Two-Point Distance at LMC

[[Ja...]]

Per ASME Y14.5 rule 1 (UOS, size controls form and perfect form at MMC), how is this done when a feature of size requires perfect form at LMC for a pair of parallel planes?

I've used the two-point distance and two-point diameter tool with envelope condition to account for rule 1 at MMC, but can these tools be used to account for perfect form at LMC? If so, how? Or is there another way?

Two-Point Distance.png

[[Ro...]]

For symmetry planes you can report the distance inside the feature itself. In the created characteristic you can change the evaluation settings for the feature by clicking on it and changing it below. Use inner and/or outer tangential to report the boundary of the feature, depending on your needs.. i.e. if it's an outer or inner width you need the result for. As long as it's inside the min and max boundaries it satisfies the envelope rule.

[[Da...]]

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That's not correct. If you want to evaluate the envelope condition (Rule #1) on a slot, you need to check the inner tangential plane of one plane to the high point of the other plane parallel to that inner tangential plane for the minimum tolerance.

The maximum tolerance must be evaluated per 2-point-distance, which I believe, Calypso cannot do at the moment for opposing planes. If you used the outer tangential planes for that, points that are not opposing would be used, which would clearly give false results, usually a distance too large and probably OOT.

Stupid me, of course the 2-point-distance should cover opposing planes, what was I thinking... Don't know why it wouldn't work in Jarret's example. Maybe he should see that the nominals of the planes are correct.

[[Ro...]]

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Isn't that what inner and outer tangential are doing? Same as using Max/Min inscribed/circumscribed on a cylinder? Isn't it calculating the max/min cylinder at perfect form? Isn't using tangential planes doing the same thing? Similar to a expanding/contracting mandrel of perfect form?

[[Ro...]]

Here's my opinion, for what it's worth.

You are correct. 2-point distance will give you the min/max of opposing points.

But it doesn't consider form or the mating envelope. You could have 2 planes that were warped, but as long as they're warped symmetrically, 2-point distance will say that they are fine. This is why I rarely use 2-point distance and am ignorant about what it does or it's usefulness. I only use it to satisfy legacy drawings requiring 2 point bore gage measurements.

Tangential isn't measuring opposing points. It's using expanding/contracting perfect geometry to report the mating envelope. This is what i normally use, because I need to know if the part will function or not, and form controls are normally applied to geometry that needs to have it's form tightly controlled.

So yeah. You are absolutely correct. Thanks for the information.

How did I do? 😐

[[Ja...]]

See graphic for better explanation of what I'm struggling with.

Size LMC or MMC comparison.png

[[Ro...]]

That graphic sums it up perfectly. I guess it all depends on what result you want and/or how the part is being used.

What does 2-point report if you don't use envelope condition?

[[Ja...]]

If I use "two point distance dim." rather than "envelope condition" setting, it will give worst case minimum and maximum apposed point sizes... So I guess this could work in a sense to get worst case largest local size, but we would have to ignore the minimum distance size on reports and add an additional caliper size or maybe distance symmetry to get an inner tangential size.
That would give 3 results in all, but we only need 2 of them.

[[Da...]]

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Yes, the inner and outer tangential is doing the same for planes as max inscribed and min circumscribed for cylinders, but for cylinders the envelope condition is not evaluated by using the MIC and the MCC at the same time. For a hole it‘s the max inscribed (you can also choose the outer tangential) for the minimum tolerance and the two-point distance for the maximum tolerance, and for an outer element like a stud it’s the min circumscribed (also outer tangential) for the maximum tolerance and the two-point distance for the minimum tolerance.

So, the envelope condition only needs an envelope on the maximum material side, which is always the outer tangential element.

[[Ro...]]

Jarrett... That's kind of what I was thinking. Use 2 characteristics and pull the needed result from each. You could create a result element for each one, pull the info you need into it, and mask the original characteristic. That will give you 2 results.

[[Ro...]]

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Thanks, Daniel. That explains a lot. I appreciate the discussion. 🙂