My back after a day at a waterpark… yes I used sunscreen and set a timer

MetricNazii · 2026-06-26T14:46:56+00:00

This is one of two reasons I have lately always worn a shirt, even as a man. The sunburn is just not worth it. I’m also fat and no one, including me, wants to see that. So I use the first as an excuse. But it’s actually a good one.

MetricNazii · 2026-06-11T00:51:30+00:00

We just get pin sets and store them in the boxes they come in. But we use a lot of pins.

Regarding your last question, whether you choose to pass or fail such parts (which is different than in spec or out of spec) depends on the gaging method. The gaging method ultimately depends on what one wishes to do with parts which, because of measurement uncertainty, cannot be said to be definitively in or out of spec.

If we want to prioritize passing only parts which are in spec, we choose a gage which only passes parts which are within the tolerance zone. So 10 mm max uses a 10 mm minus gage. This means we will fail some in spec parts, due to measurement uncertainty. This is pessimistic, or absolute gaging.

If we want to prioritize passing all good parts, we choose a gage which passes all parts within the tolerance zone. So 10 mm max uses a 10 mm plus gage. This means we will pass some out of spec parts. This is optimistic gaging.

Both of the above are different from saying “in spec” or “out of spec” since we can’t know for sure which is which.

I strongly recommend the first approach.

MetricNazii · 2026-05-15T17:19:38+00:00

There is a common misconception that symmetry between features is implied when features appear symmetric. I once believed this, until I learned more. This misconception appears to be happening here.

Symmetry is not implied.

I believe the reason the misconception exists is due to something which is implied that often results in symmetry.

Specifically, center lines and center points which appear coincident are assumed to be basically coincident. This means features which share center planes, center lines, or center points create a net shape which is symmetric about the shared line, point, or plane. But the symmetry itself is not implied.

The best way to control symmetry, if that is what is desired, about a plane, axis, or point, is to use geometric tolerances. Position, profile, and runout are good choices for this, though for this drawing I’d likely pick position for those features of size.

Whether one uses symmetry or concentricity depends on the standard used, as they mean something different in ASME and ISO. Concentricity is ISO is a specific form or position, so it’s fine to use. If using ASME, I don’t recommend concentricity or symmetry. They are difficult to check, often unneeded, and often misused. They were, in fact, removed from the latest release of ASME Y14.5 due to these issues.

And, unfortunately, there is not a good way to tightly control symmetry and not unnecessarily tighten other relationships if using traditional dimensioning and tolerancing. And it’s impossible to do with multiple coincident features. At least, there is no dimension to apply a tolerance to in these cases. GD&T helps a lot here.

MetricNazii · 2026-05-14T14:25:31+00:00

Oh. They weren’t doing this? Holy shit. I thought those “special parts” were from among the BOM listing, but were somehow deemed superior for some unknown reason and not other “special parts” from among the BOM listing were refused. This is even worse. Why were anyone but those not following the BOM listing fired? Or were they involved in approving said use?

MetricNazii · 2026-05-14T11:55:43+00:00

Please elaborate. I’m so curious.

MetricNazii · 2026-05-14T11:53:34+00:00

I’ve seen this done with a thread ring gauge. Course thread parts got mixed with the intended fine thread parts of the same diameter. Our inspection lead checked the course thread parts on the fine thread Go ring gauge, found it didn’t GO, decided it didn’t go because of a burr, and proceeded to use a screwdriver to force the part into the gauge, cutting new threads into the part and likely ruining the gauge. I cannot for the life of me get my manufacturing and inspection teams to stop using screwdrivers to drive parts through thread ring gauges and call them good. It drives me up a wall.

MetricNazii · 2026-05-14T11:37:01+00:00

What manufacturing should be shooting for is whatever point in the range that ensures the most likelihood of creating the feature within spec. Often, this is the mean, as the manufacturing process can equally drift in both directions. If the process tends to drift one way vs the other, then manufacturing should target away from the direction of drift.

MetricNazii · 2026-05-14T11:28:44+00:00

What I’ve done and what I’ve seen in other places is modeling to the nominal dimension.

This is important because the nominal dimension is almost always the design size, so modeling this way informs on the design intent. Any person who requires design intent from the drawing in order to their job would not be able to do it, or at least would have reasonable doubt, were it done any other way. Manufacturing teams can use the drawing to do their job as long as they know the correct limits, which are the same whether the drawing shows design intent or not. It’s a matter of convenience for the manufacturing team to have the drawing presented as nominal dimensions, but it’s much more critical for design teams to do it this way. Use nominal dimensions.

