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To little thread will the operator notice? 3

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Verkstad

Verkstad

Mechanical
May 17, 2011
44
If someone is using a torque wrench and there is to little thread and he hit the predrilled hole with the bolt. Will the guy using the torque wrench notice that? So that he can change bolt or add some thread?

I told our cheif engineer in a case that the thread will be too little if the schim would be zero and he claimed that the operator would notice.
 
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The rest of us have no context for the situation. I can guess what you are asking about, but I don't want to guess. Give us a diagram.

It's best to get it so that an operator can't make a mistake.
Or get it so that the foreseeable mistake doesn't have adverse consequences.
Failing that, detect the mistake on the assembly line via automated check fixture so that the incorrectly-assembled part doesn't get further down the line.
How much effort you put into this, depends on whether the consequence of the mistake is a squeaky interior trim panel, or a warranty claim for a fluid leak, or a catastrophic no-warning brake failure and people might die.
My background is automotive. Your situation may vary.
 
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A wrench with torque-turn measurement could detect the sudden change in stiffness. This is most noticeable if the fastener stops in the hole before any clamp load happens. It may not be noticed if it happens in the last 1 degree of turn.
 
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It is not mass production so everthing is done for hand. 1 degree can't be much.
 
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What do you mean “add some thread”

You really need to show some pictures and describe this joint in lots of detail.
 
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For manual then don't use a torque to install. Set a small torque and then switch to turning with a solid wrench by an amount that matches the elongation. If the head snaps off before it turns enough the installer will know they ran out of thread.
 
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Maybe. There's a partial thread between the tapped and pilot portion of a threaded hole, not a shoulder for the bolt to bottom against. Torque will increase slightly when the bolt reaches the partial thread and the threads slowly strip from the tip backwards, but the technician may or may not notice.
 
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I asume that a normal torque wrench cant detect it as well. It was more a general statement from him so it could be any joint critical or not.
 
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CWB1 but it that case you may still get s decent clamp force?
 
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If the bolt (screw in reality) bottoms out on the non-threaded hole before the plies are clamped together, the operator should notice the looseness in the clamped plies. Furthermore, a bottomed-out fastener sees torsional twist throughout the length, while a fastener that is holding torque at the top of the threads will not have the same amount of twist. Probably depends on the fastener length and the mechanic, in reality.

bolt_screw_pb74nf.png
 
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Will the guy using the torque wrench notice that?
Click to expand...

No, he will not.

The screw will stop turning.

The torque will increase.

The wrench will say "click".

The guy is happy.

Later, your thing fails in use.

 
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Verkstad,

If you cannot rely on your tapped holes to be deep enough for your screws, you are going to have to work out an inspection process. If your screw bottoms on the thread, your part will not be clamped.

Why are your holes not deep enough? Maybe you should be inspecting that.

--
JHG
 
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If you are lucky, the head of the bolt will snap off when it bottoms in the hole. Otherwise, you'll have an underclamped joint and possibly no indication of trouble.

Torque angle method is superior in this case as you won't achieve the angle of the fastener bottoms out.

You can add a washer or spacer under the head of the bolt if you think your holes are too shallow.
 
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Surprise side track: Saw a video about a spark plug hitting the piston in a leaf-blower. The fix was adding another washer pried from a spare spark plug. The cause was some weird accumulated deformation of the top of the piston; no overheat, 2 stroke with correct mixture, just some oddity in the alloy, probably crystal growth in the hotter thin center than the thicker surround. Extra washer for the win.
 
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+1 more vote stating that a torque wrench will not show if a bolt has bottomed out in threads vs. fully clamped the fastened member. The build-up of torque leaves no indication either - like a tapered pipe thread, a screw driving into incomplete threads gradually builds torque. The worst-case scenario is if the screw clamps the fastened member partially, so that the assembler won't notice any obvious looseness, but then under load the partial clamp load is overcome. Fix the length issue between the tapped holes and screws.

The cynic in me wants to know if your "chief engineer" also comes around with his torque wrench to check the torque on bolts he torqued with red loc-tite yesterday. Because that's another fallacy in using bolt torque.

 
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geesaman.d said:
The cynic in me wants to know if your "chief engineer" also comes around with his torque wrench to check the torque
Click to expand...

The cynic in me thinks that the chief engineer tells the production chief "You don't need to hire qualified assemblers or train the ones you do hire, because we design everything perfectly."
 
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