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I'd like to throw in my two cents in the hope that someone reads it and offers a counter opinion. I asked this same question in the GD&T Basics Inspection course and I agree that in an ideal world, anytime the UAME or local size reports out of tolerance, then the part should be rejected. But in my (limited) CMM experience, the UAME and local size rarely report within tolerance on a CMM when dealing with a tolerance that tight unless you have an analog scanning probe or take an extremely dense number of hits. And I'm talking like a point every couple of millimeters (who has time for that?). And even then, it can sometimes report slightly out of tolerance. I'm sure it has something to do with the math involved, which is beyond my knowledge. I've come across this more times than I can count when measuring drill holes for example where the UAME reports too small, yet the plug gauge always fits. But we don't have functional gauges for every single feature that we machine. Sure we have bore gauges and micrometers, but those just give a two point dimension. So I have no other choice but to rely on the average size (or least squares in CMM terms). It's also a lot more repeatable. Do I like it? No, I hate it. But realistically, if I were to fail every part where the UAME or the local size reports out of tolerance on the CMM, then I'd be rejecting about 80% of the parts that we make. And that doesn't help me, the company, or the customer. Again, I want to stress that I get much better results with an analog scanning probe vs taking hit points, but even that has its limits and not everyone has one of those. That also comes with other things that need to be taken into consideration, like using the correct filter for instance. But that's another topic entirely. So in my view, when dealing with tolerances as tight as the one in the video, the average size is often a necessary evil when the UAME or the local size reports out of tolerance. If anyone else experiences the same thing or has a different view entirely, please chime in because I'm still relatively new myself.

I put GD&T on my drawings to better define my parts and give the machinists more tolerance. But the parts are always quoted more expensive because they have to have more experienced technicians interpret my drawing and they say it requires a CMM inspection now. How would you respond to this?

Thanks, How to define tolerances for different surfaces on part? For example we have Bumper and we want to define tolerances on this part on different points (X,Y,Z) How we calculate? ❤❤❤❤❤❤❤❤

I'm designing components for high volume manufacturing (>100,000 pcs/y), so we have to rely on process capability for quality assurance. What are your thoughts on the use of MMC/MMB or envelope, in combination with process capability? Is it feasible or not?

its larger the hole smaller the material condition .

Excellent explanation

I've learned more from these videos than what I learned from college. Thank you!

(1:52) Can you use the MMC modifier and still ensure a minimum wall thickness? Yes, you can by reducing the Position Tolerance = $$!!.

So it means, I will add bonus tolerance to position tolerance(0.05 mm) , after datum B and and C size measuring. For example if datum B size is 25 mm I will add 0.05 mm. If datum C size is 30 mm, I will add 0.1 mm. I measure feature itself as 10 mm, I will add 0.1 mm. In final condition it has 0.05 + 0.05 + 0.1 + 0.1 = 0.3 mm position tolerance. Is it correct?

This is such a helpful video. I refer to it regularly! Thank you for posting it.

Can we use one of the axis of the hole as priamry datum, and apply parallelism to the other axis of the hole respect to the primary datum? If yes, only primary datum wouldn't be enough to control all six freedom, how should we pick the secondary datum or even a tertiary datum needed?

Very Good video on explaining Profile Tolerance. I enjoyed the clear and informative content; nothing extra; straight to the point.

1) I‘m afraid, there is no reale feature function according to „flatness 0.005 M“ at datum A. 2) If this plate is srewed or stacked, a complete differend specification is required (please see: The plate can be screwed from two different sides). 2) If someone wants to use „flatness 0.005 M“ for whatever reason, then it is easier to write 1.000 -0.02 +0.025 without additional flatness. Kepp it simple! If a fit is required, it‘s a very good idea to keep in mind the gauge, which explanes the simulation of the missing contact partner. If you work with 3D-CAD it’s very helpful to work with assembly constrains to explane contacts. If you create a nominal design where all features with fit function are at MMS, all parts in your assembly are representing the go gauge against each other! A specification is only necessary to control maximum of fit clearance. Unfortunately with the modell of GD&T (or IS0 GPS) a specification uncertainty against nature function appears. Should we start to speak about this issue?

I’ll save some people time. This is not a software tutorial for programming a CMM. It’s only using a CMM for measurements.

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Yes, it is obvious that when a datum plane is define by 3 datum target points, flatness is meaningless because they will always form a perfect plane. however, when the datum targets are surfaces instead, with meaningful areas, or you have more than 3 datum target points, you will have a flatness mismatch between a simulator and the real part. Is there a way to impose a restriction to the deviation of those multiple points or surfaces from a perfect plane, without qualifying the entire surface? (for example, you have four contact points, and you want to make sure that with any 3 points in contact, the fourth point will never have a larger gap than a certain value)

If datum targets are applied, how to simulate datums during inspection via CMM. Should fixture must be used? Is there any option by CMM software or programing?