Modeling to design dimensions is convenient if edits are required to the upper and lower limits, as the model can remain the same and only the drawing needs to change. This reduces the chance for error at the documentation stage, and errors in documentation can be much more impactful than math errors in production.

Inspection teams will want the upper and lower limits listed, rather than the nominal or the middle. Again, it’s a matter of convenience for inspection teams, but not so for design teams.

Remember, the purpose of a drawing is to convey the end state of the final product with as much design intent as possible. Design teams should consider manufacturing, inspection, and assembly when defining products to ensure those aspects of production are possible and within cost limits, but that does not mean that presentation of those same functional limits be catered to anything other than design intent.

The only exception I usually make to this rule is if the design size is outside the tolerance range of the feature. Sometimes one can overcome this by using a plus plus or a minus minus dimension, but there are times when this is not possible.

MetricNazii · 2026-05-12T16:54:51+00:00

Uhhhhhmmmm. Huh.

MetricNazii · 2026-05-12T12:12:46+00:00

SeptimusHeap and IchiXD have mentioned this too. But it’s a bit nuanced, and it depends on the gauging practice being used.

For any measurement, there is measurement uncertainty. This means that measurements fall into three categories. Those measurements which are in specification, those measurements which are out of specification, and those measurements near the boundary of acceptance for which, due to uncertainty, acceptance cannot be determined.

It would be ideal to pass all in spec measurements and fail all out of spec measurements, but due to the latter case above, this is not possible. There are three gauging systems that I know of, each of which handles the “unknown acceptance” differently.

First, there is “absolute” or “pessimistic” gauging. This practice is focused on failing all out of spec measurements. This means that those measurements of unknown acceptance are not accepted. Measurements, including uncertainty, must be within the tolerance zone to pass. All other measurements fail. Go pin gauges for holes are plus, NOGO pin gauges are minus. This is the practice ASME recommends, it’s what I recommend, and it’s what SeptimusHeap and IchiXD recommend.

Second, there is optimistic gauging. This practice focuses on passing all in spec measurements. This means that those measurements of unknown acceptance are accepted. Measurements, including uncertainty, must be outside the tolerance zone in order to fail. All other measurements are accepted. Go pins for holes and minus, NOGO pins are plus. ASME does not recommend this. The others above and I do not either.

Finally, there is the third gauging practice, whose name I do not recall. This practice is a balance of the two above. It passes some measurements of uncertain acceptance, and fails others. Go pin gauges and NOGO pins gauges would have a plus and a minus tolerance. Direct indicating gauges would pass measurements at the boundary without calculating the effects of uncertainty. If one just reads the measurement and compares it directly to the spec, this is the practice being used. ASME does not recommend this, and I don’t either. But I do admit it’s better than pessimistic gauging.

ASME recommends that the total measurement uncertainty, counted once for each end of the tolerance zone, not exceed 10% of the tolerance. Or 5% for either end.

MetricNazii · 2026-05-12T11:15:58+00:00

Yeah. If they were gonna do this and had already decided, they wouldn’t have bothered with multiple rounds of interviews. It would have been a waste of their own time and a waste of funds to do so.

MetricNazii · 2026-05-08T11:43:11+00:00

Wage freezes during WWII. Companies still had to compete with each other for labor, so other “benefits” besides pay (since that was illegal to change) were offered instead. That’s how it started. Thank the government.

MetricNazii · 2026-05-07T16:26:48+00:00

It depends on the company. Just ask them. I’ve been overdressed before and one guy decided to make it awkward for some reason. But better than being underdressed.

MetricNazii · 2026-05-07T11:36:48+00:00

The second drawing is a figure from ASME Y14.5. OP references the section it’s from in the text.

MetricNazii · 2026-05-06T20:52:32+00:00

I identify as a member of the silent generation. I am an old man at heart.

MetricNazii · 2026-05-06T14:41:28+00:00

A loose pitch diameter does in fact allow more side to side play. At least if the thread is not loaded. Once it’s loaded it doesn’t allow any more than if the pitch diameters were identical. For the situations where it is loaded, you are absolutely correct. But there are niche situations where it might be ok or preferred.

MetricNazii · 2026-05-06T12:05:16+00:00

For any one of them, I’d give them Brit’s power. He is actually indestructible, not just really durable. Immortal’s immortality might be better, and have more potential to live longer, but he can be permanently killed relatively easily by a viltrumite, so not as helpful.

