# Tab to circle True Position?

S

#### s529f

Hi guys,
this is always a problem for me conceptualizing and I decided to finally try and get some help. I get a lot of prints coming through with tabs, slots, punches, etc somewhere along the radius of a circle and then called out with a true position to the circle but with no other refrence to use as a datum for any angle or something. I have no idea how to get a number because it seems like if its along the circle its ok, or is it that the centerline of the slot has to be straight enough to pass through the center of the circle? I can't attach a picture apparently because i havent made enough posts but it is like this (pretend the pointy thing in the middle is a hole and the angled thing is a circle on the od)
_
....| |...
/::::/ \::::\
/:::::| |:::::\
|:::::| |:::::|<------7.5+/-.003
\:::::| | ::::/ V_
\:::::\/:::::/ |-A-|
|_|
^.40+/-.002
|TP|.002|A|

#### Michael_M

Trusted Information Resource
If I am understanding correctly, it looks like they want the tab or slot within .002 true position to the OD diameter of the part. If this is the case, then simply measure from the edge of one side of the slot to the outside diameter and then repeat doing the same thing to the other side. The difference between the two readings cannot be more then .001.

To get a number to record, find the difference between the two measurements and multiply by 2.

I hope this helps.

S

#### s529f

so it doesn't have anything to do with the angles or anything? That makes sense, thanks!

#### Michael_M

Trusted Information Resource
The call out is to 'A' which appears to be the OD of the part. There is no secondary or tertiary datum call outs (and against a round object, would be a bit more difficult to get).

Without a secondary or tertiary datum point, they are just asking for location without regards to any other datum points.

I found this on the internet looking to spelling "tertiary". It's from the 1994 requirements but may help.

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