroughly and place a flat and parallel plate on it if one is available.
- Attach the dial indicator to spindle.
- Feed the spindle down, with the dial pluger at operator’s right of left side until it registers about one-fourth of its operating range, and zero it.
- Carefully rotate the spindle one revolution.
(a)If the head and swiveling or semi universal type, the fore and aft readings in line with the cross feed will be identical; the right and left readings may vary if the head is not vertical.
(b)If the head is of the universal type, the reading may vary on both axes.
- Adjust a semi universal head by loosening the head and swiveling it so that the dial indicator reading is cut in half. Recheck the spindle and readjusting the head if necessary.
- Universal heads should be adjusted in one plane at a time.
- Securely tighten all head locking bolts and recheck.
Vise and Fixture Alignment
Vise alignment-the 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 procedure is suggested for aligning plates and other fixture with major flat surfaces
- Clean all parts thoroughly. Make sure that there areno burrs or nicks on mating surface.
- Lightly clam 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 in about one-forth of the indicator’s operating range and zero the indicator.
- 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.