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final closing force 1
- Thread starter 4648
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Hi 4648
We need to see what the fastener configuration is and also for the 120 degree turn we need the pitch of the screw thread to have any chance of calculating the final force.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
We need to see what the fastener configuration is and also for the 120 degree turn we need the pitch of the screw thread to have any chance of calculating the final force.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
SWComposites
Aerospace
and the stiffnesses of the joint members, and a bunch of other details.
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- #5
BrianPetersen
Mechanical
Are you looking for a prediction of the clamping force?
Why are you questioning the original manufacturer's assembly-procedure recommendations? Why do you need to know the clamping force as opposed to simply following the original manufacturer's recommendations?
Is it an assembly that is expected to be put together once and then never touched again, or is it something only expected to be taken apart and put together perhaps a small number of times in its entire life as part of (let's say) a major mechanical overhaul or maintenance procedure, or is it something that is expected to be taken apart and put together frequently?
Is it a torque-to-yield application? (Common tipoff is that the bolts have "always replace with new" as part of the service procedure)
Clamping force is notoriously variable depending upon installation conditions, hence the existence of service procedures that are less dependent upon someone setting a torque wrench. A torque-only service procedure needs to keep the fastener well below yield strength (in case someone lubricates the threads when they shouldn't, or uses a torque wrench that reads low) and well above the minimum required joint clamping force to allow for the huge uncertainty band (and that's fine, for a lot of applications). If it is a really critical installation, the most assured way of achieving a certain clamping force is to measure the stretch of the bolt, but this requires special tools. If it's somewhere in between, the torque-plus-angle method snugs up the bolt to take up the gap, and the low initial torque means it doesn't matter so much if someone makes a mistake high or low, and then the angle stretches the bolt by (in this case) somewhere approaching one-third of the thread pitch ... and this is an approximation, because part of that will be taken up by the bolt stretching, and part of it by the clamped part(s) compressing, and the rest of us have no knowledge of any of that.
Someone designed the bolted joint that you are working with. Ask them if you can deviate. Perhaps they'll explain you why you shouldn't!
Why are you questioning the original manufacturer's assembly-procedure recommendations? Why do you need to know the clamping force as opposed to simply following the original manufacturer's recommendations?
Is it an assembly that is expected to be put together once and then never touched again, or is it something only expected to be taken apart and put together perhaps a small number of times in its entire life as part of (let's say) a major mechanical overhaul or maintenance procedure, or is it something that is expected to be taken apart and put together frequently?
Is it a torque-to-yield application? (Common tipoff is that the bolts have "always replace with new" as part of the service procedure)
Clamping force is notoriously variable depending upon installation conditions, hence the existence of service procedures that are less dependent upon someone setting a torque wrench. A torque-only service procedure needs to keep the fastener well below yield strength (in case someone lubricates the threads when they shouldn't, or uses a torque wrench that reads low) and well above the minimum required joint clamping force to allow for the huge uncertainty band (and that's fine, for a lot of applications). If it is a really critical installation, the most assured way of achieving a certain clamping force is to measure the stretch of the bolt, but this requires special tools. If it's somewhere in between, the torque-plus-angle method snugs up the bolt to take up the gap, and the low initial torque means it doesn't matter so much if someone makes a mistake high or low, and then the angle stretches the bolt by (in this case) somewhere approaching one-third of the thread pitch ... and this is an approximation, because part of that will be taken up by the bolt stretching, and part of it by the clamped part(s) compressing, and the rest of us have no knowledge of any of that.
Someone designed the bolted joint that you are working with. Ask them if you can deviate. Perhaps they'll explain you why you shouldn't!
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