controlling bored-out boss

[MattBD]

I have a part that whose outside shape is two stacked cylinders of different diameters.

(forgive the ASCII art)

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There is a bore in the larger cylinder. I want to control these three features so all are concentric. I realize that I want to use position or runout here. How do I determine which to use? What does one "buy" me vs. the other? The small cylinder bottom flat is datum A and its diameter is datum B.

Thanks,
Matt

 

[ewh]

For ease of inspection, I would use runout on the outer diameter and position on the bore. You could use position on both, but runout would give you more control of the circularity. It may be difficult to inspect runout on the bore, which is why I suggest position.
I am sure others will have more detailed recommendations.

 

[dingy2]

It would depend upon the usage of the product. If the part assembles in a mating hole, then I would use positional tolerances at MMC related to datums A & B at MMC. That simulates assembly and also allows one to develop a checking fixture.

If the product does not assemble in a mating hole, then I would agree with ewh and go circular runout. That will control the roundness and concentricity of the larger diameter to the smaller one but it does take a bit of skill to perform the check.

I agree that the bore should be positional at MMC to datum A and datum B at MMC. One could also use circular runout again but it is difficult to check.

Hope this helps.

Dave D.

http://www.qmsi.ca

 

[ctopher]

I agree.
It depends on how the part mates to other parts. How do you want to position/control it.

Chris
SolidWorks 07 2.2/PDMWorks 07
AutoCAD 06
ctopher's home (updated 03-13-07)