Mill spindle rattle question

OK, this is a "Pinnacle Universal Mill" that I recently acquired, I'm
guessing it is about 20 years old, BTW if anyone knows where I can get
a set of manuals much appreciated.
Spindle is powered from a Jinshin 4 pole 1 hp 240 vac single phase
motor, with 5 speed belt drive using a A29 vee belt.
At the lowest speed, 200 rpm, it is silent, but as you ramp up the
cogs / spindle speed it develops a pronounced speed related rattle.
I tried the motor spindle by hand, no slack and no bearing
"cogging" detectable, and spins up as smooth as silk with the belt
detached, possible by eye a little eccentricity in the pulleys,
haven't put a gauge on them, belt tension / speed changing is a neat
system where the motor is on an eccentric cam, a la ducati swingarm.
belt itself, an A29, is definitely worn, I'm wondering if it may
have roller chain like stretched sections symptoms.
3/ Spindle head bearing is fairly accessible, and upon removal of
carrier cap (which you need to pull to change the belt) it is again
smooth with no play or cogging.
4/ spindle lower bearings are more or less inaccessible for the casual
service, but can again feel no evidence of slop or cogging.
5/ rattle is related to spindle, and therefore belt speed, and belt
tension, but not related to spindle torque to any noticeable extent,
as guessed from cutter feeds and speeds / rate of material removal.
I know some instances of single phase motors can themselves give rise
to "cogging" as the poles cut through the fields, but to the best of
my knowledge this is usually eliminated as soon as you put some torque
on the cutter and start making chips, not the case here.
I reckon the belt needs replacing anyway, but wondering if anyone had
any relevant experiences or input about the observed phenomenon.
Toying with the idea (as the eventual aim is to CNC the machine) of
fitting an inverter /
speed control / 3 phase motor, but that is some
way off.
Reply to
Guy Fawkes
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It is not unusual in a machine that might have sat idle for some time for the belt to become distorted. If you take it off, does it naturally take on a circular shape? Belts are very cheap to replace and well worth trying first anyway. Variable speed three phase will be well worth it in the long run for the convenience alone let alone smoother running. I use variable speed DC on my mill - just as i had a motor and contoller pair and I'd not go back to single speed now.
Reply to
Bob Minchin
For those that are interested....
Went out and bought a new drive belt, made a point of buying a pukka quality belt (the joins where the belt is made should be all but invisible to eye and finger) and instant transformation, just a very muted hum now, loudest thing is the cutter making chips.
Reply to
Guy Fawkes
It is nice when the cheapest and first thing one tries turns out to be the solution. Why don't I always get that lucky!!
Happy chips
Reply to
Bob Minchin

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