r/Metrology

Hi everyone,

Edit: I’ve used an LLM to create this text. I’ve checked it and, if needed, made corrections. Hopefully you don’t mind.

I’m a engineer working at a machine-building company. We regularly use total runout on our drawings, depending on the functional requirement of the part.

Our metrology department is asking us to stop using total runout and instead split the requirement into separate form/orientation tolerances.

The main feedback we’re getting is that:

Total runout cannot be measured properly on a Mitutoyo CMM, and

It is even more difficult/impractical to measure manually.

I’m not completely convinced by this, so I’d like to hear some opinions from people who work with CMMs and GD&T every day.

My understanding is that total runout is specifically intended to control the entire surface relative to a datum axis, and that it can be evaluated on a CMM if the datum reference, sampling strategy and evaluation method are set up correctly.

I’m also aware that manual inspection with an indicator and a rotating spindle/fixture can be a very appropriate way of checking runout on rotational parts.

What I’m particularly interested in is:

Can modern Mitutoyo CMM software properly evaluate total radial/axial runout according to ISO 1101 / ASME Y14.5?

Are there situations where a CMM is genuinely a poor choice for measuring total runout?

How do you normally inspect total runout in your shop?
Would you replace total runout with separate cylindricity, roundness, perpendicularity, position, etc. requirements purely because of inspection difficulties?

If you do replace it, how do you make sure the resulting tolerances are functionally equivalent to the original total-runout requirement?

Are there particular measurement strategies or CMM evaluation methods that make total runout more reliable?
For context, we’re talking about conventional machined rotational parts, not extremely exotic geometries.

I’d especially appreciate input from people who actually program/run Mitutoyo CMMs and from engineers who have to decide what goes on the drawing.

I’m trying to understand whether this is primarily a measurement capability problem, a CMM software/evaluation problem, or whether we’re actually using total runout in situations where another tolerance would be more appropriate.

Thanks!

What is your opinion of CMM rotary tables? What measurements do they enable? How does the software keep track of part while it is rotating?

I once had a horizontal rotary chuck on an optical CMM, but adjusting the runout of the chuck had to be performed manually on each part and it was a pain. Eventually I stopped using it.

Recently I've seen videos of CMMs measuring gears on rotary tables and it looks like it would speed things up, but my past experience makes me skeptical.

What's the difference between that and just paying a standard calibration company?

When you draw a feature control frame for position of a hole, the primary datum should be a plane perpendicular to the axis of the hole. True or false?

https://preview.redd.it/g58oxtotskjh1.png?width=395&format=png&auto=webp&s=f1a145ed300c679b1fcf917a7f405baa134b931c

I'm reading Geometric Dimensioning and Tolerancing by David Madsen. I believe this book was published in 1995, so it's a little dated. But it says in the positioning chapter "The true position centerline is perpendicular to the primary datum."

R. Dean Odell also says as much in his position video. Time stamp 21:10

https://youtu.be/XbTbYxdrRYg?t=1270

I've got a part like this. And I feel like that hole on the left should have its own datum along its respective plane to serve as the primary datum in the FCF. Is that dumb?

https://preview.redd.it/ue9fr4kuskjh1.png?width=722&format=png&auto=webp&s=bd23eddb66e267236ddfac7ff00d62b0363a4c7c

This got me wondering how necessary perpendicularity of the primary datum is. So I set up the Zone3 training part on a CMM and on purpose I measured the left side first. This was not the face that the hole is born into. I'm kind of following the second example in my first image. So I measured 3 planes, and I measured the hole as a cylinder. I think it's also worth noting that I'm not using datum simulators, I'm touching off the part itself and I'm using reference geometry.

And it didn't seem to matter what order I fed the datums into the evaluation, I got the same calculation. If the axis of the hole is not true to the primary datum, I would expect an extreme failure. So what gives? Does the fact that I'm using reference geometry somehow override the logic of the datum precedence?

Thanks.

I’m learning PCDMIS now and I have two questions

1. Who the hell made this software?

2. What is the value in using Command Mode over Summary Mode? Seems like Summary Mode breaks down the whole program in a much simpler way. Any advise on how to understand command mode?

I'm 31 and currently work in software QA, with around 6 years experience and a Computer Science degree. I'm seriously considering switching into metrology/CMM programming because I'd like a more hands-on, technical career rather than being 100% desk-based.