Thanks

Very well explained!

a Vivid video presentation👍

Thanks a lot. very useful training. god bless you.

May be datums B and C are equal: A | (B-C) MMC

The 8 holes would need to be a simultaneous requirement output per ASME 14.5 right? Would software treat them more as a single pattern instead of separate features if output as a SIM. REQT.? Would the results really be any different?

You didn’t talk about the modifier. How can you have a MMC without a tolerance of size?

Thanks a lot!

Hey thanks for this explanation! Question 8:23: Is there a difference for the manufactured part to inspect if you: 1) Have Datum A on the surface (like in the video), or if you put: 2) Datum A onto the flatness callout itself, and not on the surface? Does it matter or is it actually the same? Thanks :)

So professional! not only about the GD&T, but also about the thread measurement

What is repeatable measurement

Is there a way to determine the direction of the probe such that the surface is normal to the direction of the probe at point of contact?

Perfect, thank you.

I finally have a reason to use my salad bowl.

Wondering as you the delete datum "C", at 3:20, can we delete datum "B" from the 2nd line of control frame of Example 2 (for tol. 0.1)? To allow rotation but with in the area for tol. 0.5 ?

As far as I know, the material conditions might be applied only on feature of size. What should be the MMC value of a point, which is an intersectoin of five axes? Are you going to add the MMC of every cylinder? I think - no. Are you going to find the MAX MMC of some cylinder an use it? Or is it the MIN value? Think it is not correct either. Also, cannot think of any real world problem, that will require such dimensioning schema. Of course, if it is going to be a check gauge - then, yes, it might work. But, don't think the CMM will be able to evaluate this.

Thank you so much.

Thank you for answering my questions. This video is clear. Now I am more confident to discuss with my colleagues. Super appreciated.👍👍👍

Very interesting video. 2 questions here, which I think were not clear: 1. While in the nominal case, those 5 cylinders converge to a point, in reality they will not. The axes will kind of miss each other in 3D space so how could a single point be determined? 2. Regarding the orientation in plane (that fixes the rotation of the pattern of 4 holes), you mentioned that you can choose whatever you want. But again, since on the actual part, those 5 cylinders will not have the nominal angles, is the reference orientation considered as an average between the orientation of those 5 cylinders? Otherwise, choosing just one would imply that it is a difference to which one you choose, since the will have different deviations to the orientation. Thank you very much!

I started at SDSU 8 years ago now as an ME and never heard about this until now. Gd&T was just briefly mentioned in my cad class and that was it.

Air gage, what is that? Not ever heard about that.

Using the hole positions as Datum B does bother me. It feels to me that this part will ride on a shaft, and it's most important to ensure the parts features are centered on the shaft. Therefore I'd prefer to see the ID 1.000 +/- .001 to be Datum B. Subsequently the bolt circle diameter and hole positions would be slaved to the bore. Trying to measure the position of the 1.500" boss based on the position of holes that themselves may have up to .0025" deviation seems ambiguous.

Why do people ask these obvious questions? You want to know the cylintricity, you MEASURE CYLINDRICITY. You can't just measure something else and then just assume things. That is the first step to bad engineering, where components end up being functional by chance or overengineering, not by virtue of good design and control.

Thanks!

This is very informative thank you. 👏

A point can't be a secondari datum I don't see it over restir same F.D. more Tham ones it error

Hi as a teacher of Mechanical Engineering, I find your videos a great resource and encourage my students to watch them. Thanks

At 9:58, shouldn't the original point(Zero) be the intersection point between datum A and datumC. What you want to express is that we can add X value depends on the Pin the inspector will be choose, is that correct?

abseloutly amazing

Your video mentions a polar probe or a TIR checker. It'd be cool if you included slightly more details on those types of tests to educate people. Searching either of those didn't come up with a ton of useful links. I assume we're talking about a system that checks with multiple sensors to monitor for the lift of the center axis such as czcams.com/video/fIbt7lBTL2s/video.html or a CMM setup that can plot the polar graph (either cause the part can lay flat normal to it's rotation axis or you have the part between centers or some other method.

I ask this question to geotol pro if I can use runout as datum and the answer is no. Runout should be reference to axis. And runout callout cannot be attach to dimension. Conclusion. They should overhaul gd&t.

The inclusion of runout callout for datum A and B, with a diameter tolerance of 1.5 +.000 -.002, is unnecessary since the size tolerance is smaller than the runout tolerance. This incorrect example contributes to confusion among beginners and diminishes the widespread use of GD&T.

What would be the difference if you used a composite position tolerance, instead of a multiple single segment? And is there an equivalent to composite tolerance in GPS? Thanks!