Grizzly G0766 vibration issue. If you have this lathe, please comment

I just finished setting up the new machine.

I am getting a notable vibration in a very specific rpm range (rather a frequency range) on both the high and low range. Literally, just below 950 rpm and it is smooth as glass, as well as just above 1100. Between these it is terrible. I don't remember the specific rpm range for low speed.

I tried running the motor without the belt and there was no vibration. I am not measuring any runout anywhere, and don't believe this is a matter of something being out of balance.

I think it may be an issue with the 3 phase motor when under load. I built a lathe this past year and had the identical issue, where I would run the motor between 43 and 49 hz and the motor itself would vibrate, almost like the VFD was causing some kind of weird resonant frequency pulsation as it was converting the DC into AC. I know that resonant frequencies deal with sound, but whatever the "resonant frequency" equivalent is for electrical stuff, I think I may be experiencing it. Not really sure, but it seems like way too tight a range to be a mechanical out-of-balance issue...

Either way, has anyone else who owns this machine found this to be an issue?

I plan on contacting grizzly monday. I do hope they can offer assistance...

Make sure youhave gone through the lathe and tightened all the screws, especially the pulley set screws on the spindle and motor shafts. Make sure the clamp plate is seating tight underneath the bed ways.....sometimes as little as a half turn of the nut can make a difference in vibration. Inspect the belt and pulleys to make sure there is not a place on the belt ribs that has a buildup of debris on it.
My G0766 runs smooth as silk, but the first thing I did when uncrating and assembling was to go through the entire lathe and tighten every screw, bolt, nut and get everything dialed in.

There is also a spindle spacer next to the pulleys and it has a step in one side that fits into the side of the pulley, and it needs to be snug into the pulley, and locked down with the set screw, so check that as well.

I just gave the entire thing another once-over. Everything looks great.

I just rechecked the rpm range of vibration. It is exactly the same on both the high and low range, so it is NOT occurring at the same frequency...

I am encouraged that yours runs smooth at all rpm's. I am confident that Grizzly will help me with this.

thanks for the input Roger.

That problem seems very unusual.

I recommend you call Grizzly tech support, and let them walk you thru the issue to troubleshoot......they may decide to send out a new part, or something.

Make sure you have the bed of the lathe level; left to right, front to back. You would be amazed at what happens when the bed has a very slight twist.

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Originally Posted by Steve Schlumpf

Make sure you have the bed of the lathe level; left to right, front to back. You would be amazed at what happens when the bed has a very slight twist.

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I actually thought about the same thing last night right before bed, so I'm glad you mentioned this Steve. Harmonics on a lathe get magnified from the seemingly most insignificant things. Also, what may not show up on a midi lathe or smaller lathe will show up on a larger lathe because it has such a larger frame, and what is just a small amount of twist is magnified much more with a long bed and much more cast iron or steel.

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Originally Posted by dustin wassner

I just gave the entire thing another once-over. Everything looks great.

I just rechecked the rpm range of vibration. It is exactly the same on both the high and low range, so it is NOT occurring at the same frequency...

I am encouraged that yours runs smooth at all rpm's. I am confident that Grizzly will help me with this.

thanks for the input Roger.

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It showing up on both high and low range makes perfect sense, in that the pulleys are cast together, and are not separate individual pulleys. That means that if there is a something in a particular spot on the rotation, then it will show up on either belt setting, however, it would seem it would also show up at any rpm. Make sure that bed is level, as mentioned in my reply to Steve.

Know this, Dustin....that the great majority of issues people have had with the G0766 when they initially got it was due to setup issues. You can read threads on the GGMG, and see where we've dealt with bed leveling and vibrations, etc. Even, the weight distribution on the legs can affect harmonics. If one of your feet pads is not carrying approximately the same load as the other feet, it can make the harmonics do strange things. Most of the time it is something related to the users setup...........that being said,

If there is something about your machine, Grizzly will make it right. Not sure how much experience you have with lathes, but just trying to be helpful here......the Grizzly Green Monster Group [GGMG] was started by me back in 2010 or 2011 just to give owners a place to bounce things off one another and be a support group, and there is a lot of knowledge there about these lathes, so feel free to join! :)

I had the exact same issue when I first set up my G0766, vibration in that same speed range only. Carefully leveling the lathe fixed the problem. Hope it works for you.

