Spindle vibration on a BP clone with VFD speed control

[Overland]

Just finished conversion of a Seiki BP clone by adding new Baldor 3 hp Vector duty motor, new Woods single A belt taper lock pulleys, new belt.
The machine ran fine with the old Reeves pulley system, until the belt crapped out, so I took the opportunity to rebuild the drive system
I have a fairly strong vibration 60 to 65 motor Hz, about 1700 to 1800 motor rpm.
I have the spindle speed at 45% of motor speed, with the pulleys I'm using. (3.8" motor, 8.2" spindle).
No vibration from 0 motor rpm, until I turn it up to about 60 Hz, then stops at 65 Hz and is fine all the way up to 150 Hz (4,400 motor rpm, about 2,000 spindle rpm).
The pulleys and belt look like they're running true.
I believe the cast iron pulleys are balanced from the factory.
The taper lock bushings aren't perfect due to the saw cut, but small dia, so maybe not much effect.
My thoughts are to remove the larger pulley (8" dia cast iron single groove pulley) and index it on the taper lock bushing to find a "sweet spot". Could be a tedious process.
I doubt the motor is the issue, as it's a brand new Baldor, rated up to 6,000 rpm.
I guess I could try it in back gear, to possibly eliminate the spindle.
Any other suggestions or experience to share please, please ?
Bob

 

[steve-l]

The problem may not be mechanical. It could be the VFD. If you have access to an O scope, I would take a look.

 

[dgfoster]

My approach:

To satisfy yourself that it is not the motor and motor pulley should be easy. Just remove the belt and run the motor speed up and down the scale. It is very unlikely to be the motor, but easy to check the two together. If you get vibration, temove the motor pulley to see if there is still vibration. That takes care of 2 of the 3 elements

Then remove the 8" pulley and install a different driven pulley even if somewhat different size than the one you want to use. Put on a belt and run that combination. If you have vibration at similar SPINDLE speeds, there may be an issue with the spindle---that seems unlikely given the fact that it ran OK prior to install of the new pulleys and drive. But, I'd check.

If the problem is now identified as being the 8" pulley, Learn about checking pulley balance on a knife-edge setup and balance it better by drilling balancing divots on the periphery. Spin it on your lathe prior to reinstall to be sure you have it right.

One other thought is that it is possible that the belt itself could contribute to vibration. You are using a common Vee-belt or a serpentine (better)? My muill and most runs fine on a common vee-belt.

Finally, I have used free phone apps that uses the phone touching a machine to detect and analyze vibration. By knowing the motor RPM and the vibration frequency, you may be able to determine which element of the system is vibrating given the driven pulley and spindle are rotating at a different RPM than the motor.

Denis

 

[rons]

From 60 to 65 Hz...

I don't know if the VFD is a economy style import that is not in first class shape. No offense.

First, I would change the VFD carrier frequency. I'm sure your VFD manual has something to say about what the adjustment range is.
If that vibration zone moves in any direction you know it's related to drive carrier frequency.
Use a mid range carrier frequency like 8 KHz, then 4 KHz, and then 12 KHz. If something changes then maybe the vibration zone is not
entirely due to mechanical components. To tell you my opinion, I don't know what's worse. Maybe mechanical is worse due to cost/replacement.

You may try changing the VFD feedback loop from sensor-less to PID, or whatever. See if anything changes.

Second, I would not even go above 60Hz. Would be happy with what I've got and change the pulley ratio.

I don't trust those half shoe box size drives. I don't trust any VFD...

 

[dgfoster]

Love my four VFD’s. I’d never go back to Reeves drives or step pulleys. The VFD’s with soft start, ramp up and down reverse, and RPM tuning on the fly are a big upgrade for any 3-phase machine IMHO.

I prefer well-documented VFD’s for ease of setup. But even the cheap import works fine after some work setting it up.

Denis

 

[rons]

I have the spindle speed at 45% of motor speed, with the pulleys I'm using. (3.8" motor, 8.2" spindle).

