Disable the linear scale in the control. Set parameter 268:0 LIN SCALE EN to 0.

Set parameter 127 Z GRID OFFSET to 0. 

Jog Z-axis to top of travel.

Unbolt the Z-axis way cover and lower it.

On VF-3/4/5 machines, remove the top, left and rear spindle head cover.

Disconnect the linear scale cable from the extension cable and remove the cable clips and ties that secure the linear scale cable.

Remove the Z-axis limit switch and the trip switch bracket for accessibility if needed.

Remove the two metric screws and nuts or nut plate attaching the encoder head to its bracket. The spindle head may have to be jogged to facilitate removal.

Unscrew the two bolts that hold the encoder bracket to the spindle head and remove the bracket.

Remove the linear scale leaving the scale mount in place.

Clean mounting bracket, and remove any burrs that would affect scale installation.

Using a dial indicator check the parallel runout of the scale mounting bracket. To indicate the full length of the scale mount; jog spindle head to the top of its travel and place the magnetic base on the bottom of the spindle head.

Zero the indicator, mark the position of the indicator stylus on the scale mount and obtain reading, full travel down.

Remove magnetic base and place it on top of the spindle head.

Zero the indicator at the mark on the scale mount and obtain reading, full travel to the top. (T.I.R. .004). Align if necessary.

Verify bolts are tight. If alignment cannot be made within tolerance, shim stock may be used near mounting bolt locations when mounting the scale.

Check the scale and verify that it is a new 'C' version with plastic isolating material on the encoder head mounting surface. See installation diagram below for the part number.

The pigtail cable should also have a version 'C' label on it. Do not remove the labels.

Install the linear scale using Blue Loctite on the screws.

Check and adjust scale parallelism. Use shim stock as required to obtain parallelism TIR .004.

Use a new style electrically isolating encoder bracket for mounting the encoder head. See installation diagram for the part number.

Check all mounting surfaces for burrs that may influence the angle of the bracket. Install encoder bracket to the saddle leaving the bolts loose enough to adjust the bracket (use a flat washer with Blue Loctite or a split-lock washer).

Using the horizontal gap tool "set tool" (T-2064), align the encoder bracket to the scale (see figure) by pinching the tool between the encoder bracket and linear scale and slowly tightening the encoder bracket mounting screws by alternating between screws to prevent shifting the bracket.

Be sure alignment is not made where there are labels on the scale. Leave the "set tool" in place and check that the bracket surface and the scale surface are parallel. If they are not, use a feeler gauge to measure how out of parallel they are. If they are more than .004" out of parallel shim the encoder bracket.

Remove the "set tool" and verify allowable gapping error by inserting the "go tool" (T-2063) from both sides of the bracket. Insertion of this tool means the gap is not too small.

Attempt to insert "no go tool" (T-2065) from both sides of the bracket.

If the tool does not fit then the gap is not too large.

This completes alignment of the encoder bracket. 

 Note: For VF 3-5 machines the gap tool cannot be inserted from the far side.

The new isolating encoder bracket uses metric screws with flat washers, plastic shoulder washers, and nuts or nut plate as shown in the installation diagram.

Align encoder head to scale by pinching vertical gap tool "set tool" (T-2067) between the encoder head and scale and tightening the screws (use Blue Loctite). Be sure any isolating material overhanging the encoder head is not pinched between encoder head and gap tool.

Remove "set tool" and verify allowable gapping error by inserting "go tool" (T-2066) from both sides of the encoder head.

Insertion of this tool means the gap is not too small.

Attempt to insert "no go tool" (T-2068) from both sides of the encoder head. If the tool does not fit then the gap is not too large.

This completes alignment of the encoder head.

 Note: For VF 3-5 machines the gap tool cannot be inserted from the far side.

Do not connect linear scale cable to extension cable at this time. Verify isolation or electrical discontinuity between encoder head and its bracket using an ohmmeter.

Connect linear scale cable to extension cable, check cable routing, and secure the cable.

Check that the cable will not interfere with other parts when the spindle head is moved. Be sure that the cable does not bend too tightly (see illustration). 

Mount the Z-axis limit switch and bracket if necessary.

Enable scale, set grid offset, verify full travel and set parameter 64 Z AXIS TOOL CHANGE OFFSET.

Replace the head covers and reattach the way cover.