How Does the Demon Use Bonus and Datum Shift When Reporting?

[Darrollh]

How does PCD use the bonus and datum shift? I had a part that's right according to the report but the engineer think it's a mistake. I want to be able to explain this to her so I can put this to bed!!!!

[vpt.se]

Datum shift (from (M) on datums) is used for (larger) "wiggling" room when fitting to datums.

Bonus (from (M) on features) is used to enlarge the tolerance zone depending on the features size and tolerance.

[Darrollh]

What about using the S modifier?

[AndersI]

"Regardless of feature size" - it's the same as no modifier.

[MikeD6]

Just FYI, you may already know this but I'll say it anyway...If a part is in spec without using a datum modifier, then it will be in spec with, 100% of the time. In my experience they're usually more trouble than they're worth.

[Darrollh]

II am catching some heat because the part looks like its out of tolerance but the report shows it to be in tolerance.

[Schlag]

Right. If you have MMB ( or MMC ) and decide not to use them, you will never accept bad parts, but you could be rejecting good parts.

[bfire85]

Also make sure you have the correct tolerance on the datum so the correct shift gets calculated.

[MikeD6]

It looks out in what way? Form fit or function? Or are you reporting out with legacy and Xactmeasure and they're conflicting?

[KIRBSTER269]

Darrollh make sure your Datum structure makes sense also. Or you could end up with sh_it like this. because of pi_ss poor engineering.

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[Darrollh]

That's exactly what I have!!!!!!

[MikeD6]

Are you trying to explain how datum shift works to your engineer or how PC-DMIS does it?

[KIRBSTER269]

Arguing with an engineer is a waste of time, even if you show them proof. They don't believe you, because they THINK they don't make mistakes. Ask them the formula for Position.

Here you might have better luck with this.

25c18737598b6e6b415f6bb585640079[1].jpg


How about this, Tell Her, I just showed you its BAD, How about you go show me on the Surface Table, Lay It out, and show me it's good!

[KIRBSTER269]

Is there anyway you can share the Datum structure or even the print and callout?

[oddam]

Do you have a check fixture to place the part on, clamp it, pin the feature that is in question? I try to use a check fixture for part measurement as much as possible. If PCD reports something out, it should be the same on the fixture. There are many times where the positional pin will scrape the edge of the measured feature, that can be the edge of acc. or reject with PCD.