Dual Datum Structure

[[Do...]]

Has anyone seen these types of callouts before? How does one set up the alignment to measure these or even replicate the dual datum usage?

Screenshot 2023-05-01 105910.pngScreenshot 2023-05-01 105939.png

[[To...]]

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Depending on how long the feature is one each end, create either a cylinder or circle on each end. Create a new cylinder feature from the Features menu. Open the cylinder, under options, select Recall Feature Points. Select the two cylinders/circles. Click OK. This cylinder is now Datum Feature A-B.

I think I would now create 2 new features on each end and check their positions to the A-B cylinder. You will likely not be able to take advantage of MMB on A and B but you may not need it. Maybe someone might add something to this.

[[Do...]]

Thanks for the information. I will surely give this a try.

[[Do...]]

I guess I forgot to mention that these two ends are not aligned with each other. There are actually a few bends between the two ends. Would I still do the cylinder that recalls the feature points from the circle or cylinder at each end?

[[To...]]

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Details, details, details....lol

This might be a good application for a Parallel Cylinder feature (Special Geometries). Not sure. I haven't tested this completely.

Create 2 cylinders. Create Parallel Cylinder. Recall Feature Points from 2 cylinders. On the Diameter tab, click the D and set the tolerances.

Create 2 Positions, one for each cylinder, using Parallel Cylinder as Primary Datum Feature. Activate MMC on both the feature and the datum feature. Maybe this will work.

Leave it to the forum to expose gd&t that I've not seen before....

[[Zo...]]

I have similar drawing that we work with,

A-B is a line based on GD&T

instead of recalling feature points, just recall features.
this will create the proper datum A-B

in my case i have an cylinder as B and cone as A

[[To...]]

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Even though the poster's application is not an inline axis, according to Y14.5, a line won't let you apply MMB.

2 inline datum features A-B 2.jpg

[[Ma...]]

Stepped cylinder should work with MMB

[[To...]]

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Hello Martin,
A and B are not in-line.

[[Ma...]]

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I saw a position in stepped cylinder feature - is it used only for position callout?

[[Zo...]]

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honestly, i am i bit confused with M inside reference datum box.
correct me if i am wrong but a Datum doesn't change with size. they are supposed to be outer-tangential
if datum A is a cylinder of 10mm diameter or 20 mm diameter it remains the same in terms of its effect as datum

also, A-B is an axis and axis don't have Material to be in max or min, as you mentioned

now, another issue with this drawing is, Datum "A" diameter can be running out to an axis of A-B, but always be in perfect true position as long as there is no plan as primary datum

for example |TP|dia6.0 A|C|A-B| where C is a plan perpendicular to A-B

if there are no planner datum, it should be

|runout|0.05|A-B| for both tolerance boxes, A and B

[[To...]]

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Yes, if A and B were concentric. On the poster's part, they are not.

Also, step cylinder would not be necessary if both diameters are the same. If both diameters are the same, a standard cylinder would work.

[[Zo...]]

after typing my last reply, i just went back and realized the two A and B are not in Line 🙂

now that is nothin g i had seen before but seems like there is GD and T explanation for it

this is what i could find



i am not sure how you can enforce this in Calypso, but at least should give you a visual as to what you are trying to achieve

i will keep looking

[[To...]]

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M on a datum feature does not get additional tolerance but allows movement or "datum shift" . For example, imagine a gage with a bore made at the Max Material Condition size of the Datum A feature. And, again for the Datum B feature. The Datum A and B features could wiggle back and forth in gage in order to make the considered feature(s) fit.

If you just create a 3d line and recall the 2 cylinders, the line is generated from the mid-point of the 2 cylinders and the size of the cylinders have no impact, so the M cannot be utilized in the evaluation.

I think the 3d line would probably be ok if there was no M as long as the 2 cylinders were evaluated using OTE.

[[To...]]

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See my post at 7:55am

I believe I might have come up with a solution using the Parallel Cylinder feature in Calypso. It creates a datum structure from the symmetry of two cylinders.

[[Zo...]]

i managed to create most of it,

however, i still believe "M" condition in A-B is not allowed
there is definitely no option in Calypso for it



other than that, i was able to create two Cylinders and create a symmetry
than use it to get true position for each in M condition

[[To...]]

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Go to features menu > special geometries. Select Parallel Cylinder. Recall Feature Point from 2 cylinders. Make sure to set tolerances of cylinders in Parallel Cylinder

[[Zo...]]

not happening for me 🙂

[[Zo...]]

Finally found a source _which proved me wrong_ that explains it

https://www.faro.com/en/Resource-Librar ... eature%20B

[[To...]]

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I see you're on 2018. I think Parallel Cylinder came out in 2020 or 2021. So, a symmetry of the 2 cylinders seems like it may work, though with no MMB.

[[Do...]]

So here is a better example of the type of situation I have. How do I set up and define A(M)-B(M)

Screenshot 2023-05-11 160359.png