Importance of Belt Tension

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parshal

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I've made a number of things on my 1340GT since getting it up and running last week. I bought a BX27 belt and flipped the pulleys and am running the two large pulleys with Mark's VFD setup. I read in the owner's manual to not use gravity on the motor to set the belt tension so I loosened it a bit a few days ago. After getting the tach set up I was playing with the gears and running the speed pot to see how fast it would go. When I started it in high I got a high squeal and found it to be the belt so I went ahead and tightened it using the weight of the motor. Well, today I found I had a lot of vibration. So much so the chip pan would shake. I used the speed pot to work around the vibration. Since that was a new problem, I loosened the belt and all vibration is now gone. Zero. The belt is quite loose. I'd never have thought about running it that loose but it works well.

Something to think about if you guys get vibration.
 
I am not sure if this works for machine tools (don't know why it wouldn't) but linked belts are used extensively on woodworking equipment to reduce or eliminate vibration. Link belt here at this Linky
 
Use of linked belts does help in some cases, but technically they are not bidirectional per the manufactures recommendation. They were originally designed as temporary belts. Harmonics and vibration nodes can be more of a problem with VFDs because there is always some harmonic frequency point for every system, one reason why VFDs are designed with skip frequency bands so one can bypasses those frequency ranges. The 1340GT always seemed to be a bit more sustainable to some excitation frequency, partly because it is "relatively" light weight wise, sits on a tall cabinet, and has a high center of gravity. Small weight imbalances in the chuck can also cause problems. Belt tension is just one factor in the equation, along with better quality belts (that are more uniform in dimensions and less likely to take a set) that individuals need to evaluated. Tighter is not always better, but I also reacall a 1440GT owner complaining the spindle speed was dropping when he was cutting, and his belts were too loose. So the porridge needs to be just right, not too hot and not too cold.
 
I checked the 1340GT manual and it didn’t have what my manual has....see below...1440GS

288856
 
Mine has an inch or so of deflection. 1/4" is about where I had all the vibration.
 
I tend to run any belt on pulleys as loose as I can run without any slippage. I Don t think people realize the mechanical advantage of tension setting the belt. Too tight and your putting stress on your bearings.
 
MarkM said:
I tend to run any belt on pulleys as loose as I can run without any slippage. I Don t think people realize the mechanical advantage of tension setting the belt. Too tight and your putting stress on your bearings.
Click to expand...

:agreed: The Chances are that Eventually the belts will get glazed over on the working surface which will lead to slippage usually accompanied by a very annoying squeal! When this happens its much better to deal with that "glazing" by going over them with some fine grit sandpaper or Emery cloth to break up the glazing or by changing out the belts Instead of over tightening them in an effort to stop the slippage!
 
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Not a lathe, but my homebrew CNC spindle runs 2.5HP through a GT3 timing belt arrangement. Timing belts are normally louder than V belts and this one runs at 5000rpm. I finally got the noise to a near wisper by loosening the belts until the was no slop but no tighter. I was as surprised as you.
 
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