Tapered Hex Pin Datum Setup 1

[Angle C]

Building upon what I learned from pmarc and others in thread1103-360909 relating to datum referencing tapered faces of a part, I attempted to construct the attached drawing. This is a tapered hex pin. I don't feel this drawing is adequately specified, and I have these following questions.

1.) I did not reference any datums in the surface profile callout. It would seem to be a circular reference if the profile tolerance of datum feature A or B referenced datum plane A-B. If I understood correctly, I believe pmarc more or less stated this in different words in his post in the referenced thread above. But perhaps it could/should reference datum C. I could use some other opinions here.

2.) I have specified 3 sections with distances across flats. With the basic included angle of 0.5 degrees I supposed 1 linear dimension across flats is all it would take. I could make the others references. The function of this part is to slide into the cored region of an injection molded lead screw and gear and transmit torque between them. Therefore, having reference dimensions across various sections is a helpful check on the fit.

3.) The principles of drawing standards give one a lot of information for free as a lot can be inferred. I wonder if the information in a drawing like this automatically implies these dimensions and tolerances apply across any 2 flats, without explicitly stating this. If this is not called out in a note, I suppose a supplier could claim the check was made across a single pair of flats. What is the easiest method of accomplishing this, or is it not required as it is implied? I would hope one wouldn't need to create 6 unique lettered datum surfaces for the hex.

I'm a novice at this, so all feedback is very much appreciated.

 

[Sem_D220]

Assuming drawing standard ASME Y14.5-2009,
A few thoughts:

* As you noted, basic 5° on the taper + 3 dimensions across flats = more dimensions than necessary. Make 2 dimensions across flats reference.

* Datum features A and B are not used in any controls, therefore, can be removed from the drawing. The profile call out can reference C to ensure proper orientation.

* Using profile all over communicates that you intend to apply the tolerance zone all over the part, but the separate directly toleranced dimensions on the other features such as the different radii suggest otherwise. If I am not mistaken, all around suits your described intent better.

* To indicate that your tolerance zone applies for each couple of opposed flats you should probably add another leader from the profile FCF to the bottom flat in the view (and show the unilateral tolerance zone there too), and add 3X before the feature control frame.

* I think others will tell you that combining directly toleranced and basic dimensions in a drawing is not recommended.

Other than that I am interested to read what the general opinion is about dimension 2.85+-0.05 to the end of the radius 4.00 from dimensioning standpoint. Where I work such dimensions are often given and inspection is often possible with optical measurement equipment (even though probably not very accurate), however para. 1.4 in ASME Y14.5-2009 (FUNDAMENTAL RULES) states:
"(g) Dimensions should be arranged to provide required information for optimum readability. Dimensions should be shown in true profile views and refer to visible outlines.". The thin line connecting between the radius and the flat is visible on the drawing, but not on the actual part. Is this considered valid?

 

[pylfrm]

Angle C,
[ul]
[li]Is contact with the gear and screw intended to be made only on the six flat tapered surfaces, or also on the six curved surfaces connecting them?[/li]
[li]Are those six curved surfaces nominally cylindrical, or conical?[/li]
[li]What is the intended function of the features / surfaces at the ends of the part?[/li]
[li]Are there any other aspects of the functionality you haven't explained?[/li]
[li]Which drafting standard are you working with?[/li]
[/ul]


pylfrm