surface profile with two datums

[[Ja...]]

Hi Guys,
I have a cylindrical part with 6 bores in it. The top surface is datum A, OD is datum B. Now, I have to measure the surface profile of these bores with datum A and datum B (no tertiary datum). This means that it is asking for these profiles irrespective of orientation.
I have used several approaches after reading some posts on the forum:
1) Using respective bores as tertiary datum for each of their profile but DRF seen in calypso window doesnt seem to orient itself with the bore and still gives out a result
2) Using intersection points of each bore with top surface datum A as tertiary datums for each profile, DRF does orient itself to the bore and gives out a result
3) Using Utilities > Alignment to create alignment using Datum A for planar rotation and Z origin and Datum B for X and Y origin referring to Base Alignment and then use that alignment for another geometry best fit alignments for each bore and rotation about Z axis as constraint in them. DRF doesnt seem to orient itself to the bore and also gives a result.
None of the method seems superior to other in terms of the results of surface profile.
Any suggestions on how to work on this or a preferred method?

[[Me...]]

What's the callout on the print?
They probably have simultaneous requirements, which means they need to be checked in the same alignment. If they want Profile and not Position, you could measure them as curves and use Alignment from Several Curves, allowing them to rotate about the axis as a group. Then copy and recall the curves into new curves, put them in the best fit alignment, and report their profiles.

[[Ja...]]

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For these bores, the only callout are [ surface profile | 0.010 | A | B ] and another callout is [ surface profile | 0.020 | A | B | C ] where datum C is a slot on Datum A to lock spatial rotation of the part (I probed one of the side plane of the slot as Datum C instead of using Symmetry plane on both sides of slot as Datum C ) there is no other FRF for these bores called out on the print

[[SH...]]

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If my intuition is correct, it should be a true position with pattern.
Profile is very expensive tolerance, lot of companys don't have free form and curve.

[[Er...]]

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What are you on about??!! More profile tolerances to the world! It's in many cases (not all) the only thing you need.

You should not take any consideration to if some one have, or not have a license in thier CMM/Measurement equipment when designing a part... Toughts like that will have a bad influence on ingenuity. Epecially in this time of age with all additive manufacturing going on.

PROFILE FOR PRESIDENT!

[[Ro...]]

Years & Years ago i had a very thin tube with cross drilled holes. There was also no repeatable way to fixture the part, so we used a 3 jaw chuck and a calibrated eye ball to visually align the part.
I think our dims were a true position to the end and the center of the tube, but like your situation there was no rotational requirement, but just to get a good reading we had to adjust for rotation.
The final solution was to create a couple points on the cad model then massage them to locate them inside the part, so when they were probed the stylus tip would actually make contact with the shaft, not the ruby. This gave us the best results.
We probed 2 points at the same Z on either side, then created a symmetry point and a 3D line that would serve as rotation.
It could also be done with circles instead of points.

Then finally we could probe points on the cross hole that would be constructed into a cylinder,
then constructed into 2 intersection circles with the OD skin,
then constructed into a symmetry point that would theoretically hang in the exact center of the part.

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[[Me...]]

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Agreed. There are some very compelling arguments that propose using profile for virtually everything in a drawing. You can control just about everything with it if it's applied correctly. Unfortunately, it's often used as a catch-all in a drawing note for undimensioned features, or not used where it should be used in place of position.

[[Ja...]]

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My problem is not with base alignment of the part. I have a working program and it scans all datums and bores without any problem. The issue is to use only two datums for surface profile results. I am trying to solve it by using the feature itself as tertiary datum or making a different alignment using geometry best fit and still cannot make sense of which result to believe.

[[SH...]]

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while designing a product a product designer must emphasize on method of inspection and method of manufacturing that is what is called DFM.
according to OP'S words his job does not deserve profile,it can be accomplished by position.

Profile should be only used for complicated shape that cannot be controlled by true position..

[[Er...]]

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No, that is not a job for a designer. He only needs design the part, that fulfills the task assigned. And usually he/she/it also specified tolerances that shall reflect functional limits. (But on complex designs this is many times done in cooperation with "experts" in different areas. Such as air flow engineers, vibration experts, etc. etc.
Leave inspection methods to us, the "metrologists".

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This is better suited for manufacturing engineers... Who knows what methods required for meeting drawineg reqirements.

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No, a true position controls location/oriemtation. A profile form can control both location, orientation, size and shape. Making a lot of other tolerances un-necessary. Like size, roundness, location, etc.

[[SH...]]

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[[To...]]

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If not having curves or free form, could it be a possibility to use space points and evaluate them as profile form?

I am a fan of profile my self.
Unfortunately I think that a lot of people in construction are making profile tolerances too tight because they don't understand the profile.

[[Er...]]

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Thats my point, a profile tolerance can replace many other "call outs", thus making inspection simpler. Take a look at ISO2768-2 as one example.

And can you elaborate what you are trying to say with your last sentence? We usually dont fail our inspections, so I have never had any customer complaints about that. And if We for some reason fail, we wont "ship" the parts, since we can't guarantee conformance. We also don't edit our reports to show anything but the reality... 🙄

If you agree to manufacture something, and in the deal inspection is incuded. Make sure you have the equipment you need, or stay away from it.
I remember when we tried a supplier in India, think the name was Ge**on. Nothing but trouble, the inspection people over there could not interpreted gd&t, they didnt have equipment accurate enough for the tolerances. All reports we recived said the parts where in tolerance. Then we counter measured, and pretty much everything was scrapped... If I recall correct, they even switched material on something (cheaper stuff ofcourse) , so they melted when they did a "burn test".
My point is, if you agree to manufacture, but dont have equipment for it, or software to inspect, whats to complain about? Your fault, your mess. Its not an viable argument against profile tolerances.

Space points seems to be one common way to do it. But you will be limited in terms of DoF etc. It can be solved, but it takes more elbow grease. I've had curve and free form since the first day, so I never given the work arounds much of a tought. Actually Im quite spoild here, I point, they pay 🤣


Sorry for spinning away from the original question. Do you also have a size tolerance on the holes?

[[Jo...]]

Design for manufacturing is not a function of whether or not to use profile or any other geometric characteristic, for that matter. It's designing things that can actually be manufactured.

As far as profile goes, it's a powerful tool but not the best for everything. First of all you can't modify it at MMC or LMC. That's the biggest drawback, in my opinion, for locating holes and slots. Second, you get the most location tolerance on what would otherwise be regular features of size when you are in the middle of the tolerance zone. As you approach MMB you lose tolerance and as you approach LMB you lose tolerance, as opposed to position on a hole at MMC where you gain tolerance as the hole gets bigger. Also with profile the size of the hole is limited to the location tolerance (unless you're using dynamic profile which is new in 2018). With position, the size of the hole is one thing, the location is another.

Profile works well for some things, not so well for others.

[[Ja...]]

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For these holes, there is only minimum diameter requirement. (basic dim is Ø1.306 and callout says Ø 1.300 min true diameter. P.S. not that it matters with my question but the bores are angled with respect to top surface datum -A-; that's why there is profile callout on the print instead of location callout)

[[SH...]]

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