Pattern of slots as Datum

[[Wo...]]

Datum "C" on this print is the pattern of slots. They are equally spaced around Datum "B" (a cylinder).
Datum "A" is a flange plane.

How would I go about checking both Position #31 and #34 ?

I don't deal with slots too much so I'm stumped a bit.


Any suggestions welcome.
Thanks,
Wojciech

Edit: More details: The print is ASME Y14.5-2009
The basic dimension "11.3 degrees" is rounded up. In reality it's 11.25.

[[Ch...]]

you could do a best fit to your pattern of symmetry planes, however you may find better results by "transforming" the slots to circle,

and only allowing the best fit to 'rotate'

This best fit essentially becomes your -C-. ( which is actually A|B+C)

TIP : if you need to reference this clocking of -C-, you can recall the best fit as an alignment in your position,

However if you want to position to B|C, Primary =B Secondary = B Tertiary = a theoretical 3 D Line in the plane normal to -A- (whose center is -B-, and direction is 12 o'clock on the drawing for example). If this theo 3d line's alignment is the Best Fit, it satisfies the -C- pattern rotation in my opinion.

There may be other ways as well.

[[Wo...]]

Thank you Chris,

It's along the lines I was thinking. Except of transforming slots into circles.

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I'm not sure how would I create the theoretical line aligned to Best Fit ?

Thanks,
Wojciech

[[Ch...]]

After youve done the best fit,

create 3d line X+Y =0 make it a random length , = 1.0" along a nominal axis , X or Y, then simply by changing its alignment to the 'BestFit' Alignment this should be a line on 0° of the rotated Best Fit, provided the 3d line angles are 0,0 and it lies on an X/Y axis etc.

[[Wo...]]

Got it, thanks. I did not realize you can choose Best Fit as alignment in the feature window.

So far I've created a pattern of symmetry planes and created a best fit of that.

Set it up as pictured, but applying Position requirement directly to it was not successful.

I was thinking of evaluating each Symmetry Plane to a separate Position requirement and rotating DRF with "Special".

But then, what would the DRF itself look like? Just AB? In that case each slot would be evaluated independently of each other and I doubt that's the correct way to do it.

Thanks,
Wojciech

[[Ch...]]

It depends on your spec regarding evaluating the pattern independently.
For ASME by default they apply as a SIM REQT, per ISO it is the opposite, it applies INDIVIDUALLY rather than simultaneously.

Looks like your spec is ASME, so using the best fit for all slots covers the SIM REQT for rotation.

Yes you can use this best fit for recall in other alignments and even features. You'll find with more complex GDT you will need to.

Good luck.