maybe OT, how were large old motor bearings aligned?

I figured someone here may have an answer to a question that keeps coming up in my mind. Every time I see pictures of large old motors or generators, the sort from the 20’s, I wonder how they were installed. Specifically the armatures had separate mounts from the shaft bearings with no common base. Just separate concrete stems from what I’d presume to be a common footing. How were the footings layed our to be aligned and then subsequently how was the armature installed and the mounts/ bearings shimmed for alignment and concentricity of the armature and rotor?

Early in my career I worked on a slab of concrete for a turbine generator. There was a piano wire stretched down the center line about 7 feet above the finish. There was a 30 or so gallon metal bucket full of sand suspended 2 or 3 feet off the ground providing tension for the wire.

Plumb bobs were hung and all the measurements were taken from there.

Dunno if any others were done like this....

Large motors frequently had "kingsbury tilting pad bearings" which are akin to kingsbury thrust bearings except the force is not axial but radial - and the bearings are not sections of a plane but sections of a cylinder. Usually at least four pads but possibly more.

Kingsbury bearings are inherently self-aligning once set up via the tight wire method.

Same hydrodynamic wedge of lubricant forms from shaft rotation.

Joe in NH

What has already been said. And "Oh, BTW".. as it is ultimately the bearings that determine where the shaft's "real world" line of rotation will be?

Once in-place, any error can be measured directly, eg; centering, & clearance, rotor to stator. The bit with wires - or optics, or.. whatever.. just gets one to the best practical starting point. Done right, it is final. Done not-quite-right, THEN one shims.

Tedious, yes."Magical", or mysterious? Not even close.

I have read that line shaft bearings in factories were aligned using piano wire also. A wire was put in place first and all measurements were referenced to the wire. Catenary tables were used to predict the amount of sag in a long wire under a known amount of tension. The wire was the last tool removed when the building was completed.

Bob
WB8NQW

blcksmth said:

I have read that line shaft bearings in factories were aligned using piano wire also. A wire was put in place first and all measurements were referenced to the wire. Catenary tables were used to predict the amount of sag in a long wire under a known amount of tension. The wire was the last tool removed when the building was completed.

Bob
WB8NQW

Click to expand...

Transits, theodolites, optical levels... all used, too, "back then". More precise than most folk are aware they were, most especially when used under-cover where winds and thermals (yes, both affect line-of-sight in "air") were less intrusive. Precision differential autocollimators even more so. Lasers, now silly-cheap, used nowadays as well.

thermite said:

What has already been said. And "Oh, BTW".. as it is ultimately the bearings that determine where the shaft's "real world" line of rotation will be?

Once in-place, any error can be measured directly, eg; centering, & clearance, rotor to stator. The bit with wires - or optics, or.. whatever.. just gets one to the best practical starting point. Done right, it is final. Done not-quite-right, THEN one shims.

Tedious, yes."Magical", or mysterious? Not even close.

Click to expand...

YES

BTDT although not with a REALLY big machine.... The adjusting comes after you think you have it right. Because the rotor may not be just how you think it is, and there may be shaft sag, etc. Roll it over "by hand" (that may involve barring it, or the equivalent) and check clearances before even thinking about any power.

JST said:

YES

BTDT although not with a REALLY big machine.... The adjusting comes after you think you have it right. Because the rotor may not be just how you think it is, and there may be shaft sag, etc. Roll it over "by hand" (that may involve barring it, or the equivalent) and check clearances before even thinking about any power.

Click to expand...

Year or so before he retired, Dad proudly dragged me out, just before dawn to show that he had had the contractor, Opekiska Lock and Dam, craft the towers and guide channels for the pond-control "Tainter gates" to a precision that in still air, the rollers never touched the guide rails closure to full lift-height, AND.. the downstream side was DRY until dawn sunlight began to bow the gates and allow a thin sheen of water to creep past the lips.

He was something of a legend, USACE, for that s**t, but the contractors loved it anyway, because he was ALSO always showing them how to beat time and reduce costs to DELIVER better than spec, ahead of time, and under budget.

And an interesting aside: Central station turbines may have as many as 9 bearings, and potentially a couple of more for the exciter, oil pumps.

The bearings are NOT in a straight line, but are rather designed into a "catenary curve" to match the accumulated sag of each of the perhaps four or five major turbine shafts. The low point of the sag is typically one of the center elements of the turbine, with each section added on each side beginning where the center left off and ending at its own curve - which changes depending on the normal sag for that element.

"Rolling" a turbine to operating speed is complicated because of the catenary where each element has its own rotating vibratory response which when matching its natural resonance is known as the "critical speed." Critical speeds are typically above 1000 rpm but less than the 3600 rpm normal turbine speed. Generally one wants to go through the critical speeds (there may be more than one) "quickly" lest the vibration feed on itself in resonance to failure.

Joe in NH

Ahh, thanks, makes complete sense after the fact. Also, for orhers that are curious found this thread here that seems to contain an in depth explanation of the exact process.

https://www.practicalmachinist.com/...-t-power-plant-machinery-circa-1954-a-350842/

One thing not mentioned is how do they rig the armature thru the stator ?

Don't bump the windings.....

thermite said:

Transits, theodolites, optical levels... all used, too, "back then". More precise than most folk are aware they were, most especially when used under-cover where winds and thermals (yes, both affect line-of-sight in "air") were less intrusive. Precision differential autocollimators even more so. Lasers, now silly-cheap, used nowadays as well.

Click to expand...

.
optics been used a long time. sure before optical micrometers were common many just estimated between mm lines to nearest 0.1mm or used a 1/100" or 1/50" ruler and could see .005" if not too far away.
.
normally at 100 feet 4 arc seconds is .024" thats the limits of when ruler lines appears to blur together. if using 0.1" ruler you can guess to .010" at 100 feet but if air temp unstable you get a shimmering air effect.
.
once had sole plates rough leveled to 1/16" over 100 feet and turned a steam heater off. laser then said sole plate were over 0.3" off. need stable temperature for relaible readings

digger doug said:

One thing not mentioned is how do they rig the armature thru the stator ?

Don't bump the windings.....

Click to expand...

Very carefully.
1. Rig the rotor level to a 98 level hanging from the hook on Kevlar Twin Path endless slings.
2. In the stator a metal trough shaped to fit is laid on fish paper and tied at the ends with rope. The trough is waxed heavily.
3 affixed to the rotor are a journal shoe,mounted to the turbine end journal and a field shoe strapped to the turbine end of the rotor. These are Maple and heavily waxed.
4. The crane lifts the rotor and starts it into the stator as far as possible with journal shoe over the trough, then lowered so that it rests on the trough
5. on the exciter end of the rotor there a temporary stand called the "tombstone" that will allow the crane to either stop and get a fresh "bite" near the exciter end or to remove the rigging entirely. On smaller rotors you can slide it in all most all the way by getting that "bite" closer to the exciter end.
6. On large rotors , like nukes which are 200 ton plus the crane will support the exciter end while a winch pulls it in.
7. when the journal shoe reaches the end of the trough the crane lowers the rotor so that the field shoe takes the load and allows the rotor to go all the way in.
8. when the rotor is all the way in and the turbine end resting in its bearing the exciter end is suspended with a cradle and the trough and fish paper and winch rigging are removed.
A really ass kicking crew can do a 200 + ton rotor in about 8-9 hours.