GD&T for 2 keyways on an impeller for a pump.

[ittuser01]

I have 2 keyways that are the same for an impeller that will mate up with a shaft. The questio is how to relate the two keyways to each other using GD&T. I've attached a jpg. for scenerio. i was thinkng of making the bore datum b then a surface datum A like shown in the attachment. then one of the sides of the keyway a datum. I would apply perpendicularity to the bore to datum A, position of the keyway width to A and B but what about the second keyway in relation to the first one???

 

[powerhound]

Control the perpendicularity of the bore diameter to the face. Make the bore diameter a datum and use position to locate the keyway to it. Make the shaft diameter a datum and use position to locate the keyseat to it.

You need to use a virtual condition calculation to make sure the slots will always allow a key to properly interface with them. If it's a 1/4" key then each slot should be something like .250 +.005/-.000. Then use a callout saying "position within 0 @ MMC WRT datum X." There are other ways to do this but this one is pretty straightforward. I'm assuming you are familiar with the Zero at MMC concept.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[lifttrucks]

If the two keyseats are in the bore, I would recommend making the bore the primary datum feature.

I don't think it is necessary to make one of the keyseats a secondary or tertiary datum feature to control their relationship to eachother. Since the keyseats are a pattern of features, you can use a composite positional tolerance to tighten their relationship to each other. Assuming the keys do not have an interference fit with the keyseats, you can specify the positional tolerance at MMC.

 

[greenimi]

ittuser01,

If you use position of both keyway to the same datum reference frame (DRF) the simultaneous requirement rule, will take care of the "the second keyway in relation to the first one"
Therefore, you will have a position of the first keyway to a DRF and another position callout of the second keyway to the same DRF, in the same datum order of precedence and with the same modifiers AND THEN the simultaneous requirement will establish the relationship between the first and second keyway.

 

[greenimi]

Fig. 4-40 and Fig.4-41 from Y14.5-2009 standard might help on how to relate the two keyways to each other via simultaneous requirement.
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