# Pm 12x36 Vibration Problem



## Nate_L (Jun 19, 2016)

Hello folks -

I've got my new PM 12x36 run in, but I get a lot of vibration with the power on.  The top of the (factory mounted) DRO is swinging maybe 1/4" left to right, as are the lamp and coolant nozzle.  It's fully developed after just a couple seconds of power.  I don't hear anything that seems unusual, but I'm a noob.

The vibration is present even with the whole gearbox out of gear (top left lever between gears).  With the belts off, it's pretty smooth.  The motor isn't moving around with the belts on, but I'd have to defeat the interlock to know more - which I'm not eager to do.

I've read that the factory rubber belts can take a set; they look okay, but I replaced them with new link belts - didn't help.  I haven't experimented with belt tension yet.

I don't see anything that looks crooked or wobbly, inside the gearbox or out.  The motor pulley face, with a DTI on it, varies .005 or so; on the diameter, it varies .002.  The driven pulley is a little closer to true in both directions.

Should I be fighting to get the pulleys dead on, or is there something else I should look at?

I've got the thing pretty well leveled on eight leveling feet, a couple of which are not firmly on the ground afterwards.  I don't yet have the blue plate mounted between the stands, as I thought that might set up some contributing tension (and make the leveling feet harder to reach).

Any advice? Thanks!


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## kd4gij (Jun 19, 2016)

That does not sound good. I would call Mat or who ever runs PM.


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## Muskt (Jun 19, 2016)

I have experienced a very similar problem with mine.  I have been able to get almost all of the vibration eliminated.  Here's how I went about it.

First, I figured that I needed to see what was happening on the motor end with the machine running.   I removed the cover from the gear end of the lathe and CAREFULLY held the safety switch button in while pressing the jog button with the other hand.  I immediately observed a large portion of the problem.  One of the drive belts was very loose when compared to the other and flopped quite a bit while running.  This was on the setting what produced the lowest RPM.  So, I released the buttons and unplugged the machine and then changed both belts to the other speed setting.  After tensioning and aligning the motor, the test/observing procedure was repeated--with slightly better results, but still lots of vibration. Next, I removed one of the belts--the one that appeared the loosest .  With only one belt , very little vibration was present.  I changed the belt back to the low speed setting and repeated with the same "pretty good" results.  I tried the other groove with only the one belt--still pretty good.
So, off to NAPA & purchased 2 Gates belts and back to the shop.  Put them both on and back to the heavy vibrations again.  
Removed one and the vibs nearly gone.
HMMMMMM!!  
Next, I ordered enough of the Link style belt to fab 2 belts--exactly the same vibs.  So removed one and now, it is smoother than ever, but only one belt is installed.
So, I have been using it for just over a year with only the one belt.  Almost all of the vibs are gone except at the 500 RPM setting.  That one setting still produces quite a bit of vibration, but it is usable.
Changing the belt settings, while not terribly difficult, is a giant pain in the butt.
Having your fingers so close to the running belts is scary. 
Aligning the motor pulley to the lathe pulley is fairly difficult because of the location of the motor bolts.
Anyway, I wish you well with your project, just be careful with your fingers when doing it.

Best to you
Jerry in Delaware


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## Bob Korves (Jun 19, 2016)

Sounds like the pulley grooves might not be machined well and/or equally from what Jerry is saying.  Look at the grooves carefully for machining issues, and use an indicator on all four of the pulley tapers where the belts ride.  Talk to Matt as well, right away.  If two of you have had the same problem, it might be a known issue with a standard fix.


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## Firestopper (Jun 20, 2016)

Use a jumper on the safety switch while trouble shooting (keep hands free and clear) ensure ALL your leveling feet are supporting the machine before moving on.


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