Question On Aligning The Lathe Spindle And Bed Twist

mksj said:
The stock belt takes a set on the pulleys, you can feel it catch in one spot, this can cause vibration on the machine. Also you may want to try different belt tension, I run mine a little on the looser side. I had better results with Gates Tri-Power notched belt (BX24 and BX25), link belts also seem to work well by many others. The pulleys seem to run very even on my machine, but might check the belt alignment.
Click to expand...

I have been using a Napa belt, part number from zmotorsports write up. During my tests I have tried both tight and slightly looser with slightly loose giving better results. I had to swap the motor as my lathe started out as a single phase unit so alignment was part of the install. The pulleys visually look good when running so if they are off it won't be much.

I can feel the oscillation when touching the controls but when Matt at PM asked for a video I came up with this method for showing the vibration on the video. I used a cup of WD40 placed on the headstock, you can clearly see when the lathe starts to oscillate by the waves to the fluid. During testing I discovered that the vibration resonated at certain motor speeds, very close to the standard 60hz position. You can see in the video that the vibration peaks at 62hz and is gone at 59 and 64hz and also occurs in different gear settings at the same 62hz. In conversations with Jim Dawson, he pointed out the since the vibration wasn't dependent on spindle speed but did occur at certain motor speeds the problem wasn't in the spindle or chuck but was in the motor, belt, pulleys or input shaft/gears. I am hoping it's either the belt or one of the pulleys as that is much easier to correct.

This particular video was done using the 3 jaw chuck from my Enco 12x36 lathe, at the time we were trying to determine if the PM chuck was the problem.

 
Ok, one last thought, try the motor with no belt (but solidly locked with the adjustment bar, and the motor bolts/pulley is not loose) and see if there is a vibration at the stated frequency. This would isolate the problem to a balance issue with the motor/pulley, otherwise there can be a VFD-motor interaction. I would also try a different VFD carrier frequency, try 12Khz or 10Khz, make sure the VFD motor settings are correct, poles, amps, voltage, etc. Make sure that A016 (analog input filter) is set to 31, and that the motor Hz is staying stable. Last but not least, try to auto tune the VFD to your motor.
 
Can't watch the video, when I click play it says "this video is private". What's up with that? JR49
 
So much good information here. We can see that mksj knows a lot about VFD's, he knows more about the settings than anyone else!
 
It just amazes me how the thread goes from leveling a bed to discussing VFD's.

But its all good discussion/listening material.

We may consider moving part of the thread over to the recondition-repair section.
 
mksj said:
Ok, one last thought, try the motor with no belt (but solidly locked with the adjustment bar, and the motor bolts/pulley is not loose) and see if there is a vibration at the stated frequency. This would isolate the problem to a balance issue with the motor/pulley, otherwise there can be a VFD-motor interaction. I would also try a different VFD carrier frequency, try 12Khz or 10Khz, make sure the VFD motor settings are correct, poles, amps, voltage, etc. Make sure that A016 (analog input filter) is set to 31, and that the motor Hz is staying stable. Last but not least, try to auto tune the VFD to your motor.
Click to expand...
4gsr said:
It just amazes me how the thread goes from leveling a bed to discussing VFD's.

But its all good discussion/listening material.

We may consider moving part of the thread over to the recondition-repair section.
Click to expand...

Ken,

This is all linked together. The vibration issue came up when leveling the lathe and working on the "bed twist". Once the alignment was complete it was time to figure out the vibration. I have been working through the possible causes and have narrowed it to the motor/belt/pulley area but still not sure which is the root cause. I had assumed that it would be mechanical in nature but mksj has pointed out the possibility that it could be electrical. I am glad for the input, more things to check and rule out or fix. That was the main reason I posted in the "questions" area. I just want to get this fixed so I can finish the setup and make parts. LOL

mksj,

I might give you a call for more detail on your suggestions if you don't mind. Thanks
 
Hi Dan, just give me a call, you should have me cell number. Try it with the belt off and also check that the Hz readout is rock solid on the VFD, should not be changing at all. Also need to discuss what feet you are using, I assume they are solid metal feet.
 
No problem. I'm glad you were able to correct the all of the issues. A lot of good input and a lot of things brought up in the reply's left. Don't worry, if any of the thread was to move, we would copy and paste the portion about the headstock adjustments to the P-M section and or to the machine restoration section only.
Great job! Ken
 
sanddan said:
Ken,

This is all linked together. The vibration issue came up when leveling the lathe and working on the "bed twist". Once the alignment was complete it was time to figure out the vibration. I have been working through the possible causes and have narrowed it to the motor/belt/pulley area but still not sure which is the root cause. I had assumed that it would be mechanical in nature but mksj has pointed out the possibility that it could be electrical. I am glad for the input, more things to check and rule out or fix. That was the main reason I posted in the "questions" area. I just want to get this fixed so I can finish the setup and make parts. LOL

mksj,

I might give you a call for more detail on your suggestions if you don't mind. Thanks
Click to expand...

I was over at sanddan's shop this morning to take measurements of his lathe in preparation for building a stand for my own PM1340GT that's on order. I can confirm that he does have a vibration issue when the VFD is driving the motor at about 64Hz. The vibration is subtle, and kind of a shimmy more than a consistent rat-tat-tat-tat thing, but it will certainly have a negative impact on surface finish at that Hz setting.

We did some "let's try this and see" kind of diagnostics, and it does not appear to me that the vibration is due to the chuck, backplate, spindle, belt tension or leveling feet. To me it looks like the issue is out of balance sheaves/pulleys on the motor or headstock drive shaft, or some problem with the belt (which is a replacement belt as specified in another thread). I suppose it's possible the VFD is causing the motor to misbehave/stumble/stutter at that frequency, but I kinda doubt it. I suggested he try a link-belt, and/or get replacement sheaves/pulleys on both ends of the belt.

David
 
You must log in or register to reply here.
Back
Top