Phantom Datum on a Product Design Drawing

[learningchecker]

Hi,

We are using ASME Y14.5-2009. This is a MIM part (mold). Our Design department's final checker is a Manufacturing Enginneer. He has REDLINED a part that I don't fully agree with, but I could be wrong. Please HELP.

The base of this part is critical to fit. Two opposite sides are angled with a long "bump" on each side for an interference fit. The "final checker" has chosen to add another phantom dia gage pin on each side, just up from the bumps, to create the angle. So, each phantom pin (.100 dia.) is about 2 inches apart measured at each center. He has a dimension from inside tangent to inside tangent of 1.900 ±.0015 and that dim. is Datum G. The inside tangent is inside the molded part which is filled with material. In true position FCFs on other areas of the part, he does reference DATUM G.

Is this possible or even legal to do? DATUM G is not a feature on the part and is also inside material. Not making sense to me.

PLEASE HELP. Thank you.

 

[3DDave]

It sounds like a datum target scheme, but even those are required to apply to a particular surface. For example, in measuring spur gears and screw threads, it is common to use wire of a certain diameter to aid in using a caliper to make the measurement. However, this wire is not shown inside the part, but tangent to the related surfaces. Maybe he's just a bad sketcher.

Can you post a picture that represents what you have and also what you want?

 

[TheTick]

Manufacturing engineers like to make designers do this sort of thing, because they generally don't like to do their jobs. Let the gage designers design the gage.

 

[learningchecker]

I would love to have the tool designers design the gage, but he is "LAW" and will not take "NO" for an answer. That's why I need to have a valid reason he shouldn't do this.

I hesitate to send an attachment because of propriety reasons because I'm a contractor.

 

[learningchecker]

Nope, not a bad sketcher. It's very clear.

 

[3DDave]

If you are a contractor, then easy - keep a copy of the markup in a safe place, give a copy to your boss or whoever told you to do this work (flatly stating this is the markup, should I do it?), and (if yes) just incorporate the markup as-is.

I've learned it's OK to care, but it's not worth it to worry.

 

[KENAT]

So is it really an equalizing datum type situation, but rather than going back to setting up the appropriate datum target scheme he is as others suggest effectively drawing in what he thinks will be the inspection set up?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[pmarc]

I would love to see a picture too. Perhaps you could send something simplified?

 

[learningchecker]

Yes, to KENAT. He and the engineers here do that way too many times. They want to enforce the inspection there way. Also, with this problem, the parts are not coming in to print and not working properly, so this is his solution eventhough it hasn't worked in the past.

If I can make the time and the comfort level, I'll send in a picture.

 

[learningchecker]

Sorry, they want to enforce the inspection "their" way.

 

[ewh]

I would do as 3DDave suggests. One of the joys of contracting is, after doing your due diligence, to act like a duck and let such issues just fall away like water. If it were a direct position, I would perhaps fight back a bit more. In the meantime, treat it as a lesson learned.


“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[learningchecker]

Very hard for me to do, but I will just relax and let it gooooooooooooooo.

Thanks everyone.

 

[TheTick]

Add a note to the drawing along the lines of "Sound engineering practices and standards abandoned in favor of abhorrent hacksmanship".

 

[learningchecker]

I love it. Sounds good to me.