Run out calculation

[Radius1]

I am calculating the axial run out of a disk that spins on a shaft with bearings.

See this example (not mine) of checking the axial run out.

Also see the definition of axial and radial run out.

I am given the radial run out values of the bearing cup and cone. why would these radial run outs affect the axial run out of the disk? I have a few folks arguing that these would.

My thought is that if perhaps, one bearing out of two had radial run out, this might cause the disk to wobble in the direction of the dial indicator. Otherwise, the radial run out of the bearings would not affect axial runout.

 

[3DDave]

If there are two bearings then yes, radial runout of the bearings can be seen as axial runout in the face. If the shaft overhangs the bearings that can also amplify radial runout at the overhanging end of the shaft.

 

[Radius1]

Hi 3DDave, can you please help me visualize it?

 

[3DDave]

I thought you had it with "cause the disk to wobble"

Take a pen or pencil. Hold it upright with the point at a fixed spot and move the free end in a circle. It will make a changing angle. Anything attached to it will also change angle.

 

[Radius1]

Thank you.

 

[mfgenggear]

Radius
Ever heard of stack up.
The datums have to be held precise. The run out of the datums to each other and datum faces will affect all other surfaces,.
For example if have a shaft with two bearing diameters, one on each end. I have a center diameter. That has to run out to both datum within
.001 inch run out. The two datum must run out .0005 inch or better to maintain that center
Diameter runout. The tolerance is semantics.
But this explanation is that to maintain other run outs it is critical to hold the datum as perfect as possible.
In the case of your disk rotor, faces have to be square to the bore. Machining runout held to obtain the requirements

 

[Radius1]

mfgenggear,

A stack up is exactly what I am trying to compute to confirm what the run out of the disk face.

I will see if I can post an example that I am working though.

 

[mfgenggear]

Yep it's like squaring a block. Clamp on two surf the initial locating surface can be ruff.
Machine two or three surfaces to maintain squareness, and runout. Now flip the block locate on the machine surfacec. Mill the other surfaces.
It's machining practice to machine surfaces at the same time when possible, it will concentric on round parts, square and parallel on rectangular or square parts. Holding datum precise to each other is the key.