Spreadsheet for Balancing

I recently became fascinated with balancing, and have got my old Logan running about as smooth as one could hope for. It isn't very difficult, though little practical information seems to have made its way from old vibration and tool engineering books, to the 'net. I've put up a spreadsheet for single plane balancing, though it's easy to do 2-plane (full dynamic) balancing if one constructs a support fixture for the rotating component.

http://www.conradhoffman.com/chsw.htm

I've just looked through the website; it is most informative, and quite a generous gesture on your behalf.

Thank you for the contribution; especially those balancing constants and equations.

Conrad Hoffman said:

I recently became fascinated with balancing, and have got my old Logan running about as smooth as one could hope for. It isn't very difficult, though little practical information seems to have made its way from old vibration and tool engineering books, to the 'net. I've put up a spreadsheet for single plane balancing, though it's easy to do 2-plane (full dynamic) balancing if one constructs a support fixture for the rotating component.

http://www.conradhoffman.com/chsw.htm

Click to expand...

I quickly looked at your spreadsheet it is more than a product of a fascination. I am just starting to two plane balance a cantilevered blower - why start with the easy work. I imagine that a headstock would also require two plane balancing. I never thought of doing that but I can see the benefit of improving the machined finish.

An Infra-red detector is used to recognize a zero degree spot and the rotor's angular position is determined by dividing the distance between the two pulses into 360 equal parts.

To determine the state of imbalance there are two accelerometers mounted over each bearing on the bearing housing. Well there is a bit of cheating because a third accerometer is mounted at 90 degrees the other two to give better insight about the couple unbalance.

In the first attempt a 1.75 g imbalance was found. A few trial weights were placed and brought it down to under .5 g at 3000 rpm. There were some lower frequencies that were mucking up the readings, I didn't run filters but I suspect that the belt was the contributor. The remedial work has already started.

This week I hope to look more closely at your spread sheet because it appeared to me that it would allow me to convert the g forces to grams if I plugged in the rpm and the weight in grams of the added weight.

You are way ahead of me on this so the purpose for this text is to show that I am interested in your work and look forward to reading about your progress (positive and negative). And you know about the Zone System too!!!

Oh, I do have Victor Wowk's "Machinery Vibration: Balancing". Understanding it is a different matter.

Raymond

Toolpost- Thanks for the kind words!

Raymond- Very cool stuff. I make much of my living as an electronic designer, but naturally had to assume the people wanting to balance things might want nothing to do with that. So far the things I've wanted to balance were big pulleys and such, so single plane has worked well. Usually motors and spindles were well balanced at the factory, or have such a small diameter that they aren't a major problem. The principle of 2-plane balancing, using the traditional pivoted stand, looks straightforward enough, and I plan to build a proper stand. A fancier rig using several accelerometers would be a fun project. One thought that occurred to me is that any computer sound card or built in sound system can handle two channels with plenty of bandwidth for the speeds we're interested in. I think FFT routines are common enough that it would be easy to filter the data and program the equivalent of a multi-thousand dollar system, for peanuts. Anything I've done so far absolutely required filtration to eliminate all sorts of unwanted noise from belts, other shafts and motors. Until now I didn't realize that motors contribute a huge 60 or 120 Hz vibration even when perfectly balanced- 3-phase is apparently far smoother, as should be a VFD. Keep me up on your progress!

Conrad: I haven't digested the balancing spreadsheet, but suspect it will come in handy. However, your website has an explanation for a weston standard cell that is great. I have an old one that appears to be phyiscally OK. Now to get up a bridge to use it. Thanks for the great explanation.

Conrad Hoffman said:

... The principle of 2-plane balancing, using the traditional pivoted stand, looks straightforward enough, and I plan to build a proper stand. A fancier rig using several accelerometers would be a fun project. One thought that occurred to me is that any computer sound card or built in sound system can handle two channels with plenty of bandwidth for the speeds we're interested in. I think FFT routines are common enough that it would be easy to filter the data and program the equivalent of a multi-thousand dollar system, for peanuts. Anything I've done so far absolutely required filtration to eliminate all sorts of unwanted noise from belts, other shafts and motors. Until now I didn't realize that motors contribute a huge 60 or 120 Hz vibration even when perfectly balanced- 3-phase is apparently far smoother, as should be a VFD. Keep me up on your progress!

