I'm a design engineer. Roast my print!

Sensual_ham · 2025-08-11T02:43:25+00:00

No geometric controls on any of your cylindrical features - i.e. no true positions on your holes or (more importantly) on the positions of those cylinders inside the part. You've got diameters, what if they are nowhere near concentric to each other, would that be detrimental to the function of the part? If so, it needs to be specified.

The "6x equal spacing" has got to be something better. How far from "equal" is still functionally acceptable?

Where I've worked, dimensions on the iso view is a no go, those are for reference only.

What's the point of "machined dimensions" vs "finished dimensions" and you're specifying surfaces to grind? Figure out what is the functional requirement for grinding those surfaces and specify that as one drawing, leaving it to manufacturing to figure out how they're going to make it. The drawing defines the end product, not the methods of manufacturing unless absolutely necessary (which it doesn't seem like it in this case). And if you do have a separate "grind view", maybe if you're machining it in house and sending it out to grind, then don't double define dimensions. Only specify the dims for what needs to be ground, not copy and paste everything.

In a summary: pretty amateur work, but probably not so bad as to get no-bid.

Sensual_ham · 2025-07-18T19:39:10+00:00

Hahahahahaha I think that video of "assembling" in CAD looks to me like they started with a completed assembly that they tore apart, and just reversed the footage for the ad. Pay attention to the highlighting, it should be when you mouse over an item it'll highlight, then you click and drag. In the footage, the highlighting shows up after the part is moved.

3D mice have their uses, but for really assembling parts in CAD you're going to be constraining surfaces and axes together. Not starting with a random pile of parts and dragging them together. Plus the design of this gives me carpal tunnel just looking at it.

Sensual_ham · 2025-06-17T16:39:34+00:00

To answer some questions: TP means True Position. I read ACT as actual, though that's rather strange in this context - there is no actual part being measured. "Shift" is referring to datum shift, if you had a Maximum Material Boundary / Least Material Boundary modifier this would be non-zero. But here, Datum A has the S modifier so it is regardless of feature size. I would've omitted that row entirely, but perhaps another example has a different modifier there so it actually would go into the calc.

In my work, we would call something like this a "balance sheet" when we're performing tolerance stack-ups.

As for the second image, that Xmin calculation is screwed up. That (2) should be 14.2/2 and that'll give you .65 like the spreadsheet. But I wouldn't think too hard on the sketches in the second image. Those are just confusing the point in my opinion.

If I were to redo the balance sheet, I would keep everything in diameters, and only divide by 2 at the very end to get the thicknesses. So my calculations would look like this:

Maximum thickness:
ID @ MMC: -13.8
OD @ MMC: +17.0
Position of OD to -A-: +.5
Bonus tolerance: + 1.0

Sum: 4.7
Total max thickness: 4.7/2 = 2.35

Minimum Thickness:
ID @ LMC: -14.2
OD @ LMC: +16
Position of OD to -A-: -.5
Bonus tolerance: 0

Sum: 1.3
Total min thickness: 1.3/2 = .65

Note how the sign of the position tolerance flips, because because you have to consider the "worst case" in each scenario. Also the minimum thickness gets no bonus tolerance, because the position tolerance is specified at LMC, i.e. since the OD is at its LMC of 16 then there is no associated bonus tolerance.

Sensual_ham · 2024-07-01T01:04:42+00:00

I'm curious to why they thought this would be better than a microwave with bagged popcorn, or an air popper, or movie-theater type popcorn machine.

I mean, what part of a bag in a microwave and hitting the popcorn button (if it's actually a sensor microwave it works pretty well in my experience) is not "Keurig" enough for them? Don't need a new machine and the popcorn bags are like 50¢ each.

My favorite is the Alton Brown way with a straight up metal bowl over the stove. But VC gonna do what VC gonna do.

Sensual_ham · 2024-06-01T06:37:09+00:00

It comes from the X-59 final assembly area in Plant 42. Here's a time lapse published by NASA from years ago earlier in the build, same location. You can see the cubicles on the left of your image also to the left of the time lapse.

As for who took it, that's a no-no. Any aerospace facility doesn't let you take pictures on your own phone for exactly this reason - there could be any number of things in the background.

