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

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.

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! :eek: 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.

I had some initial resonance points where I could feel some vibration. I think that some may be normal, but a lot is abnormal.
I initially leveled my lathe but there is another thing that I did. That was to make sure that the weight or force on each leg is roughly equal.
Here's how I did it. I raised the tailstock end off the ground from the top surface (engine hoist is best) and leveled the headstock end. So my lathe essentially had a 3 point stance - the definition of a plane. Then I l used a shim between the floor and the tailstock pads as a gauge to confirm that the tailstock pads were equidistant to the floor. Then I lowered the lathe. It helped a moderate amount. Lathe level and roughly equal weight on each leg.

Part 2 - - the next thing I did had more to do with off-balance pieces. I put a shelf across the lower portion of the legs and loaded it down with perhaps 300 or so pounds of sand. That also helped.

If your belt is irregular in some manner it could also be part of the problem. Irregular could mean mis-manufactured (like a lump or irregular thickness) or something as simple as not being lined up or being loose. Double check the alignment, remove the belt and examine it and try a different tension to see if it changes anything. Similarly, if the upper pulley (connected directly to the spindle) was mismachined and/or had runout, I think that it could also manifest itself with some resonance points.
When I first got my lathe it had some resonance points but having leveled it, balanced it, and weighted it, I don't notice them any more. Perhaps some minor irregularities of the belt, pulleys or something has broken in. Or I just am not paying attention to them any more.

[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.
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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! ;)

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Originally Posted by Roger Chandler

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! ;)

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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.

Quote:

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Originally Posted by David C. Roseman

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.

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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!

You might try with the headstock in the middle of the bed and then at the opposite end. Also try lifting each leg slightly with a large screwdriver while it is operating in the speed range of vibration. If you notice any change in amplitude, stop the lathe and place a putty knife blade under that foot. Restart the lathe and see if there is an improvement. If you are trying to take a slight natural twist out of the bed with the precision level process, that can contribute to the problem.

I have a PM3520B that has always (4+ years) had the vibration in that same high speed range. The motor, VFD, spindle bearings and belt have been changed for other reasons and the vibration remains.

Oh, a random thought or two:

One time I thought that I had a bad bearing knock. It turned out that I didn't have the headstock locked down. Embarrassing.

Dustin, I think that Joe had a good idea in regards to figuring out what is moving/vibrating. Besides checking the legs, like Joe mentioned, When you are feeling the vibration, put your finger along the seam between the headstock and lathe bed. Check if you can feel any movement, even if very slight between the two pieces.

Another thing to check might be the bearings. Put a dial indicator on the end of the spindle and tug the spindle to check if there is any looseness or conversely, rotate it by had to check if there is any "lumpiness" in the bearings.

I have contacted Grizzly twice now about the issue and am still waiting to hear back.

The spindle turns easily and freely through its rotation. It has no runout and has no play moving forward and back.

I cleaned the underside of the headstock and after clamping it to the bed went along the entire area where the headstock and bed contact with a .0015 feeler gauge and could not slide it in anywhere.

I have tried moving the headstock to the far left and right on the bed and the middle and the issue does not change. This tells me that it is NOT a platform issue, since moving the headstock will considerably change the weight on each leg.

This morning I pulled the motor out and while holding it in my arms with the belt on its pulley and the spindle pulley I had my wife slowly turn the rpm up to the problem range. The vibration was not as much but was still there. That would eliminate the motor and its pulley from being the issue, so it must be either the headstock itself, the spindle, or its pulley.

Not sure if I mentioned this, but I put the grizzly faceplate on the spindle, and also tried my large cast iron oneway faceplate, and brought it up to the problem rpm range and the range not only was a little wider, but was considerably worse.

After calling Grizzly a FOURTH time, I was told that the machine is within specification and that the vibration occurring is caused from the VFD.

I can send the machine it at my own expense and have it tested...

This is ridiculous.

I would find it hard to believe that a variance in the drive would cause any felt vibration, I would change out the bearings just cause sometimes they can fool you on what you would normally think. Mine had new koyo bearings made in Japan grizzly sent replacements that were made in China I installed them and it has been great since.

I just had a thought if the pot was not good it might made the drive search causing it to pulse and that would cause a perceived shake

Could you see if someone near you has a 766 that you could try? maybe put your head stock on their lathe and use their motor to see if it is the problem.

When I first got my Griz 0766 it had some vibration. Not a lot but enough so I would adjust the speed control to either be above or below the resonance point.

Now my Griz is over 2 years old. It seems to be a lot smoother. I'm wondering if perhaps there is something like the drive belt having some stiffness, or being oval when relaxed, or something that has changed over time.

Just a thought....

Are there others who think that seem to think that their 0766 got smoother over time?