belt grinder motor question (wobble/vibration)

B

Brian Baley

Joined
Jun 12, 2018
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11
Hi all,
I am trying to make a 2x72 belt grinder, and have run into a problem.
I am getting significant wobble/vibration at certain frequencies.

To preface, the parts are as follows;
1) wheel kit from Oregon Blade maker - https://originblademaker.com/product/belt-grinder-2x72-wheel-set-24mm-bore-nylon/

2) Baldor 31115 motor (new) 3 phase, 1HP

3) Teco/Westinghouse L510 120v single phase to 240v 3-phase converter/VFD

I spent significant time messing with the alignment of all the wheels in the same plane, and especially the idler wheel on spring loaded riser - but nothing seemed to shake to vibrations.

I turned the drive wheel which was significantly out of round on my lathe, with little or no effect.

I measured the motor shaft run-out using a mag mount 0.005" mic, and there is definitely a 0.005 "hump" detectable in the shaft.

I also am getting pretty noticeable side-side belt wobble - which seems to always be present regardless of which belt (tried 5 of them)

So I am curious as to your suggested steps to troubleshoot and identify the real problem here.

My first inclination is to order a new motor due to the measured run-out and that messing with all the other wheels and everything seemingly in plane hasn't worked. But that is obviously a very expensive proposition.

Hoping someone has some ideas or at least a confirmation that I should give up on that motor.
is 1/2 thou on a 5/8" shaft a lot ?
 
I doubt the motor shaft is the culprit, especially on a new Baldor. You say it's only at certain frequencies? Which frequencies? Some VFD's will vibrate at lower rpm/freq due to some kind of compensation error, but normally this goes away at higher rpm.

Run out should really be measured with a dial indicator. A mic may tell you your shaft is round to within .00001", but if your shaft is bent at a 30 degree angle, it's gonna have miles of runout. That said, I wouldn't worry about .0005" at all. In fact, I'd worry about wheel balance more than runout, more often than not. You might check runout on the wheel too, both outside periphery, as well as on the face of the wheel.

Belt wobble could be a couple of things. Most often it's either one or two of your wheels out of alignment, crowns from drive and tracking fighting eachother, or simply just lack of belt tension. Make your abrasive belt as tight as you can get it and see if it goes away. If not, it's likely an alignment issue, though it could also be a stretched belt (probably not if you tried 5 new belts).
 
knife to a gunfight said:
I doubt the motor shaft is the culprit, especially on a new Baldor. You say it's only at certain frequencies? Which frequencies? Some VFD's will vibrate at lower rpm/freq due to some kind of compensation error, but normally this goes away at higher rpm.

Run out should really be measured with a dial indicator. A mic may tell you your shaft is round to within .00001", but if your shaft is bent at a 30 degree angle, it's gonna have miles of runout. That said, I wouldn't worry about .0005" at all. In fact, I'd worry about wheel balance more than runout, more often than not. You might check runout on the wheel too, both outside periphery, as well as on the face of the wheel.

Belt wobble could be a couple of things. Most often it's either one or two of your wheels out of alignment, crowns from drive and tracking fighting each other, or simply just lack of belt tension. Make your abrasive belt as tight as you can get it and see if it goes away. If not, it's likely an alignment issue, though it could also be a stretched belt (probably not if you tried 5 new belts).
Click to expand...

I should say it is most noticeable at certain frequencies - I'll have to check/verify the actual, but I suspect it's there all the time and harmonics, etc. just make it most notable at a certain point.
I have tried a few springs for belt tension/pressure the current one is quite high (not sure how many lbs)

The drive wheel runout is what caused me to turn it on the lathe, including facing it - to true it up into round and balance in case side/side out which it was a little.

As they came the drive wheel and the idler wheel were both crowned. after turning I retained some crown on the drive wheel but less than as it came to me. I did not touch the idler as it seemed pretty good.

I will see if I can increase the belt tension but it seems pretty stiff/high, and continue to fuss with the alignment of all wheels
do you have any recommended procedures for checking/measuring wheel alignment ?

thanks for your help and ideas, much appreciated
 
Brian Baley said:
belt (tried 5 of them)
Click to expand...
I've had this sort of vibration problem from crap belts.
Try a high quality belt from an automotive supplier etc.
This was on either my basic belt sander (not for knives; just a little basic job) and or it was on my small cut off bandsaw). It has been about twenty five years so not sure which.
also
I was getting some weirdness from the wobbling end of the motor shaft on the cut off bandsaw. I bought the floor model because it was what they had left. I took it home; end of shaft wobbled. I was able to straighten the shaft. I did use a dial indicator to check it as was recommended.

