r/Metrology

We had a part arrive where it had been made to CAD and not the drawing. The CAD was different to the drawing. The supplier is stating CAD is master and we are saying drawing is. Is there anything I can point to that says which is master unless otherwise stated. The drawing does not say.

Hello all, im fairly new into this line of work(about 3 ish years) and i was just curious what people get paid in metrology(if you are comfortable sharing). I just bounced to my second shop and have been thinking about where my ceiling is. I've got a pretty good handle on the basic GD&T, understanding of the 6 degrees of freedom, a damn good handle on Calpyso, and a new start into MCOSMOS.

I just wanted to see what other people around the world are doing in metrology, along with the knowledge and money that comes with it!

https://preview.redd.it/k69jxfa62qzg1.png?width=1275&format=png&auto=webp&s=1c756b3ed92ebb2bcf57ddae38c4d8be8e39661e

I know there is little benefit to applying MMC to threaded features directly. However, consider the case where a pattern of threaded holes is used as the secondary datum feature [B] with the plane in which they are located as the primary datum feature [A].

When evaluating other features on the part (Ø21 hole position tolerance or profile tolerance in the example drawing), I'd like the datum reference frame to be [A | B(M)] so that I can use a portion of the datum shift available from the mating part's Ø14 clearance holes in the part alignment.

https://preview.redd.it/dvckyw4iwmzg1.png?width=922&format=png&auto=webp&s=ad11e97dc2aa58ceea02111c992f51c669cacd31

https://preview.redd.it/491rdx8aymzg1.png?width=358&format=png&auto=webp&s=3d1c2fe27ff774f43f2e638ba0add19fac641ab7

Now, the calculation for available datum shift due to MMB modifier on the datum B feature reference is dependent on the size tolerance of the feature (irrelevant/difficult to measure for thread pitch diameter) combined with the position tolerance of the datum B features with respect to Datum A and the other features in the pattern. Refer to ASME Y14.5-2018 Paragraph 7.11.5/6 and Figure 7-22 for MMB calculation.

From 7.11.5 "The appropriate boundary is determined by the collective effects of size and any applicable geometric tolerances relative to any higher-precedence datums."

If the pattern of threaded holes (datum feature B) has a FCF of [POS | Ø2(M) | A], then the "true geometric counterpart" of datum feature B at MMB should allow an additional Ø2 of clearance. Meaning a M10 threaded hole has a Ø2 undersize true geometric counterpart.

Perhaps this is easiest to apply if we specify Datum Feature [B] as the "MINOR DIAMETER" of the threaded holes (or "MAJOR DIAMETER" for male threads). Then, in this example, we can use a pin Ø2 undersize of the drill size (8.5+/-0.1mm) that creates the minor diameter.

Have any of you used MMB on threaded datum features? Does metrology software support this case?

Are the hexagon classes worth it?

I am a mechanical engineer thrust into quality to help relieve some pressure. We have a fowler (aberlink) cmm.
We are being asked to measure some small gear teeth to a .02mm profile.
I do not think we have the right tools for the job, I could be wrong. But looking at vision systems, I am not even sure they are the right tool. Just looking for input from real quality personnel. If you tell me that tolerance is wild that is good information too!

Edit: It is a type of hirth coupling not a traditional gear (thanks to u/involutes)

Hello,

I ran across this website and products yesterday

https://www.trueprecisioncorp.com/

Is anyone actually using something like this to measure pitch diameter of threads? It looks like they have been around for a while but im suspicious that no one bothers to do that work.

I've heard the debate of measuring threaded holes with a single straight gage pin and ignoring mmc. the size of holes im talking about are 2-56 thru 3/8-16

Hoping you folks that actually work in metrology can weigh in on how you are actually measuring true position of threaded holes RFS or at MMC. I still think calling them out at MMC is silly but maybe its compelling if folks are actually calculating bonus.

Calling all Calypso 3D scan measurement experts - please help!

I'm currently tasked with a rather large project rescanning and measuring airfoils. Each airfoil has a measurement regime across three airfoil sections and all of the measurements are working except for one. I did not do the initial programming in Calypso and although I am my companies SME for scanning we don't normally use this software at all so I'm struggling to find where the issue is.

I have performed these measurements on two different airfoils to ensure that it wasn't a scan/STL issue and it happens on both. I have also checked the program vs the two other section programs and other then nominal values variation everything seems to have the same basic setup so I'm unsure where to go from here.

What I've Checked:

• Alignment
• Clearance Planes
• Characteristics Nominal Values and Tolerances
• Features - Feel like my issue is here but don't know where to start but only 4 out of 13 features programmed are green boxed on left

Any suggestions at all for anything else to check would be appreciated.

Hi everyone ,

while programming a part yesterday on Pc-dmis i found a dimension of 25+0.1/+0.05 , i never saw this type of tolerance and i dont know how to interpret it , i tried to search online but i dont found any informations about it , so the thing that i want to know is what is nominal and tolerances that i should add and how to calculate it and if anybody had a documents or resources please share it with me and thank you in advance .

I have this need to measure coordinates of different features of large-ish machinery (up to like 10m high), and I would like a system I can set up on site, do my measurements, and pack it up with relative ease. I would be acceptable to stick some markers on the target while on site, but the setup and teardown can't take hours.

I also do not need high precision, ~1cm would be more than enough. I am aware of tracking systems like Leica laser-based, Creaform, Keyence WM, and OptiTrack, but they all seem overkill for what i need. The budget would probably top out at 30k$, but ideally it would be more affordable, since I don't need high accuracy.

Does anyone have recommendations for metrology systems that would fit this use case?

Hi yall, i was thinking about making some kind of a group with other calypso users/programmers/etc, are there many of us? Maybe im a bit too interested in CMM but i love it, its kinda as if my job was my hobby as well. If it wasnt so expensive id totally buy at least one machine and make my own measuring company. So yea, anyone interested, hyped or just curious as i am?

I'm finding conflicting info online depending on where I look and wanted a straight answer. Some sources say the pitch or effective diameter is a function of the major and minor diameter at the midpoint, some say it is a direct measurement of P/2, which can also be found by measuring the fundamental triangle of the crest and root and getting the midpoint of those.​

Is my understanding right that pitch diameter is only reliant on the form of the thread and the major diameter does not factor in at all? Measuring with pitch micrometers on a truncated crest thread and getting differing ​results. Thanks.

Just started a new job and they have a portable rotary table that needs to be used for a few parts. I have never set one of these up before, there are no work instructions and the previous programmer has been gone for a month.

I’ve tried looking through the forum for setup/qualification instructions but haven’t found a step-by-step process. Can anyone provide some info or point me in the right direction?