Is 45% a design number?

 

[Clive603]

Is 45% a design number?

Yes if you are optimising set up for lower speed torque and don't really intend to run the spindle over about 2,000 rpm, except for the odd rare occasion when nowt else will do.

My still born conversion was going to use two belt drive speeds to help torque hold up through the range. But iw as going to keep the standard motor. Turned out the major virations and rattles were aver simple mechanical fix so the standard Varispeed drive stayed on. I'm out the cost of the VFD but that will come in one day.

Clive

 

[abarnsley]

I trust Reeves drives to wear, turn hp into waste heat, rattle, use costly belts, and require far more service, than a VFD.

At 3 hp level, cost of VFD is not a big issue.. 2 or 3 Reeves belts...

Modern train locomotives, have been using VFD's for quite a while now..

I don't trust unbalanced taperloc pulleys at highish rpm...

Or L series cheap belts.

 

[Overland]

Thanks to all for ideas.
Fuji VFD, good quality I believe. (Only about $230, so why mess with Chinese junk).
I ran the VFD on the old set up with Reeves, and didn't see this issue.
Good quality Gates belt.
Running this ratio, spindle 45% of motor, to give me a good speed for 3" index tip face mill at 60 Hz.
Just been running the mill doing 1/2" slot at about 50 Hz, about 700 spindle rpm. So QUIET, it's a big improvement !!
I'll check the 8" pulley again, but in the meantime maybe I'll just avoid 60 to 65 Hz.
Thanks
Bob

 

[Overland]

Clive,
I read an old post from "Adama" or similar name, from the UK, from about 4 years ago.
It was his post that got me going on this conversion. Sadly I understand he's passed now, but thanks to him anyway !

 

[gustafson]

Thanks to all for ideas.
Fuji VFD, good quality I believe. (Only about $230, so why mess with Chinese junk).
I ran the VFD on the old set up with Reeves, and didn't see this issue.
Good quality Gates belt.
Running this ratio, spindle 45% of motor, to give me a good speed for 3" index tip face mill at 60 Hz.
Just been running the mill doing 1/2" slot at about 50 Hz, about 700 spindle rpm. So QUIET, it's a big improvement !!
I'll check the 8" pulley again, but in the meantime maybe I'll just avoid 60 to 65 Hz.
Thanks
Bob

what style of belt?

 

[Overland]

It's an "A" section belt.

Well the problem has gone away ????

When I first saw the problem there was a 3" facemill in the mill, from when I last used the machine, before I added new motor, pulleys, etc.

I did a job on the mill today with a 1/2" endmill, than another job with the 3" facemill.

All is fine, no vibration. All I've done is switched out the cutters and tipped over the head a few degrees.

The mill runs very nicely, although a little "knocking" in the spindle until a few tips engage with the cut. I'd probably never have heard this with the old setup !

So all seems good thanks, maybe until I tilt the head back upright........

Thanks for the suggestions.
Bob

 

[dgfoster]

​

Face milling as we speak with my VFD-driven BP J-head.

I also have noticed the hammering sound as entering a heavy-ish cut. I don’t know exactly what causes that sound. Perhaps someone who knows will chime in. But I have learned that if I caused some braking of the mill that reduces or illuminates the sound as I enter the cut. I do the braking with a stick of 1x2 wood pushed against the flat part of the face mill with the far end of the stick supported by the table so as to cause some friction and therefore not allowing it to bounce back-and-forth in and out of the gear engagement if that makes any sense.

If anyone has any other good solutions to this problem I’d like to know about it. I suspect that the clattering noise is the gear is caused by the gearing in the back gear.

Denis

 

[Joe Gwinn]

View attachment 341097Face milling as we speak with my VFD-driven BP J-head.

