With rotor kits usually costing from $2000 to $4500, here is an idea that you might want to look into: a common, dual-wheel variable speed bench grinder. The link below shows one example. I think I bought a different model (without the 'tool-less feature) for about $80. I will probably just make a couple of 'balance wheels' from baltic birch plywood (don't have access to a lathe).

I tried it right out of the box and it had enough vibration (no suprise) to generate a decent vibration signal. I set it on a piece of foam and the 1st critical was within the speed range (2200 - 3300 for the model I bought) of the unit.

This would be a very cheap way to investigate the phase shift behavior we've been discussing. It produces a nice, slow coastdown. By adding a couple of bolts with wingnuts you could vary the mounting stiffness (with the pad underneath) to move the resonance around.

The 'pad' I used comes from Wal-Mart... it's a flat closed-cell foam pad used under sleeping bags. I also use it for padding in my instrument cases, tool bags, etc.

http://www.lowes.com/lowes/lkn?action=productDetail&pro...757-GR450&lpage=none

This message has been edited. Last edited by: rustythevibeguy,

Interesting approach given a recent statement you made.

quote:

...I didn't mean to imply that someone who uses less expensive equipment is a "discount consultant".... if it works, it works... no matter what it cost. But in my opinion, most clients are not going to be impressed by how "little" a consultant pays for his equipment. Sure in the final analysis it's the value you add and the results you achieve that determine if you stick around. But first impressions do count, and in a political plant environment 'perception' is often as important as reality.

I guess this rotor kit would be for self enlightenment only rather than training. They plywood wheels might not favorably impress a client, nor the whole setup.

One must be careful with rotating equipment.

I really like Rusty's "style" here. Fundamentals are fundamentals, and they don't change with the specific configuration. He could learn more from measuring and understanding the behaviour of the "realities" of his rig, than from a more "precision" set-up with more perfect control of the variables.

Many years ago I bought a Sears variable speed bench grinder and had a machinist make two aluminum disks that are 3/4" thick and 6" diameter. A series of drilled and tapped holes (axial direction) around the perimeter allow for various length set screws as balance weights. I also had a groove machined inside the holes to allow for clay as balance weight. I have used this for training seminars to demonstrate:
1) Measument directions (H,V,A)
2) Waveform, spectrum and phase
3) Natural frequencies (by variable speed and impact test)
4) Electrical vibration
5) Single plane balance
6) Dual plane balance

My advice is to forget about the plywood disks.

Walt

Rusty,

I think this rotor kit may have following limitations in simulating real life conditions.

1. overhung rotor only.
2. due to relatively heavy weight of the shaft (motor rotor core ) the center of gravity of the shaft will be somewhere between the bearings.
3. both bearings have same stiffness.

David

Rusty,

I used my bench grinder to check balancing procedures. A pulley with spokes replaces the grinding wheels. A garden hose section slit and wrapped inside of the pulley wheel makes a quickly added and changed eccectric mass. Secure the hose with strapping tape for added safety. However I would never show this to a client.

A model is a replica of the real thing. Remember that the next time your wife calls you a model husband.

Move to a state where they have machine shops: the flintstones re-visited.

Forget the client - I wouldn't want my child to see it nor the EMS folks when they come to get the imbedded parts from your chest. Come on, isn't this getting a little far fetched?

The old Don Bently model isn't that bad and can be memiced at home with not too much expense if you don't want to buy it. And it has an oil whirl kit and various setups that can be useful if you're wanting to train yourself. But I don't think you're going to get much training from a 'machined' plywood disc? What am I missing? Or, was this intended to mess with people's mind?

I'm in keeping with Walt here - a simple setup for a task with safety in mind. If you can't afford some simple machined discs, how will you afford the motor.

As Bill mentioned, you may get enlightened but at what cost? For everything else there's Mastercard (())(R).

Good grief, Sam... get your nose out of the air. I suspect that a lot of folks on this board don't have unlimited funds and do a lot of their "studying" at home, on their own time. I was just trying to help them out with this idea. As I said, I bought this rig to grind chisels and plane irons, but it will work fine (and safely) as a rotor kit. Sure machined aluminum disks would be ideal, but what do you thing that would cost? Baltic birch plywood, with the edges roundged over and then polyurethaned would be very safe and look quite nice actually. And I wouldn't be afraid for clients to see it. I can afford to buy or build anything I want to but I don't spend money on things that don't make me money.

Rusty,

The variable speed grinder that I have in my "R and D" department (my tool shed) has considerable drift in the speed control.

Maybe you, being a Vibration Analysis Mogul and everything, can afford to go out and spend 75 bucks on a brand new bench grinder, but us poor folks have to buy ours at yard sales.