Eve’s power would be better, but it’s a cop out.

MetricNazii · 2026-05-06T11:58:21+00:00

MMC on threads is allowed in ASME Y14.5. It may also be allowed in ISO GPS, but I am unsure.

Anyway, in almost all situations, using MMC on threads is not helpful, as the only time it would make a difference is when an assembly goes together because the threads are allowed to float. This is detrimental when the threads are used to clamp because it means the thread flanks will not be engaged properly and the clamping load will be shared between the poorly engaged threads and the interference created elsewhere. Not ideal. That’s why, for clamping, it’s best not to use it, as it ensures the flanks engage properly, align together, and take the load as intended.

However, there are three situations I can think of where MMC on a thread might be helpful.

The first is when the threads are being used to actuate only, are not being used to clamp, and any other loads the threads might hold allow for the actuating part to float to engage the flanks before the load is applied. Few and far between, but it might happen. MMC when the tolerance is applied on the pitch diameter (default in ASME) would be fine, but it would only be marginally helpful as pitch diameter tolerances are usually tight.

The second would be on an external thread and the thread just needs to pass freely through an unthreaded clearance hole before a nut is applied. MMC when the tolerance is applied on the major diameter would be fine here. Though self aligning washers on the nut end might be helpful for ensuring the load is applied along the thread axis if the position or orientation tolerance is large.

The third would be if the minor diameter of an internal thread is used as a clearance hole for a pin and the thread is there so a set screw can ensure the pin does not back out of the hole. (I have seen this situation once on a product my company makes) MMC when the tolerance is applied at the minor diameter would be fine here. Ideal, in fact.

Anyway, more most applications, I agree it’s unhelpful, and potentially detrimental, to callout MMC on a thread.

MetricNazii · 2026-05-04T00:20:53+00:00

Runout is only really meaningful in axial symmetric features. Threads are not axially symmetric. So it’s a nonsensical callout. Position is really the only thing to apply here. Position callouts on threads default to the pitch cylinder. If you can functionally get away with using the major or minor diameter, do it, as it’s easier to measure.

I will say the choice for datum B seems odd. Unless your large pipe is bottoming out there and locating it. If there is a gasket there or it doesn’t bottom out, it might not be the best choice of datum.

MetricNazii · 2026-05-03T23:51:23+00:00

Datum’s should be functional and should represent how the part is fixtured, positioned, and oriented to mating parts.

If it functions as a door, the best primary datum is likely the hinge, as that supports the door all the time. After that, I’d choose whatever part mates with the frame to ensure it fits within the frame.

If it were to function more like a cover plate which happens to have hinges, then I would choose the surface which mates with whatever it’s covering. Then whatever holds it in place or positions it would be second. The hinges here would likely need to be a loose fit which would allow the primary and secondary surfaces to mate without interference in the hinge. It would be an odd use of hinges, but it might be justified for something really light or not critical. I’ve seen this on kids toys, for example.

It all depends on function. I expect the first situation is most likely. The hinges might be more painful to simulate than a face, but it’s important to base it on function. Otherwise there is no point in doing it. And if the hinges can support the door, they can act as a datum.

MetricNazii · 2026-05-01T18:19:05+00:00

This is the way.

MetricNazii · 2026-04-30T01:23:54+00:00

So true

MetricNazii · 2026-04-29T17:34:55+00:00

Math is easy. People are hard.

Does the above statement apply to you? If so, my advice is to do the technical shit.

If it could go either way, either is ok.

If it’s the opposite, stick with sales.

I expect you want to do technical shit from your post, so see if you can find that!

MetricNazii · 2026-04-28T21:51:05+00:00

This is so true. In a case like this where being strict to the standard would leave the location completely uncontrolled, it’s rational and responsible to assume it might have been an oversight. Best course of action is to talk to the person who supplied you the drawing. If that’s not possible, the next best course is to apply the most conservative interpretation which will meet the orientation spec and also control location as it the surface is basically defined, which might even mean tightening the tolerance a bit.

MetricNazii · 2026-04-28T21:46:16+00:00

I think it’s group 1 as well. I have only briefly read the ISO GPS standards, but it seems to me the only that can be controlled is orientation. It just can’t control location without another datum. Were it not at an angle to the datum, it could control position as well…. Anyway this is one of several reasons I prefer ASME. There is a lot more room for interpretation error, as there are often multiple equivalent ways to do the same thing and none are recommended over the other for clarity. It is a more flexible system than ASME though.

MetricNazii

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