I also have noticed the hammering sound as entering a heavy-ish cut. I don’t know exactly what causes that sound. Perhaps someone who knows will chime in. But I have learned that if I caused some braking of the mill that reduces or [eliminates] the sound as I enter the cut. I do the braking with a stick of 1x2 wood pushed against the flat part of the face mill with the far end of the stick supported by the table so as to cause some friction and therefore not allowing it to bounce back-and-forth in and out of the gear engagement if that makes any sense.

If anyone has any other good solutions to this problem I’d like to know about it. I suspect that the clattering noise is the gear is caused by the gearing in the back gear.

Are the faces of the facemill inserts hitting the edge square on, or nearly so? I'd use the VFD to slow it down enough to be seen clearly.

 

[dgfoster]

Are the faces of the facemill inserts hitting the edge square on, or nearly so? I'd use the VFD to slow it down enough to be seen clearly.

The noisy cut occurs when facing a more or less triangular casting that is about 2.5” on a side. So, entering the cut the inserts do, unavoidably, strike the edge more or less straight on. Once the cut has advanced enough for two teeth to be in the cut, the hammering diminishes and smoothes out completely once well into the cut. I am using a 3,5” diameter face mill with Iscar APKT 1604 inserts optimized for cast iron. These inserts cut very well and are remarkably durable, but I’d like to avoid the hammering. In the pictured cut I am taking above, there are plenty of teeth engaged and the cut is smooth and quiet.

Easing into the triangular face helps as does reducing depth of cut. Still I worry that the hammering may be damaging the back gear or the bevel gears in the BP right angle head used on the triangle cut.

Denis

 

[Overland]

Following your comments Dennis, I looked at my machine again this morning.
If I "rock" the spindle back and fore there is a small amount of movement, and the knocking sound. This is in high gear. So I'm guessing there is a little clearance/play in the splines, which probably where the sound is coming from.
Bob

 

[dgfoster]

Following your comments Dennis, I looked at my machine again this morning.
If I "rock" the spindle back and fore there is a small amount of movement, and the knocking sound. This is in high gear. So I'm guessing there is a little clearance/play in the splines, which probably where the sound is coming from.
Bob

Ill check that on my machine too. I like that source better than a clattering gear train.

Here is the casting with the “triangular” face that I have to cut. No matter how I orient it I have to either enter or exit cutting just an apex. So at that point there is only momentary single-tooth engagement.



Denis

 

[gustafson]

Two sources of knock I am aware of

spline knock, work it long enough hard enough it willhappen

My buddies machine has a similar knock that shuts up if you lean on the hi/low lever, not sure the physics of it, but there it is

Vari heads will rattle from the pulley bushings but that is different

 

[abarnsley]

Spline play is part of it.

But the dog clutches on spindle pulley hub, and splined gear hub, are the major noise source..

Hi low lever or cam ring movement, can allow dog clutch teeth to engage slightly more or less.

The dog teeth are cut at a slight angle. A little tooth end clearance gets magnified.

Supposed to drop down.. hit angles, lock up tight and rattle free..

Fix is new parts.. Even if spline play only, is the issue... Same part/s required to fix...

Backgear unit is pretty solid (for it's size) Usually not a major rattle battle there..

Noisy operation at certain speeds can be expected..

Especially if run at speeds not reachable before VFD's..

 

[GregSY]

I wonder what the pole count of the motor is? I hope it's a 4 pole....

Running at 60HZ and having problems is 'not acceptable', for sure.

It's kinda funny....since the rise of cheap VFDs all sorts of problems with vibrations and harmonics have sprung up...among small motor users. All of these problems have existed for decades and millions of dollars spent on solutions, studies, and fixes - among large equipment users. Terms like critical speed, separation margin, and dead band come to mind.

But if you're looking to run 0-6000RPM without issue, with system that is a herky-jerky compilation of belts, sheaves, motors, and other stuff....keep your fingers crossed.

Balance is a relative term....everything might be in balance at one RPM and not another RPM. Also, everything might be in balance individually but as a system...out of balance.