Tripple stacked True Position

[dtalco12]

I have a call into the design engineer but I wanted to see if anyone else has run across this.
I have a call out that is 3 True Positions stacked on top of each other. See attached.
I am familiar with the double stacked version, but I must admit I do not know what they are getting at with the 3rd.
They have gone far enough to designate both diameters as Datum -B- so is the third TP intended to be for concentricity between the 2 diameters?
Datums -D- and -J- are cylinders on the other 2 axis' that -B- is not on (if that helps any).
Please advise.

 

[fsincox]

Yes, This kind of thing is now shown in the newer standards, even as a composite, that was the real question!
Frank

 

[powerhound]

The lowest segment is controlling the coaxiality of the two bores to each other, independent of any datums. The upper segment centers the axis of datum B on the intersection of datum planes D and J within a diameter of .005. The middle segment tightens up the location of datum axis B to datum axis D within .002 but datum axis B is still free to translate along datum axis J within its .005 diameter.

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

 

[drawoh]

dtalco12,

I have no objections to triple stacking. The part must meet all specifications.

I do not understand the third specification. Testing the two bores for co-axiality looks impossible to me. Each bore is 2mm long! How are you going to find the centre-lines?

--
JHG

 

[powerhound]

To check coaxialty of the holes per the lowest segment, you would first check to make sure that each cylinder meets its size requirement then if you can fit a .9444 diameter, gage quality, pin through both bores simultaneously, then the coaxialty is in spec.

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

 

[bxbzq]

John,
If I understand the drawing correctly, a dia .94444 gage pin won't go through the hole. There are two dia. (.908, .918) bores.

By the way, the nominal length of each bore is .324, meaning 8.2x mm.

 

[powerhound]

Yes, you are correct, I didn't notice that. The alternative is a two piece gage where each piece enters from each end and interfaces somewhere in the middle. There are other ways to check this as well. It just depends on what you have available.

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