Click to expand...

I like the approach of using brains instead of throwing money at the problem. Not what I have done but I am willing to learn. I have adapted equipment from previous projects therefore have a200K/sec 4 channel simultaneous DAQ. The preliminary runs had a dominant and easily interpreted signal but it appears that the real challenge will soon begin and more technique than what is available in the Bluffer's Guide to Balancing will be required.

My attempt to balancing is field balancing rather than working in a balancing frame. That way nothing is taken apart and nothing is added to the dynamic components. While balancing the blower is turned by a Perske spindle motor / Yaskawa VFD controller. For the moment it is Jason belt driven.

Currently I am waiting for two back ordered bench type drill presses (from unspecified country) to remove metal since it is not possible to add weights (this is where your generous gift of the spreadsheet is appreciated).

Raymond

kc5ezc said:

Conrad: I haven't digested the balancing spreadsheet, but suspect it will come in handy. However, your website has an explanation for a weston standard cell that is great. I have an old one that appears to be phyiscally OK. Now to get up a bridge to use it. Thanks for the great explanation.

Click to expand...

Ok, I admit it, I'm a metrology freak. Some time back I wrote an article for Electronics Now on building a voltage standard, Kelvin-Varley divider and a null meter. I spent about a year confirming my voltage standard was stable, and used ovenized standard cells to do it. Naturally the reference I designed with was discontinued as soon as the design was complete. Anyway, I have both saturated and un-saturated Eppley cells, plus I collect technical books. There's a lot of information on standard cells that's been published, but it seemed like there was room for another write-up that pulled it all together. How well I succeeded I've no idea.

Tonight I'm going to take a shot at balancing my import mill/drill. My guess is the mechanics are pretty good, but the belts are the source of much vibration and finish problems. It really needs a pair of link belts, but the belts are wider than a standard narrow V-belt. No doubt those are even more expensive than standard. My initial plan is to chuck up a small motor and drive the spindle directly. The top pulley is huge, so if it shakes, that's probably where the problem lies. Then I'll move on to the motor and idler.

Best,
Conrad

Jiminee Christmas.....nice collection of test gear....

Do you have any interest in CNC machines???

dkmc said:

Jiminee Christmas.....nice collection of test gear....

Do you have any interest in CNC machines???

Click to expand...

Yeah, it's an addiction. I tell myself the collection keeps me employed, but the fact is some items only get used every decade or so. Most items were acquired over many years of going to hamfests, surplus dealers and only a few from eBay.

I have no lack of interest in CNC equipment, just little access and less time to think about building some type of diy something. My interests are more towards ultra-precision stuff- I seem to spend a lot of time honing, lapping and fitting things, though my error rate doing things by hand is high enough that I wish I had CNC. Right now I want to build an air bearing tone arm and turntable, but I've no idea when I'll get to it. It's laid out in CAD, but that's just not the same as cutting metal.

Tonight I took a first look at my mill/drill. I was wrong. It seems the place to start is the motor. Pulling off the pulley, it still transmits a lot of vibration to the support plate. I've heard a lot of horror stories about the import motors, but this one's been good to me for going on 20 years. It's an early Grizzly #30, or whatever they called the heavier one. Back when the first thing after delivery was complete disassembly and deburring of all the razor edges, and readjusting of everything. Or are they still that way?

Best,
Conrad

I looked at the spreadsheet, and only see text, no equations. Is there something I'm doing wrong?

Conrad, what did you use for accelerometers?

I see you have a little HP in your collection. I'm an old HP tech, now Agilent, test and measurement.

Forestgnome said:

I looked at the spreadsheet, and only see text, no equations. Is there something I'm doing wrong?

Click to expand...

Go to the second page via the tab on the bottom left corner.

Raymond

Yup, tabs!

