Pros and cons of a double belt arrangement for a 1340gt?

Parshal is that with a link or the Gates belt?

Now here is another development in this saga. While all this testing belts has been going on I discovered source of vibration may not be the belt at all but the motor! I need to pull the pulley back off to see if that's where it is coming from but with the belt off there is a really noticeable vibration coming from the motor and may be what I've been chasing all along. With the belt on and driving the head it dampens it some but it's there. Gets worse the faster I run the motor and at some harmonics of the machine, it's really bad. I was thinking that was coming from the belt. Now I'm going to have to track this down. I can work around it but it really bugs me. I can run in a higher gear in the head and slow the motor with the VFD for the same cutting speed and it's tolerable. But I shouldn't have to do that. I debated upgrading the motor to a inverter/vector rated motor when I got it. Now I may be taking that plunge. First though, I'll pull that pulley off to rule out it as the problem this weekend. But I'm just suspicious the motor itself has an imbalance in it thats causing this vibration.
 
I thought, too, that it might be the motor for me. But, when I run the motor without the belt have zero vibration. I've noticed a squeak in the headstock pulley but no vibration or anything weird that I can see.

I've tried two different Gates belts and two different link belts and they all do roughly the same thing. If the weight of the motor sets belt tension there's vibration. I need to do some more testing but every time I remove a belt it's a long process of trial and error to get it where it needs to be for vibration free.
 
There is one other factor too look at, the tension adjustment bar for the motor on mine had a bit of play at the mounting screw going into the head stock which could cause the motor not to be held rigidly. Rather then pull the upper head stock pulley to remove the bolt, I used a lock washer that I open enogh to get onto the bolt and then closed it. It stopped the tension adjustment bar from rattling at the top mounting hole.

The motor should be absolutely smooth, if you are getting vibration then something is wrong with it. May be worth replacing with a Marathon motor.
 
Good tip Mark, I did notice the slop in that tension bar. Will do that.

Tested again last night and the motor definitely has a vibration in it. With no pulley, just the motor will vibrate. It gets progressively worse with the VFD above 50hz all the way up to 90hz. At 50hz it's barely noticeable, below I can't feel it. The vibration can be felt by laying my hand on the carriage so I don't like it.

With the pulley on (and no belt) it's worse. I suspect the pulley also has some balance issue that then adds to the motor vibration. I was hoping that was the only thing because I could just balance it or get a better pulley. So for now I am going to run the motor at 50hz or less and just use a higher gear in the head. With the belt back on that seems to be the quietest the machine will run.

At the end of the day I am not sure this all is really affecting anything meaningful but it bugs me. If there is vibration I can feel it's got to be affecting something. I don't get mirror finishes most of the time but I usually blame my lack of experience & choices with materials/speeds/feeds or tooling, weight of machine, etc. I was on the fence about a motor upgrade anyway so it may push me over. I am going back through your threads on that.

As always, really appreciate this forum and the wisdom here.
 
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