I've got a 4' diameter axial fan in my attic that I plan to pull out in the spring and bolt down to the concrete behind my office. After taking all the proper precautions, I plan to use it as a balance trainer. Total budget-under $50. I'm not planning to show it off to my clients, but it will serve its purpose well.

Danny

Since when is grief good? Beside I like sniffing.

You deserve some ribbing on this one and many are willing to help. I think it was more "fun" than unkind; but anything to help.

But the plywood, stain, tung oil and replying to this harrassment - the aluminum disc may be cheaper than you think <;-)= Walt can afford it! Probably knows the cost and guess 4 hrs labor (really, not that much). And yes the unit I built at home some 25 yrs ago was from steel w/16 balance holes 1/4-20. I typically make balancing rings in that fashion for large verticals to attach to the motor.

I have to side with Rusty on this one. I bought an old lathe a couple years back for $300 bucks. It has a motor with a V belt which dives a spindle with a flat belt, which drives the main rotor with the gears. I can play with the speed, balance, alignment, phase, ect. and it even works well to make plywood disks.
Danny, you need to come see some of the good junk (treasures) I have come across through the years. I may have some FREE stuff you could use. (motors, pulleys, gears, widgits, ect.) I will even whip you out a couple plywood disks if you need.
Pete

Sam, I've been fretting all afternoon (out collecting data) about the 'tone' of my response.... glad to see you took it the way I intended it. I think it's good that we can have a little fun with each other. I am a bit of a paradox at times.... cheap about some things, extravagant about other things... aren't we all a little like that though?...

I bought a nice rotor kit a while back (on Ebay of course) but the motor runs slow... I guess I'll have to buy a new motor for it so I can have a "proper" unit to show to others.

Well, fellas, thanks for this discussion, my department has just started discussing setting up a rotor kit for post failure analysis purposes.
Of course we were thinking buying a proper "rotor kit" as the main idea, but we could probably save a pile of money, and have a little fun and training constructing our own. We certainly have plenty of "treasures" in the "discontinued equipment" warehouses.

Martin,

I used to use the Bently kit and althoug it is good. I like a real world coupling and a few things beefier so to speak. If you have a bunch of stuff to build a skid unit, driven machine change to sleeve from AF brgs and extra money to blow, you can build something that is not available off the shelf for general purpose training and demonstrations.

Rusty; I'm not that asleep yet - you want people in your boat so they can help row. getting all the mileage out of this I can Have a fabulous weekend Plywood won't rust, Rusty. He-he! Just like Toyota. Another fun Friday!

The safety issue is an interesting consideration. In a past life, we had bought the Bentley kit with all the bells and whistles. My coworkers ripped the box open, threw the directions aside (of course), added all the accessories, cranked the speed to max....and watched the shaft turn into a pretzel! This took less than 10 minutes from the time the package was delivered!

So whether you use a commerial rotor kit or a homemade version, use some common sense and think about safety!

Jon
Spintelligent Labs

Thanks for the safety report from Spintelligent labs.. I'll make a note of it.

What HP do you suggest for a reasonable mock up?

I am particularly interested in belt effects, multiple belts, load effects, and other variables.
I had the opportunity a while back to build vibration display a for demo. It consisted of a 1/4 hp motor variable speed, with a taper lock on an output shaft, connected to a journal bearing which could be moved on an adjustment table Horizontally to simulate alignment effects. I learned things from that simple set-up.

There is a company in Virginia (?) that seems to make rotor kits as their main businees - interesting kits.

The new Bently Nevada (correct spelling, not Bentley) rotor kit has a flexible beam type coupling - commercial 'real' coupling. I built a setup once for torsional vibration and used a 'shim pack' coupling (Rexnord, I think, good for 100,000+ rpm, off the shelf); this used Bently Nevada components otherwise - almost I had a torsional force generator with help of an electrical engineer (Don as I recall was the one who got this right - the other electricals had some issues.).

I was involved slightly to build a 'monster' demo rig one time with a surplus motor (Babcock and Wilcox had bought up spare parts from a not to be built nuclear plant). I had about a 25 hp motor, 1" shaft, very rigid. It was used to demonstrate a diagnostic system. These were spare parts that the company got in a purchase but had no intention on using. For a mass we used a pump impellor, drilled and tapped it for balance weights.

The correct spelling is "GE Energy Bently Nevada"

Bently Nevada is a brand of GE. It is also an LLC, still. That branch of GE Energy is OC (or was on Thursday) in which the Bently Nevada brand falls. I inquired as to the names this past week at an event where we had some Bently folks (and other vendors) present.

Since they still sell to what otherwise would be competition in other fields sometimes the Bently Nevada brand may sound kinder.