I think I understand the inherent difference betweeen a soft bearing and hard bearing balancer. Please forgive my ignorance and correct me if I am wrong, I have never seen any of this type of equipment before. Obviously a soft bearing balancer would have some allowable movement of the bearing point which would translate either movement or force to a transducer. Does a hard bearing balancer have any allowable movement of the bearing/v block carrier built into the balancer, or would the transducer just pick up the vibration of the assembly that is tranmitted into the bearings and base. How are the tranducers usually mounted on hard bearing balancers? Is the base of the transducer isolated from the vblock/bearing? I really need to see a couple of these balancers to better understand the primary differences between the two. Google images has no detailed images that would reveal differences. It would seem that a soft bearing balancer would be far more sensitive to find small imbalances, but with the detriment of not having a perminant calibration, correct?

Thanks in advance!
AP

Andy - I am in the balancing business in the Sugar Land area - if you need some details give me a call and I can provide some technical as well as practical explanations. 281.762.5703 or email bsg@grandecom.net.

Dear Andy,

You've just raise a question that many people face when in the process of choosing the right equipment for their needs.

1- If your rotors are not very heavy but require more than just average balancing, then your choice should be a soft bearing m/c.

Justification : As you so well stated in your post, a soft bearing m/c actualy measures the movement of the rotor in question. They are usualy belt driven with a tensioner fitted at the bottom of the mounting base. Being belt driven, one can change pulleys to attain balancing speeds close to operating speeds.

Some newer models now have at each pedestal a small unbalanced motor and/or some sort of exciting unit that vibrate in order to make the set-up for plane separation very easy; therefore, when balancing a rotor in two planes, during your initial set-up, you get one pedestal vibrating and with appropriate dialing of the plane separation controls of the m/c, you null out the effect of this vibration on the other pedestal. You repeat the same thing in reverse for the other pedestal.
This is important because you always want to read the 'thru' unbalance of the one end of the rotor without the influence of the unbalance at the other end.

2- If you're handling large and heavy rotors, then a hard bearing m/c is your choice. But, it has limitations.

Justification : A hard bearing m/c works as you stated, but it has some drawbacks. They do not measure movement but force. They are driven thru a universal joint and have about 3 speed selection. They are usualy destined for large heavy rotors that do not normaly run at high operating speeds. Since they read centrifugal force and we know that the CF goes up by the square of the speed, then the hard bearing m/c can only read the force that is produced at the balancing speed.

The set-up is easier tho. You dial in measurements of rotor size, distance between pick-ups, etc.

Sorry for the long response,

Hope to have been of some help.

MarkoLeo