While doing some PM on the 4020 I decided to check the 10k spindle pre-load. per the fadal instructions it was .0035

1) Place a Pressure Gage (SVT-0066) on the table and align it with the Spindle
nose.
2) Set an indicator on the Head and touch the indicator tip on the nose of the
Spindle.
3) Jog the head (Z axis) down until the pressure gage reads 1000 pounds.
4) Zero the Indicator.
5) Jog the head (Z axis) up until it is no longer in contact with the pressure
gage.
6) Depress the “Tool In Out” Button on the keyboard.
7) Release Button.
8) Read the value on the indicator.
If adjustment is necessary on a adjustable spindle then turn the spindle
preload adjustment nut clockwise to tighten and counter clockwise to loosen.
Listed below are the "Fadal factory recommended specifications" for the
various spindles.
RPM Rating Preload setting: (Deflection at 1,000 psi. Lube Method
15,000 / 10,000. 0014-.0017 (Can Not be adjusted) Air/Oil
7,500 0013-.0015 (Adjustable preload) Grease Pac
10,000 0013-.0015 (Adjustable preload) Grease Pac
15,000 0017-.0019 (Adjustable preload) Grease Pac

Now the mistake I made was using the DTI deviation from applying the 1000# force on the spindle, setting the DTO to zero, and then reading the DTI when the Tool in/out button is pressed. Per the instructions above it should be read after the tool in/out button is released. Regardless there's too much spindle axial movement.

The spindle appears to have been adjusted before, there are marks on the slots in the split ring that suggest it's been driven around to increase preload.

I adjusted the preload to .0015 before I realised the reading is taken after the Tool in/out button is released. The preload is .0010 after releasing the tool in/out button.

The issue I'm having is as I back off the adjusting ring the preload isn't changing. I marked the position of the ring to the spindle before I moved it and I'm almost back to the original position of the ring/spindle where I had originaslly measured the .0035 preload. I wonder if the belt tension is creating a problem, or the bearing inner races aren't moving on the spindle as I back off the preload ring.

Anybody else adjusted the spindle preload and run into a similar problem?