Brain freeze. Sanity check only

[Kedu]

My question has nothing to do with the current weather, nor with the polar vortex. For some (unknown to me reason) my brain got stuck in its own paradigm.

In fig 4-4/2009 does the mutual relationship between 6 holes (7.1-7.3) to the left and 4 holes to the right is being controlled? Otherwise stated, could the 4 holes to the right of the flange be clocked at any angle relative the 6 holes to the left?

Datum feature D is contolled back to A and B respectively, but that does not ensure the clocking between the patterns, correct?

 

[3DDave]

That is right. There's no limitation on the mutual orientation of the hole patterns around the nominal axis between the two ends.

 

[greenimi]

3DDave and all,

The "clocking" issue has been touched before on this forum, I don't remember the exact thread/ discussion, but I would ask you and everyone else on this forum, what would be a potentially good solution(s) to enforce the clocking between the two sides.
Solution 1: Add another position to the 4 holes to the right to A|B
Solution 2: Make one of the six left holes a datum feature (lets say datum feature E) and then adjust the position of the 4 left holes to C|D|E

Any agreement/disagreement with my solutions?

Also, any other solution you can think of to limit the mutual orientation of the hole patterns?

Thank you for your input

 

[CheckerHater]

Create multiple single-segment position for holes.
Second segment being position wrt compound datum B-D

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[mkcski]

Add a nonfunctional feature to control the rotational orientation and assign it to the FCF in both ends.

Certified Sr. GD&T Professional

 

[greenimi]

Add a nonfunctional feature to control the rotational orientation and assign it to the FCF in both ends.

mkcski,
May I ask for more details about your proposed solution? What do you mean by "nonfunctiona feature"? Add another hole/ slot/ boss to the part (potentially increasing the cost per piece) or use make an existing feature as I proposed in my solution 2 or something else you had in your mind?

Just confused.

 

[Kedu]

Thank you all.
May I ask, what would the the advantage of choosing one hole (one of the six left holes at random) to stop the clocking versus choosing the pattern of the six left holes?
Which is the preferable way?

I understood from the previous replies that 4 right holes to A and B is more like a "fancy" way to ensure clocking. When would you use it?

 

[3DDave]

You need less sophisticated fitting software if only one hole is chosen, but it might take longer to find the one hole that allows meeting the requirement. In this case, being as there is a mutual prime ratio (2) that means only two potential positions, but if it was 6 on each end, then there would be 6 to try.

 

[mkcski]

greenimi:

I was thinking of a small hole in one of the flange faces, or maybe a flat surface on the OD of either end-flange. Basically, a feature that would be easily accessible for Mfg and for QA.

Certified Sr. GD&T Professional

 

[greenimi]

mkcski, (and all)
Well, I will just post one of the quotes from a previous threads:

Yes, if the datum hole C does not play any physical role in how the part is oriented in assembly, then the drawing defines more restrictive geometric requirements than they need to be (although based on experience I would say that to make everyone's life easier, it is sometimes better to define a "clocking" datum feature, even if it is not a function-based choice).

https://www.eng-tips.com/viewthread.cfm?qid=428041

Now, I am not sure pmarc really (really......) is stating that a few NEW feature should be made/manufactured just for the sake of "clocking" -- to make the life easier down the production/inspection line....---or he meant using an existing feature.
Here is a case where if we are not careful in the design the "horse will jump the fence" (or should I say the horse is out of the barn) and a truly functional approach (simultaneous requirement) quickly turns in a non-functional one (at least for some features)

pmarc,
Could you, please clarify? I am just trying to learn from your experience and knowledge.

Thanks again

 

[Kedu]

So, still confused, why use clocking then? Looks like either MMB or RMB for the tertiary datum feature does not bring any advantages, unless I am missing the mark here.

 

[chez311]

Kedu,

Maybe you could expand on your question? Your initial inquiry was "is there a requirement for these features to be clocked/held relative rotationally to each other" - the answer was no, and then several potential solutions were presented if you theoretically wanted the requirement, this is the "why".

Are you actually asking about the advantages of inclusion of a tertiary datum feature vs. simultaneous requirements for clocking? Or something else?

 

[Kedu]

Re: "
Are you actually asking about the advantages of inclusion of a tertiary datum feature vs. simultaneous requirements for clocking? "

Yes, sir. I would be interested in that. Appreciate your patience.

 

[3DDave]

Already covered:

You need less sophisticated fitting software if only one hole is chosen, but it might take longer to find the one hole that allows meeting the requirement. In this case, being as there is a mutual prime ratio (2) that means only two potential positions, but if it was 6 on each end, then there would be 6 to try.

 

[chez311]

3DDave,

Wouldn't the same be true if the entire pattern of 6x or 4x holes was chosen as a tertiary datum? Or even if simultaneous requirements was utilized?

Additionally it seems to me that while there might be effectively no difference in simultaneous requirements vs. tertiary datum feature reference for MMB/MMC, there could be for RMB/RFS. Wouldn't setting one pattern (or one hole of one pattern) as the datum feature be tighter than simultaneous requirements in that case as any variation between the features would be amplified because the datum feature would have to be oriented first?

Also something to keep in mind is the suggestion of creating a non-functional feature means the creation of additional geometry, possibly added cost, and the necessity to hold a non-functional feature to a sufficiently tight tolerance so that other features can be referenced from it - ie: whats unimportant (or of no importance/consequence) to part function becomes important for inspection.

 

[mkcski]

All:

Let me chime in again. The cost of a machining a tertiary datum must be compared to the cost of (more) difficult inspection and not having a repeatable origin of measurement. In this case, something as simple as a small flat surface on the OD of one of the flanges will suffice. Since a flat surface has no size, the MMB/RMB issues disappear. Assuming the milling cutter is already "there", the cost of milling the flat is minor.

Certified Sr. GD&T Professional

 

[greenimi]

mkcski,
My point is: any feature, does not really matter how small it is, cost money.
Why to make something special for inspection only, when you already have some features you can use?
The question seems to be: do you really need to use that existing feature or you get get away without? And what are the consequences of either scenario?