PM3520B Detension belt?

[Ron Solfest]

I've gotten into the habit of detensioning the belt on my lathe.

Why? Because I had a 'ticking' develop a couple months after getting this lathe, after lots of troubleshooting (on this forum etc) I traced the ticking back to the motor (ruled out LOTs of other suggestions, not worth pursuing again). PM sent out a service tech who also traced it to the motor. They replaced the motor and good to go...right? Wrong, after a short while the ticking started again. Again associated with the position of the motor shaft etc.

Long story short, the ticking is worse with more belt tension. I've notice by untensioning the belt when not in use, and being careful not to apply excessive tension when in use, that the ticking has gone away.

Do other PM users untension their belt?

 

[nicktodd]

PM3520B Detension belt

Ron,
I only use the weight of the motor as tension, then tighten the tension handle. I keep that tension until the next time I change speed range.

The only ticking noise my lathe developed was when keeper on the spindle managed to over tighten itself. Other than that, I had no noise issues since 2003.

 

[Mike Peace]

I do same as Nick. No problems in the 3 years I have owned it.

 

[Dwight Bullock]

PM 2530B Knock

Ron,
My PM is not yet three years old and it has developed that same knocking noise. I have tried playing with the tension, but I use no more tension now than when it was new. I am going to replace the bearings to see if that is the cure. I will post again when that is completed.
Dwight

 

[john lucas]

My 3520 A is about 7 years old and I never detension the belt. Heck I hardly every change pulleys so it just stays in the high speed setting. So for no problems whatsoever.

 

[Nate Hawkes]

Guys, this sounds exactly like my 3520B ticking issue. The ticking got worse with tension, but would never completely go away with loosening of the belt. I checked the ticking between the high and low speed settings, and found that on high the clicking doubled in speed.
I thought that I'd done damage to the bearings from all the large unbalanced natural edge bowls I turn. What I found when searching for something loose inside (with the machine unplugged of course!!!), was that the hex screws that held the magnetic RPM readout sensor had come loose, allowing it to jiggle slightly with every revolution, causing the ticking.
This is a VERY odd angle to get your hands, as well as a hex key into, and MUST be done with a short hex wrench; completely impossible with a long one, in my experience. Also, the tricky part for me is that I couldn't position myself to see the screw while my hand was twisted up inside the headstock. You have to see the screw, then go completely by feel.
Since my shop isn't sealed well, and we have them in my area, I did as good a look as possible for Black Widow spiders. Aussies have the close cousin, the redback spider. I found none in the lathe, but THREE in other parts of the shop last year.
Furthermore, the ticking came back a few months later, and was the same source. For whatever reason, it didn't hold the first time I re-tightened it. I'm not a huge guy, but I felt like it was pretty solid. --seems like this could be easily solved with some thread locking compound at the factory!!



If you are sure it is the motor, and not the spindle itself, perhaps the pulley lock screw is just a tiny bit loose? Also, it sounds silly and is unlikely, but have you checked the cooling fan blades to see if one is slightly out of alignment and touching the fan shroud?

 

[Bill Boehme]

In all likelihood, the ticking sound is much more of a nuisance than a real problem, but I am sure it it would bother me too if my lathe made a similar sound.

I think that the suggestion made by Nate is a very likely candidate for the root cause of the problem. However, since we all like to obsess over potential problems with our lathes, here are a few other things to mull over:

• I don't have a 3520, but I seem to recall that it has a C-face motor. As a general rule for C-face motors, manufacturers recommend that they be operated with minimal overhung loads -- never mind the fact that the recommendation is almost universally disregarded.
• Also, if memory serves me correctly, the stepped pulley on the motor shaft is a rather long distance from the motor face which would further increase the magnitude of the overhung load.
• Overhung loads can shorten the life of motor bearings considerably and especially if the belt tension is set abnormally high. A properly tensioned poly-V belt should feel almost loose when testing for belt tension.
• There is no reason to remove the tension from a power transmission belt. Doing so even opens up the possibility of occasionally improperly tensioning the belt. Perhaps the practice of removing the belt tension comes from the unrelated practice of relaxing the blade tension on bandsaws.