locating a slot to a flat surface? 1

[JordonMusser]

In this part the only critical dimension is that a plane that goes through the axis of the part, and the center line of the slot is perpendicular to the flat that is machined on the right side of the part.

any ideas on how to represent this? The function of the part is that the "flat" is a datum for calibrating(in rotation) the location of the pin that would go in that slot. So if that slot(and thus the pin that goes in it) is exactly TDC, the flat would be exactly 90*.

 

[powerhound]

If you call out the features WRT the same datum structure then the Simultaneous Requirements rule is in effect. That has been a much discussed topic recently. It is up to you to determine how much tolerance is allowable because "exactly" is not what youa re going to get.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
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[drawoh]

JordonMusser,

Talk about imaginary planes is confusing. I take it you want the slot to be perpendicular to the flat face, and you want the slot's width located accurately to the diameter.

The main problem I see is that your slot is small. Even a tight perpendicular control could allow a significant angular error.

To which of the diameters shown should be slot be centred? The outside diameter would be the easiest to fixture to. Since this is a feature of size, an accurate feature is preferable for fixturing. Datum_A.

I would use the flat face as the secondary datum Datum_B, and one of the ends as the tertiary datum_C.

The tolerances I applied would depend massively on the relative accuracy of the slot location and the slot perpendicularity.

JHG

 

[drawoh]

JordonMusser,

I just had a second thought here.

Does the slot have to be perpendicular, or does it just have to be centred perpendicular to the flat face? If this is the case, a true position tolerance applied to the slot width, should do it for you.

JHG

 

[JordonMusser]

I need it essentially centered to the perpendicular face.

imagine a shaft with the exact same axis that is keyed to the above part with a pin in that slot. I need to have a defined relationship between the potential angular error.

 

[ringman]

What if: the OD were A, the flat B and the width of the slot were positionally toleranced to .000 at mmc to A and B

 

[powerhound]

Per the simultaneous requirements rule you can position each of them WRT to A with A being the OD and the features will have to be produced as depicted and meeting their tolerances simultaneously. The features are considered a pattern by default per the standard.
As I said before we had this discussion a few weeks back and I referred to this link:

http://www.tec-ease.com/tips/feb-08.htm

Also here:

http://www.tec-ease.com/tips/january-00.htm

Hopefully this clears the simultaneous requirements rule up. I'm pretty sure one of these examples is in the 2008 release of the standard but I don't remember which one.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II