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

[dustin wassner]

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...

[Roger Chandler]

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.

[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.

[Bill Jobe]

That problem seems very unusual.

[Roger Chandler]

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.

[Roger Chandler]

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.

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!

[David C. Roseman]

[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]

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!

[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

[Roger Chandler]

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

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!

[David C. Roseman]

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

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

[dustin wassner]

Interesting. When I spoke with a technician at North American and Teco Westinghouse they both stated that the higher carrier frequency would cause the wingdings to run hotter.

Did you adjust the frequency on yours, and if so, how long have you been running it like this?

I will PM you. As a side story, my Teco VFD had an abundance of settings as well. One was deceleration rate. Being impatient, I turned it way down. I then finished truing the 24" mdf disc sander attachment I was making. I had never used the grub screw on a faceplate before... you may see where this is going. Lets just say that a disc that size at 1700 rpm that unthreads off the spindle comes alive when it hits the ground... I now use factory decel rates and grub screws...



I have the lathe on concrete, and although I do not yet have it anchored to the slab, after shimming, the bed is dead level. I used my Starrett machinists level and both ends of the bed are within .001 width-wise, along with levelness along the length. Vibration was still there at the exact same rpm range. However, what I did not notice before, is that the vibration returns around 2k rpm but not as strong, but is worth noting since it is double the lower rpm vibration.

[David C. Roseman]

Dustin, I've emailed the write-up to you. Yes, I adjusted the pulse width modulation carrier frequency on my G0766 two years ago, and on my G0733 four years ago (same series of inverter, but a different model to match the smaller 2 Hp motor on the G0733). No problems whatever since then. I also helped several other G0766 owners do the same about a year ago. The write-up discusses the various considerations involved.

I hear you about shortening the deceleration time too much on a VFD lathe! Sounds like your Teco may have an onboard braking resistor in order for it to stop so suddenly without going into "motor regeneration" and sending voltage back to the DC buss, causing the VFD to trip off for a few minutes to protect itself. On your Grizzly G0766, deceleration time is adjustable by changing the value of pr. 11. But if you want to shorten deceleration time, I recommend you first add a $40 Delta electronic braking resistor, especially if you intend to turn very, very heavy work pieces. If you are impatient about allowing the lathe to stop gradually each time you stop to check your work, you can inadvertently trip the VFD's internal breaker by trying to stop too quickly, e.g., by (1) toggling the directional switch to neutral instead of turning the potentiometer down slowly, or (2) by shortening the deceleration time by changing pr. 11 without adding the additional electronic braking. When the VFD trips off, inertia will cause the spindle to freewheel until it slows down by itself. That would make you more impatient. Adding a breaking resistor is easy, but involves some additional, simple parameter changes. That's covered in the write-up if you decide to do it.

[Roger Chandler]

[QUOTE=David C. Roseman;2762942 Yes, I adjusted the pulse width modulation carrier frequency on my G0766 two years ago, No problems whatever since then. I also helped several other G0766 owners do the same about a year ago.
[/QUOTE]
David.....now you have my interest peaked here. Exactly what does adjusting the pulse width modulation carrier frequency accomplish and what "problems" were you having that the adjustment addressed/eliminated? My G0766 seems fine with the factory settings, but if it could be tweaked even more to up the fine performance to an even higher level, then I'd jump on that!

[David C. Roseman]

David.....now you have my interest peaked here. Exactly what does adjusting the pulse width modulation carrier frequency accomplish and what "problems" were you having that the adjustment addressed/eliminated? My G0766 seems fine with the factory settings, but if it could be tweaked even more to up the fine performance to an even higher level, then I'd jump on that!

Roger, sorry, I should have been a bit clearer. When I said "no problems whatever since then", I meant no problems resulted from restoring the pulse width modulation carrier frequency setting to the Delta Electronic factory default value of 15kHz. The lathe shipped from Grizzly with a pr. 71 setting of 9kHz. The only reason I changed the setting in the first place was to get rid of some acoustic motor noise that presented as a high-pitched trill audible at certain rpms. The adjustment completely eliminated it. The trill doesn't affect performance at all. Many folks wouldn't mind it, and some, including two or three of my many friends who have G0766s, don't even notice it.

[Roger Chandler]

Roger, sorry, I should have been a bit clearer. When I said "no problems whatever since then", I meant no problems resulted from restoring the pulse width modulation carrier frequency setting to the Delta Electronic factory default value of 15kHz. The lathe shipped from Grizzly with a pr. 71 setting of 9kHz. The only reason I changed the setting in the first place was to get rid of some acoustic motor noise that presented as a high-pitched trill audible at certain rpms. The adjustment completely eliminated it. The trill doesn't affect performance at all. Many folks wouldn't mind it, and some, including two or three of my many friends who have G0766s, don't even notice it.

Thank you sir! Not a bad way to go, and I saved that .pdf you sent me on it last year or so ago. I might have to get you to stop by at some point [maybe the Symposium when you are in my neck of the woods] and help me adjust mine. The "trill" doesn't annoy me at all, so I guess it is no more than any of the 3520b's I've turned on, but I do have some hearing loss in the upper frequencies. I can hear it though when I use my lathe, but with the overhead air cleaner running and my Trend Airshield Pro on, the noises from those probably drown it out for the most part. You're a good man David, and thanks for all the help you give both here and on the GGMG!