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Originally Posted by dustin wassner

[snip}
I just rechecked the rpm range of vibration. It is exactly the same on both the high and low range, so it is NOT occurring at the same frequency...

[snip]

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Dustin, a couple of thoughts in addition to the good advice Roger and others have given.

First, perhaps I'm misunderstanding, but I'm puzzled by your comment about frequency. If the vibration is occurring at the same rpm in both high and low range, then isn't it, in fact, occurring at the same frequency output of the VFD? Changing between high and low range simply changes the gear ratio mechanically by moving the belt. No? The digital readout on the headstock's display shows only rpm. So I gather you mean that the vibration is occurring at the same rpm readout, regardless of the belt being in high or low range.

To see the frequency output, you'd need to pull the steel dust cover on the Delta VFD.

Second, is the vibration that you are noticing accompanied by a change in the sound coming from the motor, specifically a high-pitched trill? Or is it simply a vibration (rapid shake)?

Congratulations on the new lathe!

David,

Thanks for the response. The vibration is occurring at the same rpm range, but to obtain this same range on either the high or low would require a different frequency. The potentiometer knob is in a completely different place to achieve the vibrating rpm in high vs low range.

The motor does make a high pitched noise that changes throughout the frequency range, as did the lathe that I built. I found that on my old lathe, when I changed the carrier frequency in the vfd, it altered this electrical noise, and could be nearly eliminated if I were to max out the carrier frequency, but it would make the motor run hotter.

The vibration, as I can tell, has no correlation to the electrical noise, its just a rapid shake. But the problem is just so darn similar to the one I experienced before that it is hard to believe that it is not similar in cause.

DW

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Originally Posted by dustin wassner

David,

Thanks for the response. The vibration is occurring at the same rpm range, but to obtain this same range on either the high or low would require a different frequency. The potentiometer knob is in a completely different place to achieve the vibrating rpm in high vs low range.

The motor does make a high pitched noise that changes throughout the frequency range, as did the lathe that I built. I found that on my old lathe, when I changed the carrier frequency in the vfd, it altered this electrical noise, and could be nearly eliminated if I were to max out the carrier frequency, but it would make the motor run hotter.

The vibration, as I can tell, has no correlation to the electrical noise, its just a rapid shake. But the problem is just so darn similar to the one I experienced before that it is hard to believe that it is not similar in cause.

DW

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to obtain the same rpm range on different pulleys, it means you would have to change the potentiometer settings. This sounds like something with your setup, and not anything electrical with the lathe to me. That mechanical ratio of the pulleys are different and mean that to get to say 800 rpm on the low belt setting, your pot has to be at a higher place on the speed dial, and much lower on the dial if you use the high belt setting. The inverter/motor hum is normal and mine actually improved as the lathe broke in....some high pitched sound is normal, but vibrations at a certain rpm speed is likely to be something in the harmonics, which is probably in the bed being torqued, and load distribution to the feet not being fairly equal.

Having to reach the same rpm for this vibration to manifest itself whether on high or low belt settings tells us that there is not some issue with the spindle being bent, or some issue with the motor, as it seems to smooth out at higher and lower rpm's. This really does sound like harmonics, and you will have to trace that one down in your individual and unique shop setting. For example, if your floor is concrete and has lower places and higher places [as most concrete floors do] then the weight distribution on the foot pads could be an issue if one is in just a slight depression in the concrete.
You could try putting a small piece of rubber pad underneath each foot, and that may take away those vibrations. If you are on wooden floors, then a particular board, or floor joist may be 1/8" out of level, and that can affect the harmonics of the lathe......every shop is different and every turner needs to dial his setup in, so that it gets the best performance.

