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Fastener Design Manual (1990) (nasa.gov)
39 points by polyterative 4 days ago | hide | past | favorite | 11 comments





Always amazing to know that there's a lifetime of work and knowledge behind the smallest tools. I guess for aerospace it requires it. The commentary along with the descriptions is pretty entertaining.

And at the other end of the spectrum, in our every day lives we probably just go to Home Depot, look for some screw/bolt and say, "eh, that's probably about right, huh?".


Technically, a bolt is a machine. (Wire rope is a machine too.)

The tighter your tolerances the more deeply you need to go into the details. For example, a hole drilled by a two-flute drill isn't round nor straight and to make it so you need to broach or bore it. You need to check how much out-of round it is and you do that with a three-point ID micrometer, since a two-flute drill makes a roughly triangular hole. Then for straighness you need a set of pin gauges...

The softer the material the less tolerances matter. This is why plastic is cheap and machine tools are expensive.


Most bolts in anything you buy have real engineering behind them. Most bolts you would use for stuff around the house will be way stronger than they need to be, or relatively benign when they fail.

I always feel a little bit guilty for not doing analysis on something I’m putting together, but it is so rarely a profitable or necessary use of my time when more than enough is so easy to do.


I have a brick walls in my house. I used dynobolts to put my TV mount on the wall. If I ever decide the floors is lava, and jump onto the wall grabbing my TV. I can be sure that those bolts will hold me. :D

But for everything else, there's those 3M glue hook things.


> I have a brick walls in my house. I used dynobolts to put my TV mount on the wall. If I ever decide the floors is lava, and jump onto the wall grabbing my TV. I can be sure that those bolts will hold me. :D

Don't be so sure. They may be rated to hold your weight under 1G of acceleration, but jumping onto the wall will apply a lot of jerk (j = ∆a), quite possibly exceeding the tolerances of the bolts or anchors (or more likely, that of the wall material they are anchored to, or even more likely, that of the mount or the TV itself).

You couldn't possibly prevail in a lawsuit against the manufacturer for failing to engineer the TV's mounting points to withstand an additional, say, 350-500lbs of force, however briefly applied, so it is probably safe to say that they are not too terribly likely to do so. Withstand it, that is.


Each bolt has something crazy like 1000kg shear rating and 300kg pull out. But yes, you're right the bricks would probably give out quicker than the bolts.

Maybe not even the brick per-se but the mortar, especially if it wasn't mixed correctly.

Non graded bolts you buy from the hardware store are usually built from cheddar cheese. But they're also used for super low loads so...

They call out those cheap, split lockwashers that have been experimentally proven to be ineffective: https://i.imgur.com/4nbgxmW.jpg

The lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a Iockwasher of this type is useless for locking.

Also, note this PDF was posted to HN six years ago: https://news.ycombinator.com/item?id=8604761


"ERRATA

The manual describes various platings that may be used for corrosion control including cadmium and zinc plating. It does not mention outgassing problems caused by the relatively high vapor pressure of these metals. The fastener manual was intended primarily for aeronautical applications, where outgassing is typically not a concern.

Issued June 17, 2008"

Heh. I wonder if there was a real incident that prompted the addition of this errata.





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