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04-17-2012, 09:59 AM #1
Measuring shaft run-out using balancing ways
We have a large rotating assembly that has a relatively high clearance plain bearing on either end. The plain bearings have a running clearance of about .030" and are 18ft apart. The bearing surface is about 8" diameter and 9" deep.
I am measuring run-out on the shaft ends by placing the entire assembly on pillow block balancing ways. They are placed as in-board on the bearing surface as possible. Then I simply place a dial indicator on the outboard end of the bearing surface and rotate the assembly.
Does this sound like a reasonable way to measure run-out in this situation?
04-17-2012, 11:33 AM #2
Use V-blocks with NYLON liners or pads, and measure it in that, it is the best way to measure run-out as there is no influence from the measuring surface, and the bearings should eb the datum to with the parts are machined.
I will post some more stuff later, you need to be sure to measure perpendicular to the vee-block surface.
04-17-2012, 02:15 PM #3
I'm more interested in the axial alignment of the shaft ends than the diameter. Measuring directly at the balancing way location I get about .0005"
Does this make sense, or is it a bad way to go about this? I see what you mean with the soft surface v-block, however it seems like the balancing ways provide a similar setup.
04-17-2012, 09:04 PM #4
04-18-2012, 11:24 AM #5
springs work on the mas exerted on them at any point, if they have "Give" once you have placed the item on them, they have already "Gave" they are not going to give more as you turn the component.
The nylon is used in the most precise of rotating equipment, (API industrial standard), we measure below tenths on it all day, it is far more acurate than any other method available.
The balancing ways are roller bearings, correct?
Roller bearings have run-out, a dead material has no run-out, it is a reference surface.
One note, this is assuming you want to measure surfaces with roundness in the 0.0005" area or less, this method is not necessary for measuring a very rough or non circular surface. the bearing area of the nylon needs to be somewhat constant in order to function correctly, as stated by you it is more giving, (Much lower elastic modulus than steel about 100 times) and will give some due to differences in surface area contacting the nylon. but if the area round to 0.0005" or less we are talking 0.0000001" difference or close to that in the measurement of run-out. You can use steel to steel, but you must worry about galling. 0.0000001" is much lower than the run-out in nearly any roller bearing.
I came up with the numbers using hertzian contact stress equations.
04-18-2012, 11:30 AM #6
04-18-2012, 02:47 PM #7
I'm expecting run-out of up to 0.010" and would not need to measure with any precision beyond 0.001"
Balancing ways do have roller bearings, the runout in the ways is measured quite easily.
Really I'm looking for some verification that my inspection set up is one that will give a usable measurement when questioning the amount of run-out inside of the plain bearing.
04-18-2012, 11:53 PM #8
if all you are doing is measuring to 0.001" you will be fine on balancing ways.
04-19-2012, 01:22 PM #9
This thread has been very enlightening. Thank you!
04-19-2012, 01:43 PM #10
Thank you for the information. The nylon does make good sense.
I prefer the balancing ways in this scenario because after the assembly is complete and we take our measurements, I need to static balance it!
09-26-2012, 08:42 AM #11
We're working with very large shafts that are difficult to turn due to their weight. Any information on v-block liners/pads is appreciated.