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Thread: Electrical runout?
08-27-2009, 04:13 AM #1
I'm working on a 97" long 6" dia. shaft made out of 4150 steel for a big electric fan, one of the specs is for the bearing areas to have no more than .00025 Mechanical and Electrical runout, what is electrical runout and how is it measured, some kind of special instrument we don't have I imagine.
08-27-2009, 06:13 AM #2
08-27-2009, 08:38 PM #3
Could they mean axial displacement between fan shaft and motor shaft? Works out to slightly less than one hundreths of a millimeter which I find an exaggerated demand. Is there a coupling of some sort to allow displacement or is it just a very stiff connection? Just my .02 Euros.
When you find out, please post. I'm intrigued!
08-27-2009, 08:57 PM #4
I think it has something to do with the magnetic properties of the shaft.
08-27-2009, 09:32 PM #5
I can think of several possible meanings, but none of them apply to the shaft alone. They would only apply to the shaft plus the rotor.
I am supposing they refer to mechanical and electrical/magnetic balance, not just specifically runout.
08-27-2009, 10:27 PM #6
I suppose it is possible that they don't know what they are talking about. Or don't know how to properly specify what they want. Or is that the same thing??
Last edited by becksmachine; 08-27-2009 at 10:34 PM. Reason: Forgot rest of post!
08-27-2009, 10:41 PM #7
08-28-2009, 06:24 AM #8
08-28-2009, 07:47 AM #9
The first question should be, what are the units? The .00025 could be inches, mm, feet, angstroms, farads, mmg or whatever.
08-28-2009, 07:58 AM #10
I deal with this every day - it sounds like you are looking at an API requirement as that tolerance is common in many of their rotating equipment specs. It's hard to meet. Or rather, it's hard to meet if you have to guarantee it. Sometimes you'll hit it, sometimes you won't.
Generally the tolerance is applied to the area of the shaft where the Bently Nevada (or other type) proximity probes will read - any imperfections in this area will be picked up as vibration.
Mechanical runout is just what it sounds like - non-concentricity of the shaft. Electrical runout is caused by irregularities in the shaft steel that will be 'seen' as non-concentricity.
08-28-2009, 08:18 AM #11
08-28-2009, 10:09 AM #12
Who in the world dreams up these outlandist terms? Other than to drive you nuts figuring it out, does it really mean anything different than the normal terms of trueness or tolerance would mean?
The term "Electrical Runout" for machining sounds ridiculous to me and after gregsy's explanation it still sounds ridiculous.
08-28-2009, 10:12 AM #13
To eliminate guessing,GOOGLE IT.
08-28-2009, 11:09 AM #14
One possibility is that they're referring to use of an electrical (electronic) profiling system.
A device that measures capacitance can perform dimensional measurements with extremely high resolution and accuracy. The probe is placed very close to the work being measured, then the work is rotated on axis.
Any change in the distance between the probe and the work is easily measured.
08-28-2009, 03:15 PM #15
Could them be a translation problem, as eliptical rather than electrical?
08-28-2009, 04:04 PM #16
I'm interpreting it that the part may be subject to an electrical measurement for run-out/vibration. If the steel is non-uniform ( electrically) then the gauge will not readout correctly, and will not indicate run-out correctly.
If the steel had various inconsistencies floating in it, it might be mechanically true, but will not readout correctly when measured electrically.
But then again, I could be wrong.
08-28-2009, 04:59 PM #17
The capacitance between two conductive plates is solely a function of the overlapping area divided by the separation. No other factors are involved.
In particular, the composition and homogeneity of the materials do not enter into the calculation, provided of course that they can conduct electricity.
08-28-2009, 05:12 PM #18
Even for a magnetic probe?
08-28-2009, 05:13 PM #19
Yep, google it here www.freepatentsonline.com/3986380.html
After reading the whole looooong page I still don't know what purpose or effect electrical runout does or has but I know how it's found and corrected.
I guess instead of the electric pencil you could use a chisel and hammer
After reading the article it sounds like something Rube Goldberg would come up with.
08-28-2009, 05:24 PM #20bearing areas to have no more than .00025 Mechanical and Electrical runout