I refer you back to Gary's identical issue in his above post........likely you will have the same remedy!;)

I was also going to suggest that having all 4 feet flat and even on the ground is often a culprit with this issue. Concrete floor is a must. Other than that, no real idea.

robo hippy

I looks like that lathe is constructed much like certain Jet and Powermatic lathes.

If so, be be sure you have not over-tightened (or under-tightened) the belt. Many people push down on the lifting lever before locking and some have experienced damage from over-tightening. The PM 3520b instructions warn "do not overtension" and in places recommend to let just the weight of the motor provide the tension. The Jet 1642 manual states "Lower the tensioning handle so that the weightof the motor provides the needed tension and tighten the locking handle."

The 766 instructions say otherwise but they do provide a spec for belt deflection at the proper tension. (uncalibrated, of course)

Just something to check.

Also, for a clue you might use a stethoscope (or a big screwdriver with the handle to the ear) as you would in any machinery to try to pinpoint exactly where a sound/vibration is originating.

JKJ

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Originally Posted by dustin wassner

David,

Thanks for the response. The vibration is occurring at the same rpm range, but to obtain this same range on either the high or low would require a different frequency. The potentiometer knob is in a completely different place to achieve the vibrating rpm in high vs low range.

The motor does make a high pitched noise that changes throughout the frequency range, as did the lathe that I built. I found that on my old lathe, when I changed the carrier frequency in the vfd, it altered this electrical noise, and could be nearly eliminated if I were to max out the carrier frequency, but it would make the motor run hotter.

The vibration, as I can tell, has no correlation to the electrical noise, its just a rapid shake. But the problem is just so darn similar to the one I experienced before that it is hard to believe that it is not similar in cause.

DW

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Thanks, Dustin. Yep, if you're not detecting a correlation between the electronic motor noise and the vibration, then I think we can rule out that vibration is related to a VFD setting. So I agree with Roger and others that it's likely a harmonic vibration originating from a slight mechanical imbalance somewhere.

If, instead, the vibration correlated with that high-pitched, trill-like motor noise that changes with spindle rpm, I was going to suggest checking the pulse width modulation carrier frequency (parameter pr. 71) on the G0766's Delta Electronic VFD-M series motor drive. I've never heard of the pr. 71 setting being related to any vibration issue, but your experience with a similar vibration on your earlier home-built lathe traced to pulse width modulation made me curious about that. BTW, I'm not an electronics engineer, but I don't think you'd need to worry about overheating the motor if you were to max out the pulse width modulation setting by increasing the frequency on that particular drive. In fact, according to a Delta Electronics technical rep I checked with last year, the higher the setting the better the heat dissipation. Pr 71 of that inverter has a user-adjustable range of 1 - 15 (1kHz to 15kHz). The default setting is 15 when the unit leaves the Delta Electronics factory. Of the six G0766s I checked about a year ago, pr. 71 was set at 9, so I concluded that the factory in Asia that builds the G0766 to Grizzly's specs dials is back to 9. The lower the value, the more acoustic motor noise is noticeable, while the higher the value, the more electromagnetic interference may occur. Unless EMI is a particular concern, then dialing the setting back up to the Delta factory default should eliminate the trill if it is bothersome. Some folks find it so, others don't even notice it!

Grizzly locks out the onboard keypad on the VFD-M, presumably to discourage owners from fiddling with any of the 157 adjustable parameter settings and inadvertently creating problems. :) However, the keypad can be unlocked, and parameter changes made even without the keypad, by going in through the drive's telecommunications port with the correct interface and your laptop. The necessary software can be downloaded from Delta's website. Last year I put together a tutorial on this, as well as on adding an electronic braking resistor to the drive (it already has dedicated terminals for a braking resistor). I'll be happy to email you a copy if you'd like. Just PM me with your email address, as the file with pics is too large to post.

I think you're going to love that lathe once you sort out the vibration issue.

David