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Comment by lttlrck | Hacker News Reader

Smartbolts seem to be useful in applications where there is an expectation the bolts will loosen over time/the maintenance lifetime, reducing/easing inspection time.

Similar to the tell-tales used on truck lug nuts: https://www.dealsonwheels.co.nz/trucks/features/1302/new-tyr...

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Installing to a known torque and painting a line on the fastener is a lot less expensive, which becomes important when your project has potentially tens of thousands of key fasteners, like a bridge.

But for something like an MRI machine where there’s fewer fasteners and higher stakes - would make a lot of sense to use Smartbolt I think.

Tangential: related to trucks, there is a somewhat similar product to easily monitor tire pressure visually, which is popular: https://www.linkmfg.com/products/specialty-products/cats-eye

Yeah, a quality torque wrench isn't cheap (particularly the kind you find in fixed installations like auto repair shops and factories) but there's got to be some crossover when you are buying enough bolts that you're better spending money on tools that are more idiot proof.

Adding on to that, tensioning bolts using torque is convenient and inexpensive but not very accurate at all. Some data reproduced in Shigley's Mechanical Engineering Design showed a +/- 30% variation in tension for properly torqued bolts, if my memory is correct.

Emphasis on properly torqued: in the field threads or bolt heads might be dirty, or torque wrenches might be out of calibration, adding even more uncertainty.

A problem with many torque wrenches is that they click (or beep) when the set torque is reached, but they do not prevent tightening beyond that, nor do they have any way to indicate how much overtightened the fastener might be. It seems to me that these bolts have the same issue.

Ever wonder why the tire shop has tightened your wheel lug nuts so tight that you can't get them off with the hand wrench when you need to change a tire? They spin them on with a pneumatic impact wrench, and then "check" the torque with a torque wrench. Of course it clicks, because the nuts are already way too tight.

Slipper torque wrenches prevent over tightening

That explains a lot. Had a tire shop tighten the bolts on my old car so extremely tight that the threading on the bolts were broken. Every time I changed the tires after that I had to use a wrench with a looong bar attached to loosen the bolts (In Norwegian we call this a “latmannsarm which directly translates to lazy man arm, not sure what the English word would be). No matter how much grease or how much care I took to not tighten too hard the bolts were stuck next season. Glad the car is sold and not my problem anymore.

(I could of course have bought new bolts, but I always forgot about it after spending 2 hours changing the tires …)

in English we call that a Cheater bar, so it seems like that has carried across pretty well :)

https://en.wikipedia.org/wiki/Cheater_bar

AKA Cheater Pipe in Texas.

Not mentioned on that page, but you can make one out of two ordinary wrenches, which is both practical and may impress your friends! All I found online describing this was a video: https://youtu.be/5DShRItYxLA

A cheater bar or breaker bar.

Powered torque wrenches like Milwaulkee's (designed for electricians) and assembly line fastener drivers absolutely stop at the proper torque.

If you think dealership/tire shop/corner shop garage techs touch a torque wrench for lug nuts, you're dreaming. They blast each nut on with the gun and walk away.

Techs never are incentivized to get everything done as fast as possible because they're paid by book rate, and there's zero disincentive for not doing it properly.

Torque sticks were an attempt to address the problem but most techs can't even be bothered with those.

Proper torque for lug nuts is multi-step anyway. Star pattern partial tightening, with the wheel placed correctly on the hub if it doesn't have a concentric ring - then full tightening, then re-checking after the vehicle has been driven for a few minutes, because of fretting between the wheel, rotor, and hub surfaces...even if you've carefully prepped the surfaces, which again, no automotive tech does.

I install automated and semi-automated equipment in factories, sometimes including threaded fasteners, and the overwhelming majority of QC issues I observe (both on the devices being manufactured and on the mechanical equipment I'm delivering and writing code for) are not inaccuracies in torque or clamping load, but instead, failure to torque a bolt at all. The cycle was started but someone hit the E-stop mid cycle, and the fasteners were barely finger tight but you can't tell by looking at it.

A torque wrench is better than a Smartbolt once it's put on the fastener, but the Smartbolt can be measured just by looking at it.

An HN company does a similar thing with RFID tags for grease zerks:

https://greaseboss.com.au/

Again, it's not so much about measuring that the precisely right amount of grease was dispensed, but that every one of the 37 grease points was at least near the tip of the gun once every 30 days for the life of the equipment; the operator didn't forget about that one zerk that's hard to see and grease only 36 zerks for 5 years...

A problem with installation is that torque is only a proxy for tension. Torque alone is not incredibly accurate, so there are a lot of cases that could benefit from an easier way to accurately indicate tension than by externally measuring the stretch of the bolt (which often is not an option)

True, but this caveat is generally pre-empted in design phase through safety factor principles - multiply certain design parameters by a coefficient greater than 1 to account for the inaccuracy in things like torque-tension correlation.