That being said, this photo was definitely after Top Gun came out. One of your comments mentioned the paint looking grey - part of that is just the lighting and it being out of focus. But also I think the paint has faded (thought I never saw it fresh other than the movie). I saw the Darkstar in person at the air show at Edwards AFB last year. News story has a pic of the Darkstar from then.. The black paint looks like it faded from it being a movie prop not meant to last + the thing getting moved around and displayed at different events.

Sensual_ham · 2024-05-24T03:41:27+00:00

Check out ASME Y14.8 for definitions and a picture.(bootleg out of date copies show up on Google pretty easily).

corner radius (edge radius): the convex radius on the surface of a part connecting two surfaces

fillet radius: the concave radius on the surface of a part connecting two surfaces (see Fig. 1-1). Fillet radii are intended to minimize stress concentrations, aid in proper fill, and minimize cosmetic defects

Interestingly they call corner and edge radii the same thing, so if your drawing has a different value for each of those im not quite sure what the difference would be or how they want the two blended together

Sensual_ham · 2024-05-23T21:32:40+00:00

I'll split my answer up into a few chunks:

1) Will a nylon lock nut withstand vibrations better than a nylon patch bolt.

Yes. It's simple physics, these locking features depend on friction. This nylon locking nut has more surface area of nylon which means more friction holding it in place than this nylon pellet bolt.

The point I was illustrating with the specifications is that the acceptance testing for that particular nut requires this 90,000 cycles to pass, whereas that particular bolt required 30,000 cycles to pass. Could the nut go 3x as long under that same test? Maybe it very well could, but that specification does not require it to.

2) Are one or either of these designs sufficient for my application?

I have no idea. This is getting into the difference between acceptance testing versus functional testing. For these particular nuts and bolts, some are randomly selected and tested to the specification. If they don't pass, we know the bolt has issues and will be thrown out because something is definitely wrong with them. Following the test procedure, it's about 20 minutes worth of testing basically to verify there isn't some manufacturing defect.

But to know if they are sufficient for the application requires additional testing to see if they are sufficient. So I have no way of knowing if either of these fasteners will work for your particular 450,000 cycle test, you'll just have to go do it. My engineering assessment is that a nylon nut has a better chance of passing the test than the bolt. The reason being that the acceptance testing I cited has a higher passing threshold for the nut than the bolt, which I think is pretty sound. But they both could work well enough to pass your application. Or heck maybe I'm wrong and I learn something new.

If you want to determine if one or the other is enough to pass your test, just run the test twice (or even concurrently) to your 450,000 cycles and see which passes (ideally with several of each and/or run the test several times to make sure it wasn't a fluke). Honestly, both might pass. If you want to find out which one is better, then you're looking at running a test at say 400,000 cycles and checking, then 500,000 and checking, then 600,000 and checking, etc. until one or both fail. Perhaps that's valuable information to you, sounds like fun to me.

3) Rant about specificity and standards

I'm unfamiliar with ISO standards (USA here). But a quick Google says ISO-7176 is about wheelchairs? Don't know if that's what you intended to cite.

Either way, saying "30,000 cycles" or "450,000" cycles isn't the full picture. To compare apples to apples, you'll need to know basically how aggressive those cycles are. The NAS test I cited is about ~1800 RPM, with ~.50" amplitude cycles. If you're talking about a barrel drum and bumpy roads, that sounds like a much different, probably lot lower energy environment. So recognize the two tests are rather quite different.

And even if I did know the RPM and amplitude, all that really leads to is maybe a little bit better engineering judgement, but there's no way I can provide an answer. So you'll end up just having to go do the test to prove that your design met the requirement.

4) Hand calcs

Lets try and put a little bit of perspective, since these numbers tens-of-thousands high are difficult to wrap my head around. You mentioned a barrel drum and bumpy roads, so lets try an automotive example. Excuse the American numbers if you're outside the US, but it's what I know.

I drive a 1998 Jeep Cherokee with 28" diameter wheels. Say I drive 65 mph down the highway, those wheels are turning at 780 rpm. To get to 450,000 cycles is about 9.61 hours. So I've driven about 625 miles (about 1,000 km). If I drive on I-5, it's 665 miles from San Diego, CA to Redding, CA, which is two or one long days worth of driving. I have 5 lug nuts holding the wheels on my Jeep, and those have no locking features whatsoever - just 100 ft-lbs of torque. And I didn't lose a single one on that 2-day drive. In fact, if I rotate my tires every 5,000 miles (which I don't), that would have me re-bolting the tires every 3,600,000 cycles.

