Mill Upgrades – Spindle Upgrade Part 4

Time to switch the tapered roller bearings (TRB) out for angular contact bearings. The primary benefit is that AC bearings allow higher speeds, particularly when running only with grease. First step was to pull off the seal above the top spindle bearing, remove the nut and pull the spindle out.

I dunno what kinda grease was in here, but there’s certainly a lot of dirt, probably largely as a result of having too much grease. This machine has probably only run for a couple hundred hours, so realistically the grease pack it had now should have lasted a while, and you can see in the first picture that the rollers look pretty clear (the grease forms a thin film on the rotating elements of the bearing).

I didn’t take any pictures apparently, but to get the quill out of the machine, you need to remove the quill retaining bolt (on the left side of the head), then loosen the quill lock. If you have the quill arm that may need to be removed, but as I have already removed mine I’m not sure. I have also already removed the quill DRO and the clamp that holes it

The next step is to knock the TRB cones out of the quill.

I cleaned up the quill face a bit after this, but you can see how much grease was jammed into the rollers and cages when I removed them, and how dirty the inner bore is. Most of the inner bore was hard enough it didn’t come off by wiping, and that stuff I left in there. Whether that was a good choice remains to be seen.

Time to press in the new AC bearings. Note: it would have been a better plan to grease them before doing this.

And back into the machine.

Now, I put way more grease than necessary because I forgot to grease them before, and my hope was that some excess would move under gravity in the top bearing, and that I would force some through by hand in the bottom bearing. I also wiped away a lot of the grease after running the spindle at 500 RPM for a little while to warm things up and spread the grease onto the balls. You’re only supposed to fill about 1/3 of the open space in the bearing (according to SKF, who should know), however ultimately the grease will convert to a thin film and coat the bearing, and any real excess will be forced out, particularly at high RPM. Excess grease will hold onto dirt and potentially migrate back into the bearing which isn’t great. If the space confines the grease in the bearing it will also cause excess heating, even if it’s clean.

Here’s what they look like after a few hours of running. I ran the spindle up to 7k in 500 RPM increments over the course of 5-6 hours (I was working on other stuff around the shop, the only rule I had was that I waited at least 10 minutes to measure temperature, and if I had already measured noise then I confirmed the measurement).

Spindle bearing noise comparison.png

The noise produced with the AC bearings is lower than the TRBs, although the modified motor and spindle pulley mounting may be a factor in that. Both are way better than the geared setup, which ran at 85 dB at 3k RPM.

One interesting thing to note was the peak around 6k RPM — some sort of resonance frequency perhaps. I remeasured that point going up and down several times to confirm, but it really does get quieter if regardless of whether the RPM is reduced or increased from there.

Spindle bearing temperature

Both bearings are in a good temperature range for the application, and there’s certainly head room to run the spindle faster. I’ve gotta scratch my head some more about why the smaller bearing is hotter.

Time to pop the seals back on and try out ripping some aluminum.



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