GD&T re Hex shaft with 2 different Hex sizes

[Happyfeet63]

I am an ME, now disabled, working from home (95% for my 35 yr. career was spent in mfg. mgmt. – so I am very rusty) and am designing a drilling center for drilling a hole in ea. side of a Hex coupling nut (simultaneously). Need a bit setup gauge for bit changes in the drill heads utilizing the pic & place system. It has 2 sizes of Hex on the same short shaft. Need to Tolerance this for making the sides of the 2 Hex sizes within certain degrees of each other around the center axis. Do not know quite what nomenclature to use in the FCF.

Any suggestions would be appreciated!

Thanks,
Larry

 

[JNieman]

1) Remove the word "bit" from everything. The cutting tools are called drills in a machining environment. Carpenters call them "Drill bits" ("#31 Drill" instead of "#31 Drill Bit")

2) "Bit Point -0.25" should be "DRILL CENTER .25" (There are no negative distances. Distances are absolute values. Coordinates can be negative, not linear values.)

3) What's the purpose of the larger hex size?

4) Look into "Parallelism" or perhaps "Angularity". I believe "Parallelism" would be more appropriate.

_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

 

[Happyfeet63]

Thanks for the FYI re: "drills" (FYI, when I was physically able I was an avid woodworking hobbyist and the use of "Drill Bit" I suppose has crept into my vocabulary). . The notation on the drawing of "Drill Center" is not a negative symbol but rather a "Tilde" (~) which in "Elizabethan" time (a little humor) meant approximately (I used that instead of approximately (or an abbreviation thereof) which I probably should have). The purpose of the larger Hex is as follows: The gripper holding the nut has a very limited travel and are sized to grip a 0.625 AF Hex nut; thus the larger end of the gauge is sized to fit in the gripper; the purpose of the smaller end of the gauge is so that the drill heads, when the drills, are changed can be set at the extended end of their stroke and thus eliminate the possibility of the "Drills" colliding. As a simpler solution I might re-spec the gripper so that 2 Hex sizes are not needed.

Thanks for you input, it has been very helpful and has caused me to rethink the design in order to simplify the gauge.

Larry

 

[Happyfeet63]

In the revised drawing, I want the small hex of the gauge to be parallel and within angular tolerance in relation to the large hex. Do the GD&T specifications appear reasonable and measurable?

 

[geesamand]

Shooting from the cuff..

GD&T datums are always based on a functional gauge. Just because there isn't a predefined symbol for your situation does not mean you should limit yourself to the symbols. Besides if there is an exotic callout and the reader doesn't understand it, it does you no good.

In this case, I would consider declaring a datum axis as being the centerline formed by a "three jaw" hold on one hex (preferably the narrower, longer one), and then limit the distance from that centerline to the faces of the other hex. That will control both overall size of the second hex as well as the centering of it.

Then it's a matter of applying size dims and parallelism tolerances to the faces of the "datum" hex.