I have a few surplus accelerometers, mostly PCB Piezotronics and a huge Wilcoxon seismic sensor. Any of them seem to do the job ok. IMHO, given the high cost of the piezoelectric stuff, the best solution today is to use the MEMS devices from Analog Devices. The quantity price of a common one is under five bucks. Spark Fun Electronics sells them on circuit boards for something like $30, but then you don't have to contend with mounting a tiny surface mount device. You can also modify and use a small loudspeaker as described in the spreadsheet.

Best,
Conrad

Conrad Hoffman said:

... Spark Fun Electronics sells them on circuit boards for something like $30, but then you don't have to contend with mounting a tiny surface mount device. You can also modify and use a small loudspeaker as described in the spreadsheet.

Best,
Conrad

Click to expand...

Thanks for the Spark Fun alert, their products and pricing makes it possible to try ideas "just for the fun of it". I also have a bunch of boxes of PCB sensors (mostly pressure transducers) which did last longer than the others but the cash outlay was high. Furthermore I think their sales department has really gone downhill in the last decade.

Raymond

RDL said:

Go to the second page via the tab on the bottom left corner.

Raymond

Click to expand...

Unfortunately I'm using Excel2007 and it's only showing one page. Something wrong with compatibility mode. Microsoft sucks!

Found it! Had to change to "full screen" view. Not pretty, but it works.

Forestgnome said:

... Microsoft sucks!

Click to expand...

It just reinforces the feeling. I just rebooted the computer because my DAQ program was wonky for no apparent reason. Restarting the program did not help but restarting Windows had everything sorted out. ??? Of course Microsoft does not want to trouble the user with useful messages. More time and money was spent on useless animated paper clips and dogs than getting the operating system to work bug free.

Raymond

FWIW, I also use OpenOffice on one of my machines. It has its own quirks, but overall it's pretty decent. My spreadsheets and Word documents go back and forth with little trouble except the formatting of Excel comments. I got tired of single line text in the balancing sheet, so I tried just inserting a Word doc for the text. It seems fine here, but let me know if it's odd on other versions of Excel.

Too busy to continue work on the mill/drill balancing, and I think I really need to throw together a pivoted platform to do the motor well.

I have to wonder how PCB Piezotronics and Kistler do with their high prices, when the MEMs stuff is so cheap and works so well for garden variety tasks. These subversive comments belongs in a different forum, but I have to wonder if ISO9000, Total Quality and maybe GD&T make low volume and specialty firms completely non-competitive. Every company I've dealt with that adopted those things got harder to do business with, with no perceptible change in product quality. They make sense for high volume operations, but there doesn't seem to be a satisfying business model for low volume scientific and specialty manufacturers. [/end rant for now... maybe]

Well.. Sir Conrad Hoffman you are one of the special ones.

You have contributed something very special to this site. And you have done this before you ask the membership here for any help. What you offer this site is right on point!

To me that is very special.

Many "Nubees" feel we experienced tradesmen are here just to "carry" novices into this trade. When in reality, we are here to help each other who make our livelyhood in machining.

I'm repelled by, "I just bought a vertical machining center and I don't know how to turn it on. I need help because I have this new job I have to deliver." Sheesh!

Just my rant...

Best regards to you,

Stanley Dornfeld

I cannot get the second page using Excel 2007 to read the original file. Anyone have any pointers?

Years ago I built a Quorn tool and cutter grinder. The spindle motor is 1/4 hp GE single phase motor bought as industrial surplus. I found out why it was surplused: it vibrated so badly that the remotely mounted starting switch would re-engage the starting winding. A friend made a balance stand for the rotor, a pick-up from a loudspeaker coil reading a moving magnet on the balance stand, some pulse shaping circuitry, and an old neon timing light. We two-plane balanced the rotor and the motor is still in service.

One of my next projects is to build a small Gisholt style balance stand and learn more. Vey much interested in what you guys are doing.

Carl

I'm still using Excel 2003, so that's probably the problem. Lemme see if I can save it at work with the newer version.

Metalcutter- you make me blush. The other day I put a hundred parts in a lapping machine, set the timer and went to a meeting. I missed on the time a bit because when I came back to check the progress, I discovered I had lapped all the parts to zero thickness. Yup, completely gone. So, the only special thing I've done lately is be a special idiot!