I seem to recall the way I straightened it was a combination of putting a heavy wall pipe over the shaft as a lever and I think I also whamped it a couple of times with a big brass hammer. Not the best for the bearings but I never had any trouble with the bearings afterward. I had a pretty significantly bent motor shaft. I was surprised at how well it straightened up though. Steel has a bit of a memory and wants to go back to the shape it originally was formed.
 
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More often than not when people run into these lurching frequency problems its with a 3450 rpm motor. Mind if I ask if it's a 2 or 4 pole(3600,1800)?
A half thousands shaft diameter variation won't mean anything on a 4 or 5" drive wheel.
I recommend reading through the vfd manual and doing some adjusting for constant torque and speed settings.
If you have reverse you can give a true test for wheel alignment. Run it in forward and track the belt to center of all wheels. If you can't get it centered on all wheels in forward wheels need to be moved in and out. Once it's centered going forward run it in reverse. If it doesn't maintain center in reverse there is a wheel out of angular alignment. Most likely the drive wheel if you don't have a face mount motor. But the tracking or one or both platen wheels can also be misaligned. It's going to take some tweaking and time to get wheels all aligned. With those wheels you will get quick wear if good alignment is not achieved.
 
Brian Baley said:
do you have any recommended procedures for checking/measuring wheel alignment ?
Click to expand...
A long, accurate straight edge held to the side of one wheel to see if the other wheel is parallel to the straight edge. Can add an accurate shim between straight edge and wheel if one wheel is wider than the other and or just eyeball it.

>>>>> link
 
On the L510, parameters 11.08 to 11.10 give “skip” frequencies. 11.11 gives the skip bandwidth. If your problem is at specific frequencies, you can set these parameters to avoid those frequencies.
 
I typically use a straight edge, compensating for differing widths, of course, and just try to square everything up as good as I can.
 
Wowbagger said:
A long, accurate straight edge held to the side of one wheel to see if the other wheel is parallel to the straight edge. Can add an accurate shim between straight edge and wheel if one wheel is wider than the other and or just eyeball it.
>>>>> link
Click to expand...

a 36" "pretty darn flat/accurate" straightedge (not Starret, not certified, not perfect) is what I have been using so far - based off of the drive wheel since it has the largest diameter and the sides of the wheel have been faced on the lathe to accommodate doing this
 
timgunn1962 said:
On the L510, parameters 11.08 to 11.10 give “skip” frequencies. 11.11 gives the skip bandwidth. If your problem is at specific frequencies, you can set these parameters to avoid those frequencies.
Click to expand...

I am not convinced it really is specific frequency ranges - and thinking that it is just really much more noticeable at them
that's a guess so far
 
mike-E said:
More often than not when people run into these lurching frequency problems its with a 3450 rpm motor. Mind if I ask if it's a 2 or 4 pole(3600,1800)?
A half thousands shaft diameter variation won't mean anything on a 4 or 5" drive wheel.
I recommend reading through the vfd manual and doing some adjusting for constant torque and speed settings.
If you have reverse you can give a true test for wheel alignment. Run it in forward and track the belt to center of all wheels. If you can't get it centered on all wheels in forward wheels need to be moved in and out. Once it's centered going forward run it in reverse. If it doesn't maintain center in reverse there is a wheel out of angular alignment. Most likely the drive wheel if you don't have a face mount motor. But the tracking or one or both platen wheels can also be misaligned. It's going to take some tweaking and time to get wheels all aligned. With those wheels you will get quick wear if good alignment is not achieved.
Click to expand...

yes the motor is reversible and i can reverse with the VFD. I will try that
 
I have the same VFD and HAD the same problem. Thought it was bad motor bearing but talked to TECO and there was a setting on the VFD that had to be changed. I had a vibration under 60hz and their fix was:

Change Parameter 1-14 to 0

To change this: Press mode key so that you see parameter setting display 00-00, set the parameter group to 01-00 by using enter to select the digit to change and the arrow keys to select the value. Set the parameter address to 14 using the enter and arrow keys. Hold enter to access the value. you should see the initial setting of 7. Use the arrows to change this to 0 then hold enter to apply this value. Press mode to exit the programming mode

This fixed my issue! hope it helps.
 
Maineiac - I finally got back to this project, and holy cow - this setting you presented took care of 75% of the wobble/vibration!
Not sure how or why, but very interesting and useful !
 
Sounds great! are you running the motor with a drive wheel or pully on it? try it with nothing on the shaft..
 
For just lining up wheels a "certified" straight edge seems like overkill ?
 
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