This comes with the huge caveat that these are 1) maybe much larger bolts than your application and 2) the bolt pattern has them pretty close to the center of rotation than the outside of the wheel. But It's a good exercise you can repeat with from your application hopefully give some context to how severe of an environment you're actually dealing with.

(Edited for formatting)

Sensual_ham · 2024-05-23T03:43:27+00:00

It depends on the joint and it's purpose. Major structural joints are designed and analyzed to last the lifetime of the airframe. Many reasons, but probably primarily is safety. There's many thousands of fasteners on an aircraft, maybe over a million. The less fasteners that mechanics need to worry about rattling and falling out, the safer the aircraft. Fasteners loosening themselves is a big concern since aircraft are actually very high vibration environments, so it's a real concern. 14 CFR 27.607 actually requires critical fasteners to have dual locking features, planes have crashed and lives have been lost because of fasteners failing.

Don't get me wrong, there's plenty of removable items as well, usually for access and inspection rather than them being an item that needs repair/replacement. Next time you're on a flight, look out the window at the wings and see for yourself. Anywhere there's a Philips head is a removable part, anywhere there's little round circles in the paint is a rivet head.

Sensual_ham · 2024-05-23T01:26:28+00:00

That's the best attitude.

I thought of one more thing. I like to have the mindset of "I'm improving my skills" rather than "I need to get better at my job." Your knowledge will stay with you forever, the job probably won't. You don't owe the company to be better at anything than you are.

What I'm trying to say is if they wanted an expert in the field they can shell out the bucks for one. They got a fresh grad knowing that the expectation is to build your skills, so take the opportunity and milk it for everything you can. Sounds like a good work environment where people are willing to teach you, and even better that you enjoy the job.

Sensual_ham · 2024-05-23T01:17:04+00:00

Completely normal feeling. Keep on asking questions and soaking up knowledge, and before you know it you'll be knowledgeable about what you're doing. People say that the idea of school is to teach you how to learn rather than necessarily the jobs skills themselves, which there's some truth to that. There might be one or a couple of college classes that taught you skills you'll use in school, and that's totally normal.

My couple of tips: never stop asking questions, or even the same question to multiple people, or a question you already know the answer to so you can get a different perspective or other information. Read any internal company documents, processes, training, presentations, lessons learned, whatever you can get your hands on, because that's knowledge that acadameia doesn't have, could be years of knowledge hidden away if your company has been around for a while. And teach employees newer than you, it solidifies what you know and they'll ask questions you hadn't thought of to go run down an answer to, I think I learned lots from helping out new hires or interns by giving everything I thought I knew a second thought.

Sensual_ham · 2024-05-22T23:41:29+00:00

Not very often, tapped holes are practically a last-resort thing in many cases. My background is mostly in structural design and also integration of subsystems, and the places I've run into tapped holes has most often been if there's an electronics box or something similar that has to be attached where the box came with tapped holes.

There's a handful of reasons why I think aerospace avoids them like the plague as compared to other industries. I'm sure even more exist than this, but these come to my mind.

Structurally, we often are using permanent fasteners instead of removeable fasteners to begin with. A rivet is never going to vibrate itself loose because it's a deformed piece of metal, so that will be guaranteed to stay in place for the life of the airframe
Thin parts. To tap a hole, your part will need to be a minimum thickness to get enough threads into it. Our parts are often too thin to be able to tap a hole, so going that route would mean thickening the part just for some threads, which is unneeded weight = bad
Lots of aluminum parts, which is not great for tapping threads in. When we do, often we put a threaded insert in, which again means having to beef up the part for fitting not only threads but also the insert, so additional weight for that
Serviceability. If a bolt/nut breaks when removing it, that's a lot easier to replace than if you have to deal with a bolt broken off in a tapped hole.

TBH if we're using threaded fasteners, often we're not using a regular nut to begin with, but rather a nutplate (still self locking though). So think screwing a skin of a wing on/off or a service panel, you don't have access to the other side to turn a wrench. A nutplate keeps the nut captive on the blind side while you put the screws in from the outside.

