Datum target diameters 1

[destes]

I have a plastic cover that has a couple of different surfaces that I 'm using for Datum A with three target areas. The datum targets are around a ∅10mm hole that is used to mount the cover. I've specified a ∅15mm target around each hole, and I have an engineer that's wanting me to also specify an inner diameter of ∅13mm for the target area. So the datum call out would have ∅15-∅13 in the top half of the circle. I can't find anything in the book that says you can do this, nor can I find any past drawings in the company that calls it out this way. so, I have a two part question.

1. Is it allowed to specify an inner and outer diameter for a target area?

2. If this is allowed, how would you interpret the call out? To my thinking, I would have to make a ∅1mm pin sit inside that ring defined by the ∅15-∅13 dimensions.

Thanks everyone for your help.

 

[Belanger]

To do that, I would just dimension the two rings on the drawing (as diameters with basic dims) rather than trying to squeeze two parameters into the upper half of the datum target symbol.

(Edit: I just noticed that your two diameters are so close together -- a radial separation of only 1 mm. They don't have to be drawn strictly to scale. I'm now wondering why your colleague would want such a small area. Oh well.)

 

[jake.]

Hi destes,

1. Is it allowed to specify an inner and outer diameter for a target area?

Assuming you are working to the 2009 standard:

4.24.4 (p. 85) "Where it is determined that an area is necessary to assure establishment of the simulated datum (that is, where spherical or pointed pins would be inadequate), a target area of the desired shape is specified."

I would detail both diameters of your target area explicitly.

2. If this is allowed, how would you interpret the call out? To my thinking, I would have to make a ∅1mm pin sit inside that ring defined by the ∅15-∅13 dimensions.

I believe the datum feature simulator would mimic the prescribed datum target area, just like in the case of a circular or rectangular area.

Jake