Adjusting Fadal spindle preload

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?

I usually go by “if it ain’t broke, don’t fixit”. Especially when it comes to spindle preload. Yes, you are suppose to preload the spindle to 1000#, zero the indicator, then hit Tool in out, and release. The reading on the indicator is the preload. I have seen as much as .005” with no issues. Another thing that usually occurs after preload adjustment is the spindle will lockup because it is too tight. That being said, at this point run the spindle starting at 1000 rpm for 30 - 45 minutes while monitoring the temperature of the spindle nose. Increase the rpm by 1000and repeat until max rpm is reached. When getting up to 7000 rpm, the heat will increase, you want to make sure the chiller is working properly and maintains temp. I forget the max temp that is safe, but you should be able to hold your hand on the spindle, if your not able to hold your hand on it, it’s too tight and needs to be readjusted, then tested in the same way as above. Most times I hear of people adjusting the spindle preload, they are replacing the spindle shortly after. Just my .02

I've been running 8k rpm with no issues, with the chiller on it gets barely warm to the touch. So far so good. I agree, in retrospect I should have left it alone. The finish is slightly improved, and for what it's worth the spindle is a lot quieter. I ran it in again in increments, rather than running it hard from the get go.

I have a spare rebuilt spindle on the shelf in case this one decides to give up the ghost.

Where do you get a pressure gauge? I had a spindle give up and rather than purchase a reman and send in the old one as a core as I suggested, the owner told me to replace the bearings. I did that and it sounds ok, but the surface finish is terrible now, I am almost certain that its the spindle pre-load. I looked on fadalcnc and itscnc and neither one carry one, at least not under the SVT-0066 part number or the label pressure gauge.

I guess it could be unbalanced as well, since I don't have the setup to properly rebuild a spindle here, but I don't sign the checks so I don't make the decisions

The bore of the Aluminum cylinder is 1.128", the o-ring is on the steel piston. The area of the bore is 1.0in2, so 1000# of force will read 1000# of pressure. The bar across the top goes across the diameter of the spindle face.

Attachment 394740

Having similar chatter problems with a cut I have made 100 times with no problems? I suspected spindle bearings and completed this check. - I used an electronic race car scale instead of the pressure gauge but 1000 lbs is the same if the scale indicates it. Worked great, I put a block of 2x4 on top to protect spindle .
So at 1000 lbs my indicator moved .0005 from where I started. I zeroed it and then released the 1000 lb load. It moved back the .0005. Pressed too in/out and released it. Indicator returned exactly back to the .0005 position.
Note I had .002 movement down with tool in/out depressed, but only .0005 when released .
This seems tighter than the spec. But has always cut good even after my goofs and broken tools.

So trying to figure what to check next? I bought new 3 flute carbide tool and new tool holder. Did not help.

Any help appreciated.