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How to place correct GD & T on eccentric shaft?

How to place correct GD & T on eccentric shaft?

How to place correct GD & T on eccentric shaft?

(OP)
Attached is an image of my drawing of an eccentric shaft. I don't think what I have is correct. There are bearings on each of the datums that I have called out (except the keyway of course "G"). The keyway is strictly driving the shaft and its location is probably not critical, but I used it as a datum to orient the shaft diameters in line with it (see the end view, as all the shafts are on the same centerline). I don't think I can call out the centerlines as datums either. I also don't think my runout conditions are called out correctly either. Any help would be appreciated!

RE: How to place correct GD & T on eccentric shaft?

No, you cannot call centerlines as datums, but the way you did it is good enough. Runout also can be specified the way you did it.
I am not sure what your diameter .438 is.
If it’s distance between the axes, then remove diameter symbol, make dimension Basic, and specify Position on your shaft diameters.
Then we will see.

RE: How to place correct GD & T on eccentric shaft?

(OP)
Thanks checker! The .438 diameter was an oops on my part and is a distance between axis. (likewise, the 2.496 was incorrect) The question came up via my checker here about the runout and the way I called it out. He seemed to think it should be detailed this way (see attachment):
He did not think you could have a runout tolerance called out on a datum and I could not find any examples in my gd&t books either. I wonder if I removed the runout condition and did as you said add a position callout to each of the diameters...maybe that would be better? Another thing that is confusing is -what if there were no key seat? How would I define the orientation of each of the diametrical lobes? I would still want them to be in line with each other.

RE: How to place correct GD & T on eccentric shaft?

Like I said, this kind of Runout call-out is quite common. (Although it may not be always clear, how to check it in real life) See picture.

If you pick two lobes as your datum and apply Position to other lobes wrt first two, they will be oriented to each other by what's known as Simultaneous requirement. Check your GD&T books.

RE: How to place correct GD & T on eccentric shaft?

I would pick your 2 main bearing diameters and position the rest with basics for the eccentricity, I would not use runout, and all the extra datums unless there is alot more to tell that you are not showing?
Frank

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