I’m not getting your point here, won’t there always be inherent trade offs?

If you scale the specified torque, you risk over-tensioning.

If you scale the dimensions of the fastener, that has lots of consequences.

Is there some safety factor here you can add “for free” that I’m not seeing?

Otherwise, why is it that you “generally” pre-empt this caveat with safety factor versus coming up with a more reliable way to achieve the right tension?

The general idea is that proper bolt installation is a solved problem…at least in so far as ordinary industrial/commercial/construction applications are concerned. There’s an informed experienced trade base, a well established supply chain, and sound engineering practices already.

To put it another way, the right tension includes a safety factor. And engineering practice specifies testing and inspection and proven materials.

That safety factor and testing and inspection has costs associated with it.

Basically, it is a "solved problem" by designing things stronger than they have to be, and spending more on testing and inspection than necessary.

I'm sure the cases where these things are economical are fairly few, at least today, but if everyone took your attitude no progress would happen at all.

Safety factors; testing; and inspection are engineering.

The Smartbolt doesn't eliminate engineering.

More importantly, safety factors; testing; and inspection are progress. We have robust assemblies built first time based on rational analysis and formal processes. We have sky scrapers, suspension bridges, and space telescopes.

Obviously it doesn't eliminate all engineering. What it could do, though, is reduce costs. The idea is you could potentially achieve the same level of safety with less material or less testing.

Those things are progress in a sense, sure, but...

It's as if someone finds a way to make an alloy less prone to metal fatigue, and you just say "but you can use thicker metal, and test more." Sure, but.... well I don't see the point explaining this further to you, but I assume people reading this that don't see everything in black and white already understand.

Have you ever taken direct personal legal liability for structural fasteners as a licensed professional?

I have.

Does that give you the ability to have nuanced, big-picture, long-term view thinking?

You might as well argue that someone who works in a bank must understand macro-economics, or that someone in the military must have an excellent grasp of foreign policy.

You are steeped in the status quo. Your thinking on this is expected.

There's a fantastic set of two textbooks covering bolted joint design by John H. Bickford. One for gasketed assemblies and another for non-gasketed assemblies, if you want to really _really_ dive deep into it.

At the end of the day you get the final clamping force by multiplying a bunch of modification factors together that have been empirically measured and the bolting procedure has been verified. When you step outside any of the parameters you've verified in the past, you have to substantiate the math with experimental proof. The size of the fastener, fastener style (e.g., stud vs. bolt), fastener length, thread pitch, torquing method, presence of a washer, presence and type of lubricant, fastener material, base part material, and bolt arrangement ALL play into the final bolt assembly procedure. A lot of these are well-known and published.

Nobody is out there on assemblies like this just slinging unsubstantiated numbers around, at least if they're doing their due diligence.

Even where you can't measure the stretch directly, torque-plus-angle is a better way to achieve consistent stretch than torque alone.

In case anyone else needs to look this up, torque-plus-angle means seating the threaded fastener to a base torque, and achieving the target tension from there by further turning the fastener a specified angle. So super duper simple and something that many of us have done instinctively or from instructions, now we know there is a term for this general technique. Cf https://dannysengineportal.com/torque-specification-torque-t...

So "tighten till you hear a crack, then back a quarter turn" has merit after all?

Yes, though instead of the bolt or part cracking it's the click of the torque wrench, and you're going a quarter turn extra not back.

So really the exact opposite.

Well often nowadays it is torque+angle:

https://www.srtorque.com/error-proofing-tools/digital-torque...

If you look at a tire from the side, you can precisely see the bulge of the tire, which I do all the time to check the pressure.

This isn't generally true. Run flat tires have stiffer sidewalls and don't bulge.

Obviously, I don't have run flat tires. My tires bulge when the pressure is low.

This is a common problem is aerospace with obvious potential for bad consequences. The general approach is safety wiring.[1]

[1] https://en.m.wikipedia.org/wiki/Safety_wire

Torquing to a known torque and painting marks is fine...except there's no guarantee the clamp load hasn't changed due to all the mating surfaces wearing.

There's also too many variables in the real world if the application is critical enough. Clamp load changes with how many times the fasteners have been assembled due to the threads getting polished, how clean and dry the fasteners are, etc.

> painting a line

what if the bolt doesn't actually turn any, but the material itself stretches and loses tension?

I need these in my garage door. I wonder how much more expensive they are.

Edit: way too expensive.

https://www.mcmaster.com/smart-bolts/

$26+ each? Now I am curious which applications it does make sense to use these in.

Ah; so that's what those are for. I've seen them on lorry wheels, but never got around to formulating a sensible query for a search engine. These becoming commonplace seems like a recent thing (as in last decade or so).

Except that black == good == red + dirt/grime/grease.

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