| Table of Contents |
|---|
Background
Each PCNC machine is tuned at the factory to meet or exceed certain precision metrics. These metrics are indicated on the Certificate of Inspection that is included with each mill, along with the actual values measured for each metric as part of Tormach’s Quality Assurance program. The following advanced maintenance procedures may become necessary over the ownership lifetime to maintain the original factory precision:
...
Backlash: the major component of lost motion in a machine tool axis. It results from the clearance between moving mechanisms. This is sometimes referred to as play. There are two sources of conventional backlash that can be adjusted on the PCNClathe:
Space between gib and way needed to support an oil film. This is tuned by tightening the gib.
The space between the ball bearings and races in the angular contact bearing pair that supports the ball screw. This is tuned by increasing the angular contact bearing pair preload.
...
The following method describes the proper procedure to measure Z-axis backlash. An analogous procedure is used to measure X-axis lost backlash.
...
Mount a dial indicator to the machine bed along the Z-axis with the tip in line with the x axis carriage. Be sure that the indicator needle will touch a machined surface.
. Jog the X- and Z-axis to position the carriage so the indictor tip contacts the edge of the carriage.
Carefully jog the Z-axis in the negative direction until the indictor contacts the spindle. After initial contact, continue to jog the Z-axis in the negative direction so that the dial makes at least one complete revolution; stop when dial reads 0.
Zero the X DRO field in PathPilot
In MDI field, program a negative Z move of .01” at a feed rate of 5 IPM: G01 X.01 F5. The carriage moves slightly in -Z direction. When finished, indictor should read .010”.
Program a Z move back to 0: G01 X0 F5. The carriage moves slightly in the +Z direction. The Z DRO should say 0; however, the dial indicator should read a number very close to 0. This value is the measured lost motion.
Gib Adjustment
| Anchor | ||||
|---|---|---|---|---|
|
The adjustment procedure is similar for both axes. The Z-axis is described in detail. The gib plate is tapered from right to left. When the gib plate is moved in the Z negative direction (to the left of the operator), the Z-axis saddle the slide way tightens; when it moves in the Z positive direction, the slideway loosens.
...
Loosen the right screw eight turns and tighten the left screw eight turns so that the gib clearance is loose.
Use a dial indicator to measure the axis backlash. With a very loose gib, the measured backlash is entirely attributable to the backlash in the belt reduction drive, the angular contact bearings, and the ball nut. On a newer machine, the value should be under 0.0025” on either axis.
Tighten the gib by one turn (by loosening the lower screw first, then tightening the upper screw). Measure the backlash again.
Repeat this procedure until the measured backlash increases – this is the point at which the gib setting has started to induce lost motion in the axis.
Back the adjustment off to the point just before you saw the increased backlash. That is the ideal setting for the axis.
...
| Info |
|---|
IMPORTANT! Ensure both adjustment screws are tight after any gib adjustment. Failure to do so will result in gib movement. |
...
| Expand | ||
|---|---|---|
| ||
To properly estimate the torque needed to overcome angular contact bearing friction, the bearings must be isolated from the motor detent torque. The following procedure illustrates the Z axes of the 15L; other axes will follow suit:
|
Backlash Compensation
| Anchor | ||||
|---|---|---|---|---|
|
...