Yet another Denford for the collection (Triac Retrofit thread)

[m_c]

So getting back to the mechanics, the spindle was stripped, and rebuilt with new bearings and fresh grease. I only took one photo of it, which is this one, showing the spindle removed, but the lower bearing, and lower bearing retainer still on the spindle.



The process goes something along the lines of-
Remove drawbar cylinder.
Unbolt top support bearing and housing, and extract using bolts into the threaded holes provided for the purpose.
Remove spindle motor and drive belt (you have to unbolt the motor to get the belt of)
Remove notched adjustment nut, along with locking tab ring.
Unbolt the lower spindle bearing retaining/seal plate.
Knock/press the spindle down out of the head assembly.
Pull the lower bearing of the spindle.
And reassemble in reverse.

After reassembly, you need to preload the bearings. The method used by Denford was to adjust by feel.
Now as I deal with things like this occasionally, I've got a reasonable idea of how a preloaded bearing should feel, but I'll give some tips for those who've never done it before.
Once you have the spindle assembled, with the adjustment nut on, nip the nut up. Then using a hammer and punch on the top face of the nut, give it a tap at various points around the nut. Nip the nut up again.
Now using a block of wood on the face of the spindle, give it a couple taps upward, before seeing if you can get anymore movement on the nut.
Repeat a couple times until you're happy things are settled, with no more movement on the nut.
What this does, is help ensure everything is seated correctly. Given the interference fit of parts, it's very possible that you could preload the bearings, but without something seated correctly. What that would mean, is that you rebuild everything, and then after a period of time (it could be after a few minutes, or even a few months), the whatever it is will settle in, your preload disappears and you end up with a load of spindle run out, where it's flapping around in the bearings.
At this point I gave the spindle a good few spins to help work the fresh grease out from the bearing tracks.

Now taking a DTI mounted on the head (so any movement in slides doesn't affect the reading) and set against the side of the spindle, using a best guess effort as too how much pressure the spindle is likely to see, I grab the top of the spindle and pull/push it in the direction of the DTI needle.
I then adjust up the lock nut until I'm getting minimal movement. I spin the spindle a few times, give things another tap with the hammer/punch/block of wood, and recheck. Once no more adjustment is needed, I spin the spindle by hand. I then adjust up the nut until I feel a very slight bit of springiness just as the spindle starts to move. Once again, I give everything a tap, and recheck. Once I'm happy, I bend a locking tab into a notch.

The real proof in whether you've got it right, is in the running.
Once you get the motor back on, you should run the spindle at a lowish speed (I opted for about 500rpm) for 10-15 minutes to let the grease work it's way out from the bearing tracks, while also monitoring the spindle temperature.
If you run the bearings too fast too soon, they can slide on the grease, which results in premature wear and even causing flat spots on the bearings, which will lead to vibrations and poor cutter finishes.
If everything sounds OK, gradually ramp the speed up, allowing maybe 5 minutes at every step (I went up in 500rpm steps), while monitoring the temperature. If you've got the preload within acceptable limits, after an hours running the spindle/housing should of warmed up, but you should still be able to keep your hand on it. If at any point you can't keep your hand on it, you've got too much preload, so stop it and slacken the adjustment nut of a notch. If on the hand it barely warms up, you've not got enough preload, which means you're most likely going to get a rubbish finish on parts as the spindle/cutter deflects while cutting.