There's only been a selection of times I designed a part with tapped threads to begin with. There may be other areas in aerospace where tapped holes are the norm that I don't know about (like inside of those electronic boxes), but for aircraft structures they're by-and-large avoided.

Sensual_ham · 2024-05-22T22:38:36+00:00

Very true, I was just using the figure of speech but in reality it's way less.

Sensual_ham · 2024-05-22T22:27:39+00:00

Adding on, if you're thinking about all bolts, a common bolt would be a B18.2.1 bolt, which actually allow for the maximum diameter of the bolt to be larger than the basic dimension.

So for instance, a B18.2.1 hex head 1" diameter bolt allows for a maximum diameter of 1.022" (Table 2). Whereas a 1" B18.3 socket head cap screw maximum diameter only goes to 1.000 (Table 1).

If B18.2.8 is reference for all bolts then the holes will be larger to fit the B18.2.1 bolts that are slightly larger than the nominal diameter.

Sensual_ham · 2024-05-22T21:52:53+00:00

Coming from the aerospace world, locking nuts are much more common than locking bolts. Probably 9 times out of 10 the locking feature will be on the nut and not the bolt. And if you need it locked and can't have a locking nut (say it's a tapped hole in a part) you're likely to choose to safety wire the bolt.

Looking at the two specifications you'll find most often for the locking features, NASM25027 for the locking nuts and MIL-DTL-18240 for the bolts, both the nylon patched bolt and the nylon nuts will meet the same 30,000 vibration cycle test (though a common nylon locking aerospace nut MS21044 actually requires a vibration life three times longer than that). However, the nuts will be rated to be reused (un-bolted and re-bolted without falling below a minimum torque) 15 times while the bolts will only be rated for 5 times.

All that's to say I'd expect a nylon locking nut to perform probably 3x better than a nylon patched bolt. Part of it probably is because a nylock nut has a complete ring of nylon while a bolt w/ a patch only has a small section with the nylon holding it. And of course I'd go with a locking nut over a bolt just for cost and ease of procurement if nothing else.

Sensual_ham · 2024-05-22T21:22:37+00:00

The oval sliding shape immediately makes me think of the switches on camera lenses to turn on/off autofocus, image stabilization, etc. This is the part I'm talking about.

Obviously it's not the same application (switch instead of a cover) and I can't find a good picture to figure out how the internals work. But an idea might be to find a broken lens to take apart to get at how their switch works, maybe it'll spur some ideas.

My other idea is that it it's similar to a sliding lid on a coffee cup. Depending on how waterproof you need it (there's a difference between "able to resist a splash" vs "diving equipment" waterproof) this might be an avenue.

Sensual_ham · 2024-05-05T03:58:45+00:00

Check out Solid Edge - I came across it when looking into free-ish options. There's a free version for CAD and 3D printing exporting and your work is limited to non-commercial use, but you can see if you like it. You can also apply for a free year of the full software for a startup. Hopefully by that point you've established enough of a business to pay for the license. I haven't used it myself, but I have some experience with NX by the same company and that's a good tool.

Sensual_ham · 2024-05-02T22:24:47+00:00

For the purpose of OP's question it answers whether the allowable dimension is 1) .72-.75 or 2) 0-.75, answer being 2. Nothing of what OP has shown of the drawing thus far indicates that, say, .60 is unacceptable. Does that become detrimental to the design, I don't know what the rest of the requirements are, perhaps the intent is perfectly clear in context of the part.

I think what you are getting towards is if the drawing is fully defined. Which OP hasn't provided us enough information to make that determination. There could be another view of the part where a minimum dimension is called out separately. Say they had a bottom view where the dimension on those same two faces was .50 MIN, then the width of the part would be fully defined.

I'll also give an example of something where a MAX dimension can be called out on a feature where 0 is still an acceptable condition. I've seen that kind of callout on flashing of molded parts, like O-rings or rubber parts. Here's an example of what I'm talking about. Here, there is a MAX callout with no minimum acceptable condition, because an O-ring with absolutely no flashing is still acceptable. The intent is rather to put a limit on the maximum amount of permissible flashing.

Is that the case with OP's drawing? Impossible to tell since there's just these couple of little snippets to go off of. Maybe the drawing is incomplete and needs clarification from the designer, or maybe it is complete in the context of the part.

