|The milling machine lathe is a precision machine tool and must be
treated with great care to maintain the machine’s accuracy. Regular
cleaning and maintenance will help to assure that the milling machine will
maintain its service life and accuracy for many years. This unit will
cover basic milling machine maintenance. The procedures you find within
this document should be able to be performed by apprentice or beginning
machine tool students. Milling machine maintenance that requires more
extensive disassembly should only be done by, or under the supervision of,
|The drive belts supply power from the motor to the spindle. Access
to the drive belts is gained by opening the side door on the column of
the milling machine (Figure 1).
Make sure that all power is locked out before removing any guards.
Figure 1. Side Access Door.
|Drive belts come in matched sets and should only be replaced with a
matched set of belts. Visually inspect the drive belts for excessive wear
and cracking. If you notice that one or more of the drive belts appear to
be excessively worn or cracked, bring this to the attention of the
instructor. Check the belt tension by applying finger pressure to each
belt at a point midway between the two pulleys (Figure 2). For correct
tension a deflection of about 3/4 of an inch should be evident in each
belt. If the amount of deflection is more than 3/4 of an inch in any one
or more of the belts, bring this to the attention of the instructor.
Figure 2. Each belt should have approximately the same amount of
|All milling machines employ precision slide ways. The saddle, table,
and the knee all ride along a box slide way or dovetail slide way. After
time the parts that ride along the slide ways begin to wear. To compensate
for this wear, machine tools are equipped with adjustable parts called
gibs that allow you to eliminate the space that has been created by the
wear between the slide ways (Figure 3).
Figure 3. A tapered Gib located on the table of the milling machine.
|There are two types of gibs, straight gibs and tapered gibs. Straight
gibs are adjusted by screws spaced out along the length of the gib. The
screws push the gib in to create more contact with the sliding mechanisms
Figure 4. A knee slide utilizing a straight
|Tapered gibs use one or two screws. The screws are located in each end
of the tapered gib. One screw acts as an adjustment while the other screw
acts as a locking mechanism. Because tapered gibs are wider on one end
than the other, they slide in or out creating more or less contact between
the sliding mechanisms (Figure 5).
Figure 5. Tapered gib with screws.
Table Gib Adjustment
Figure 6. Table Gib Screw.
|Wear in the table slide ways must be adjusted by using the screw on the
left face of the table slide. (Figure 6).
On larger machines, the procedure is to first loosen the similar gib
screw on the right side of the table, then re-tighten the opposite gib
screw to lock or adjust the Gib in its new position. On small ram-type
milling machines there is only one adjusting screw on the left-hand side
of the table. The procedure is identical to the larger machines only there
is no locking screw. After the adjustment, traverse the table over its
entire length to be sure of smooth, even operation.
Saddle Gib Adjustment
|Wear in the saddle slide ways must be adjusted by using the screw on
the front face and rear faces of the saddle slide way. On small ram-type
milling machines there is only one adjusting screw on the front of the
saddle. The procedure is identical to the larger machines only there is no
locking screw. (Figure 7).
Figure 7. Saddle Slide Way Gib Screw.
The procedure is to first loosen the rear gib screw on the saddle slide
way, then re-tighten the front screw to lock or adjust the Gib in its new
position. On the small ram-type milling machine adjustment can only be
made from the front gib screw. Note if a chip wiper is present, you will
have to remove it before any adjustments can be made (Figure 8). After
making the adjustment, traverse the saddle over its entire length to be
sure of smooth even operation.
|Most milling machine are equipped with Wiper pads (Figure 8). Wiper
pads are typically made of felt that will hold oil.
Figure 8. Rubber wiper pads with felt inserts.
Wipers are designed to keep out small chips and dirt between the slides
and the ways. Wipers are saturated with oil to catch the fine particles of
dirt or debris before they get between the two sliding surfaces. The
wipers should be removed, cleaned and re-saturated with oil regularly. You
should never use compressed air for cleaning a milling machine. Compressed
air will push the fine particles trapped in the wiper between the mating
surfaces of the slides, and causing premature wear on these precision
Knee Gib Adjustment for Ram Type Milling Machine
|Ram style-type milling machines are equipped with a tapered gib on the
knee. To adjust the gib remove the wiper and adjust the top gib screw
until smooth movement over the entire travel is attained (Figure 9).
Figure 9. Knee gib for a ram-style milling machine.
Knee Gib Adjustment for Large Knee-Type Milling Machines
|Large knee-type milling machines are equipped with a straight gib on
the knee. To adjust the gib a series of bolts with lock nuts must be
adjusted individually (Figure 10). This gib adjustment should only be
done under the supervision of a trained machine tool mechanic or
Figure 10. Straight gib on a large knee-type milling machine.