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Adjusting X-axis & Z-axis Gibs

Alloy Wheel Repair CNC Lathe

One of the most important maintenance jobs for mechanical components installed on all Alloy Wheel Repair CNC lathes is to keep both X-axis and Z-axis Gibs clean and lubricated in order to keep them in perfect working conditions. Needless to say, the quality of alloy wheel surface finishes is depending upon the performance from linear motions of both X-axis and Z-axis movement under both automatic mode (using program) and manual mode.

Wheel CNC Lathe

Lehigh MR-2540 
Alloy Wheel Repair Diamond Cutting CNC lathe

When a new Alloy wheel repair CNC lathe, such as, Lehigh MR-2540 or Lehigh MR-2940, is delivered, gibs at both the X-axis (cross slide) and Z-axis (saddle) have been adjusted to their best working positions. After 3 to 6 months of operation, however, they could become loose due to vibrations and/or wear and tear depending on working hours. It is very important to check them on a regular basis and make necessary adjustments in order to provide best machining accuracy and working conditions.

A. X-axis Gib on MR-2540 Alloy Wheel Repair CNC Lathe

At cross feed direction or X-axis, there is only one gib, which is located on the right hand side of the cross slide with full length of the cross slide, which is referring to the long table on which the tool post is mounted on.

wheel repair machine

Alloy Wheel Repair CNC Lathe -Tool post and cross slide

jib location

Front View – X-axis Gib (on right side)

X-axis jib location

Rear View – X-axis Gib (on Left side)

For Alloy Wheel Repair CNC lathe, Lehigh Model MR-2540, the X-axis gib is about 38” long in total length of the cross slide. The front end of this X-axis gib is much thicker (say, 9 mm) in comparison with its rear end, which is much thinner (say, 3 mm). And it is tapered uniformly along the full length. Therefore, its physical working position along the cross slide will determine how much friction force between the dovetail ways and the cross slide. When it is too tight, then, it would be very difficult for X-axis servo motor to move the tool post along cross feed direction. When it is too loose, the servo motor may not be able to keep tracking its steps. This is why it is very important to make sure that the position of the X-axis gib is adjusted on a regular basis to ensure its best working conditions.
 
Also, one side of the X-axis gib shall be protected with a thin Teflon cover for longer working life.
jib

Full view of X-axis gib with heavy end at front and thin end at back

X-axis Gib with Teflon Cover

How to make adjustment on X-axis jib

Diagram for gib adjustment at X-axis (cross slide)

Step 1.  Remove screw #1 and cover #2 on the back side in order to see #3..
Step 2.  Use a flat head screwdriver to release screw #3 about a ½ circle CCW.
Step 3. Tighten screw #4 at the front about a ½ circle CW (clockwise this time.)
Step 4. Move the cross slide backwards and forwards to reach the desired smoothness.
 
 
B. Z-axis Gibs on MR-2540 Alloy Wheel Repair CNC Lathe
Jib adjustment

There are two gibs installed along Z-axis for longitudinal traveling. One is located in the front guideway (Left side from above picture ) and one is located on back side (right hand side).

Even though the working principle for both X-axis gib and Z-axis gibs are the same. However, the actual dimensions and their shapes are totally different. The gibs along the Z-axis are almost squared with very small variation between two ends and they are much shorter than X-axis gib as well.
 
To locate the Z-axis gibs both at the front side of the bed ways and at rear side of bed ways, one needs to refer to the following pictures:
jib adjustment

The Z-axis gib located at front side

jib adjustment

The Z-axis gib located at front side

jib

Here is a comparison between X-axis gib (at top position) and Z-axis Gib (below). The X-axis gib is much thinner and much longer with one piece needed. However, the Z-axis gibs are much heavier and much shorter. Also, there are two Z-axis gibs needed for each CNC lathe. In general, the adjustment for X-axis gib should be more frequent than that of Z-axis gibs.

How to make adjustment on Z-axis jib
jib adjustment

Diagram for gib adjustment at Z-axis (cross slide)

Step 1.  Use a flat head screwdriver to release screw #3 about a ½ circle CCW.
Step 2. Tighten screw #4 at the front about a ½ circle CW (clockwise this time.)
Step 4. Move the saddle backwards and forwards to reach the desired smoothness.