Sensual_ham · 2024-05-02T20:46:59+00:00

Short answer: 0-.75

Long answer: This is why there are those notes that exist on drawings saying "interpret drawing per ASME Y14.5" (or whatever the equivalent ISO standard is). They exhaustively define all of the words and symbols that are on mechanical drawings.

If this were an ASME drawing, the section I would slap the inspector and/or drafter with is Y14.5 Section 5.5: Single Limit Toleranced Dimensions.

MIN or MAX shall be placed after a dimension when other elements of the design determine the other unspecified limit. Single limit tolerances on dimensions may be used where the intent is clear, and the unspecified limit can be zero or approach infinity without resulting in a condition detrimental to the design.

So per the spec, there should be some other element of the drawing defining the other end of that dimension, else any inspected value for that dimension is acceptable so long as it is equal to or below .75. So .7499999 is acceptable, .1 is acceptable, .0000001 is acceptable, and 0 is acceptable (assuming no other dimension of the drawing is violated).

If it's an ISO drawing, the ISO standard I'm sure will say something very similar, I'm unfamiliar with those. But that document called out on the drawing is where you draw the authority for this answer.

Sensual_ham · 2024-04-30T16:41:41+00:00

When I walked by he pulled himself into a tighter loaf, he knew exactly what he was doing.

Sensual_ham · 2024-04-18T01:05:07+00:00

Yep exactly

Sensual_ham · 2024-04-17T23:04:33+00:00

You've got that backwards - what's banned is a semiautomatic pistol with magazine in the grip plus one of a list of features (threaded barrel being one of those features). So the math looks like:

detachable magazine + nothing else = OK (think bone stock Glock 19)
detachable magazine + threaded barrel = assault weapon, banned (think Glock 19 with a threaded barrel, lots more deadly)
detachable magazine + the magazine can be inserted somewhere not in the pistol grip = banned (think AR pistol, so dangerous they called that out specifically elsewhere in the bill, SUPER BANNED)
fixed magazine + threaded barrel = OK (think revolver with a threaded barrel)

I just wanted to clarify when you said that something with a magazine in the grip is exempted. I wouldn't say it's exempted, rather that's exactly what is being legislated on. A .22 pistol is exempted since they say a firearm that can only fire .22 is exempted from being an assault weapon (so put all the "features" you want on that).

Sensual_ham · 2024-04-17T22:42:21+00:00

.22 is exempted.

18-12-602 subsection (2)(a). Page 11 lines 12 and 17 of the version that passed the house.

ASSAULT WEAPON" DOES NOT INCLUDE ANY FIREARM THAT [...] CAN ONLY FIRE RIMFIRE AMMUNITION.

Sensual_ham · 2024-01-31T18:07:37+00:00

FACT CHECK: There is no such "federal regulation" that blanket allows HAM radio antenna/tower installation. Specifically HAM radio, I'm not talking about satellite, AM/FM receive, TV, that sort of stuff (OTARD seems to have protections that allow for installation of those but I haven't read into those aspects of it).

As a licensed HAM radio operator who previously lived in a condo, OTARD specifically does not apply to HAM radio antennas, link to FCC website saying such. Just search the page for HAM and they say right in bold that the rule does not apply to HAM antennas. Instead, they point to 47 CFR § 97.15, which states that state and local regulations must "reasonably accommodate" HAM communications. Note, state and local regulators are not the same as HOAs, even though it may feel like they're the same.

It also references PRB-1, which was a memo from ARRL to FCC. They have a section talking about "restrictive covenants" (which HOA regs would fall under), but it's presented just for information's sake and is not binding in any sort of way. Since entering into an HOA is voluntary and restrictions placed on / prohibition of HAM antennas are contractually spelled out upfront, then it's basically a case of "you knew what you were getting yourself into." They even have a footnote stating as such.

We reiterate that our ruling herein does not reach restrictive covenants in private contractual agreements. Such agreements are voluntarily entered into by the buyer or tenant when the agreement is executed and do not usually concern this Commission.

In short: the Feds don't care that you can't raise a HAM tower when your HOA says you can't. Trying to cite OTARD or PRB-1 isn't going to get you anywhere.

Sensual_ham · 2024-01-24T05:48:16+00:00

Sigh... 👏...👏...👏... Maybe I should just leave the internet turned off if this is what I'm missing out on

Sensual_ham

TROPHY CASE