I've started learning GD&T, coordinate systems etc. and have been looking into CMM programming tutorials (PC-DMIS/ZEISS Calypso) and I genuinely find it interesting and think the role would be a good fit for me.

For those working in metrology/CMM, how do you find it as a career?

I'm particularly interested in:

• What is the day-to-day work actually like?
• How stressful is the production environment?
• How good is job security/job mobility in the UK?
• Would you recommend it as a long-term career?

I'm attracted to it because it seems like a specialist, hands-on skill that's relatively resistant to AI/automation, but I don't want to romanticise it. I'm currently weighing it against staying in software QA, so I'd really appreciate honest opinions**.**

Thanks!

Does anybody have any experience incorporating a UPS battery backup onto a CMM? If we get power drops or surges it can tend to take our machines down for a bit while we power cycle. I'm not looking to run the machines for any length of time, but I would like enough runtime to park and shutdown the machine for extended outages. Most of the time if we have a power issue it's a flicker/drop for a few seconds. I tried contacting our CMM manufacturer but they weren't much help.

How do I calibrate my probe at an A90 B0 angle. I’m using Man+DCC and when I touch my probe at the top of the sphere and it touches the 3-4 points after about the that on about the 5th point it comes to touch it on the backside and obviously crashes. Obviously I’m skipping some steps can someone walk me thru step by step on how I can calibrate my probe please. Thanks in advance 🫡

(Indianapolis/Columbus IN Area/Remote) Guys and Gals. Ive been in QC/QA for a few years and running Calypso for the CMM. Recently I had an opportunity to move to a new company to attempt to fill an immediate need they have running PC-DMIS on a CMM they use once every 3 months, maybe. They are going to send me to the week-long class as soon as I can prep and get away. Yes, I know Hex and others can come but those take time to organize on my end.

They said, "Take a month, fire up the CMM, dive into the programming and see what you can learn on your own and tell us what you need" (don't trash them, they are fighting to get out of a mess with me). They've given me a part to learn and Ive taken 3 weeks and have a good handle. Ive read every help page, tutorial and video on Hex, XYZ, etc, You name it, ive looked or watched it.

I think I have learned quite a bit but I have nothing to compare it to and there are so many features built into PC-DMIS that it will take time to learn them all. I have a part that has 3 Datum and 10 total features to measure. I can set my camera up over my shoulder if needed and you can walk me thru some of these features I need to know before I finalize my program. Who knows, you may look at it and realize I know NOTHING and this is a lost cause.

Let me know what you think of this idea, i may be way out of line, just don't be a jerk, that's all I ask. Thanks in advance, Rich

Hello, I'm a beginner Metrologist researching the best tools for measuring Teflon parts. But, I cannot find any consistent resources stating why one tool is preferred over the other.

I know thermal expansion is a critical flaw of Teflon so I'm trying to find something to help resolve this persistent issue.

Questions:

Is it as simple as an acclimating in QC and measuring it with the same temp tools?

Does it need a consistent 3 point set-up on a cmm?

Is there a standard for an acclimation period?

Are thicker tools not recommended because they're more likely to transfer heat?

Any kind of knowledge or advice would help a lot!

Can anyone recommend their software of choice for inspection data analytics?

Excel does the job but my datasets are getting large and having a half dozen macros to calculate my histograms, control charts etc has me curious on what else is out there.

Im thinking MiniTab, Octave or even just Python. Anything that can handle large 500+ datasets and provide good statistical insights.

Bonus points if the tool has a good visual dashboard for the manufacturing floor or built in importing tools for Csv/cmm data.

Thanks!

Hi all, just stumbled on this sub and hoping someone could offer some advice or point me in the right direction.

I've been a CMM programmer for just over 2 years. I got this role as a sideways move from being a toolmaker, with zero prior experience.

I really enjoy the role and the sort of work we do, but I want to learn more and gain more experience but I don't know how. I programme on Metrolog X4 and have seen PC-DMIS through the Metrolog software but never programmed it myself.

Are there any courses or anything you can do as an individual in the UK related to metrology and inspection? My company will not pay for training. We've only recently started looking at GD&T so my understanding of this is really limited but I think it's an important skill I should learn.

Any advice for ways I can gain new skills or experience? Happy to self fund. I would just like to open myself up for more opportunities at other companies.

Thanks!