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### Author Topic: Need Guru input on an idea: Using Mach as dynamic balancer  (Read 15688 times)

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#### NosmoKing

• 238
##### Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #20 on: May 20, 2010, 04:21:40 PM »
You make a valid point, but limited to something that should be and eventually will be symmetrical. I was thinking in terms of a workpiece (or assembly) of some odd shape that will have a monstrous imbalance before during and after the cut. Cutting such a part in extreme slow motion is one solution, but often that will result in an intolerably low SFM or intolerably high production time.

You would agree, methinks, that the closer you can bring the part into balance, even a very rough balance for example by bolting a bob weight to a rotating fixture or even just a face plate, the faster you can spin it for the needed operation.

I have followed this with interest and right off the bat let me say I know nothing about the physics of off balance rotating objects.
BUT I did find this explanation on the web.
What is an unbalanced wheel?

An unbalanced wheel is any device capable of repeated rotation in which
any given point along the circumference is either

A. prone to stop in a given position along that circumference as opposed to
any other, regardless of the amount of force inputed into rotating the
wheel, or
B. prone to rotate indefinitely according to the principle of having a
constant and recoverable force which acts on one half of the wheel more
than the other.
OK, presuming I understand this to mean that in an unbalanced rotation condition, the rate of rotation  varies at any point on the circumference?
What I am leading up to is if you have a spindle that has an encoder, and you capture the anticipated position on several points on the circumference, due to imbalance, the following error on the spindle will vary, and the captured positions will vary.
Although Mach per-se is a bit of overkill to achieve this, if you already had, say Mach with a Galil card, Galil has a feature called high speed capture that possibly could be used with a high speed capture input, lets say you had 4 sensors on the spindle input to the high speed capture, they could be referenced off of the marker pulse so you could identify the quadrant that required the 'Bob' weight, which if the system works, could be done initially at low rpm?
Actually I just though of a method that may not need sensors, this is the use TE tell error at given positions at degrees of rotation.
Of course I could be right out to lunch with this theory, if so please ignore it.
Nosmo.
« Last Edit: May 20, 2010, 04:30:55 PM by NosmoKing »

#### RICH

• 7,412
##### Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #21 on: May 20, 2010, 09:48:25 PM »
Balancing a rotating object is done to reduce the loading / forces that the machine will see. Need to really  call it a system. In that light the bearings will have greater life,
improved machining, etc. You can run in an unbalanced condition as long as the forces can be tolerated by the system configuration or the task at hand.

You ever wonder why they put that adjustable collar on an Albrecth chuck? What do you do with it?
Why level a lathe? Don't they use them on a ship at sea?
Is the mill table leveled such that when a horizontal 4 th axis is used as a  component of the system, if balanced, takes advantage of the additional efforts done to it?
Why balance the rotor of a motor or the impeller along with it's shaft for a pump?
How come some machines are massive and some are not but they have the same stated turning capacity?
What happens when you add all the unbalanced crap onto a balanced HP car engine? What do you get for all that additional money and effort?
Why spend the money for a hand spindle foriegn made and not spend an extra bunch of money for a name brand ( could be as much as 5X in cost)?

Just some things for ya to think about.

Lets give some vibration and resonance examples form true experiences:

- 10 foot diameter x 60 foot high vessel filled with liquid lifting it's base ring and shearing the anchor bolts.
- Watching a 8" schedule 40 stub end on a 20" pipe sheer off
- a heat exhanger still attached to it's  concrete base shear the pad and bouncel up and down when resonance occured ( 4 ft dia x 10 foot long heat exchanger )
- my favorite and relative to what Steve mentioned about a unbalance during turning:
So the 1200# lathe is leveled and anchored to a 4" thick table which is bolted to a steel frame which is anchored 5 places to a concrete block wall.
An odd shaped piece  is mounted to a face plate and the tail center used to add some hold / rigidiy. I will guess about 5 lbs for the piece and turning off center some 2".
Slowly machine off some of the casting, crank up the speed and refine the cuts, ok, hech turn up the speed and lets get her turned ........
Well before i could  reduce the speed, the inbalance created vibrations which happen to hit a resonant frequency of the sysytem, and in about 3 seconds,
the lathe lifted the base and pulled the anchoring out of the wall. Not something you want to be standing by or experience.

Even if the piece was counter balanced before starting, the eccentric loading while spinning, the balance will vary as mass and rpm change
thus the affect  relative to vibration or resonance is not constant due to a changing natural frequency of the system.

RICH

« Last Edit: May 20, 2010, 09:50:53 PM by RICH »

#### simpson36

• 1,371
##### Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #22 on: May 21, 2010, 11:48:43 AM »
While the topic of balancing is interesting to discuss, the thread was intended to be specific to exploring the possibility of using Mach facilities to perform some rudimentary balancing, for the benefit of all MACH users.

I have purchased an accelerometer, programmable controller and strobe that can do the job autonomously. That is how I will proceed from here.

Thanks for the contributions.

#### 1stcuts

• 5
##### Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #23 on: May 21, 2010, 04:07:44 PM »
You might look into the relatively inexpensive sensors used on the servo driven
washing machines. Whirlpool cabrio in particular. This is a top load model with
a glass door. During the spin cycle if an out of balance condition is sensed ,
the unit stops and repositions the load by turning the drum in one direction
while turning the agitator in the other. Then a test run up, and if green
lighted, continues up to 2000 rpm. Pretty impressive for a 100lbs of wet
cloth.

Slieghtly out of balance,

Bill

#### simpson36

• 1,371
##### Re: Need Guru input on an idea: Using Mach as dynamic balancer
« Reply #24 on: May 24, 2010, 12:37:28 PM »