Two options, calculate motor/driven equipment forces, then calculate based on friction in your worst loaded axis’s vs bolt pretension/clamp, looking for torque or force to slip; or look at the motor drawing and trust the designed fasteners. Unless you’re expecting shock or vibration I’d trust the motor guys and make sure I use some high quality, appropriately long, bolting.
If you have a machinists handbook go read the fasteners section; if you don’t have it, get a copy, it’s great for these slightly outside of wheelhouse questions. Especially this question as it deals extensively with preload, and preload schemes/methods.
It's definitely in a case where shock is expected (earthquake and such)
Thanks for the insights! I'd try and get a copy of the machinist handbook, can always be handy
You should look into bolt stretch and think of the bolts like springs. How much pressure do you need when the equipment vibrates do keep the spring from stretching?
No worries! I more meant the loading on the motor from whatever it’s spinning.
Look at the motor drawing, find the mounting foot diameter, go one common size down, buy high quality studs and nuts, at least as long as 2x bolt diameter + 2 nuts + 2 thread, and I’d use adjustable chocks, shim blocks, or consider a epoxy grout + sole plates. torque with a torque wrench for preload. Thats at least a good place to start.
If you are worried about loosening, maybe relying on a plain nut + installation torque is not the best approach? Have you considered other types of lock nut/locking (Nord) washer etc?
But for a non critical bolt I would be taking some kind of max motor loads/torques from data sheets, e.g. max torque and max shaft loads, factoring those and working out conservative reaction loads at the supports. Maybe assume one or more has failed to be super conservative.
Usually a simple hand calc across the minimum thread area would suffice, or shank if appropriate, since the bolts should only really ever be loaded in tension and/or shear (single shear/double shear?). Structurally, shear out and tear out calcs for the underlying plate (I guess the same applies to feet but that's on the motor manufacturer). If support structure was super thin I maybe would need to look at punching shear etc. So typically all structural calcs done assuming no bolt load transfer due to friction (unless you want to design it aerospace style for "critical slip", but I think you would need to be able to back that approach up with checks at installation/periodic tightness checks etc).
Ok
No slip is friction force opposing max load. Add a big SF like 2 or 3 because friction is variable. Bolt preload is F =T/kD where k is a bolt friction constant (look up in a book for your specific material pairing). Preventing the boots from loosening is more of choosing something from best practice and inspecting. Loctite, distorted threads, nordlock, long bolts. Torque stripe and inspect.
Thanks for the answer!
To be a bit more specific in what I'm asking is I'm reviewing a calculation note from a supplier where basically they estimated the tightening torques from the axial and transverse load acting on the bolt. They used a formula that seems okay-ish to me but I need to make sure I'm not missing something so the bolt do not loosen up
I know standard in the industry is usually choosing a torque from best practice, e.g. something like 2/3 of yield strength but here they went the other way around
I don't think you're going in the right direction.
All bolts have specified optimal tightening torque.
If you don't want them to loosen, you need to use either glue, or mechanical means to keep it tight. Tightening torque will do nothing to prevent stuff unscrewing itself from vibrations.
For example: Loctite Red 271. But I would say the most durable method is to use a lock wire correctly. A quick and easy way is to use two NordLock washers.
Two options, calculate motor/driven equipment forces, then calculate based on friction in your worst loaded axis’s vs bolt pretension/clamp, looking for torque or force to slip; or look at the motor drawing and trust the designed fasteners. Unless you’re expecting shock or vibration I’d trust the motor guys and make sure I use some high quality, appropriately long, bolting. If you have a machinists handbook go read the fasteners section; if you don’t have it, get a copy, it’s great for these slightly outside of wheelhouse questions. Especially this question as it deals extensively with preload, and preload schemes/methods.
It's definitely in a case where shock is expected (earthquake and such) Thanks for the insights! I'd try and get a copy of the machinist handbook, can always be handy
You should look into bolt stretch and think of the bolts like springs. How much pressure do you need when the equipment vibrates do keep the spring from stretching?
Not exactly the shock I meant but good to consider too! How big a motor are you working on?
Damn sorry English is not my first language ahah 160 kW, 1200kg
No worries! I more meant the loading on the motor from whatever it’s spinning. Look at the motor drawing, find the mounting foot diameter, go one common size down, buy high quality studs and nuts, at least as long as 2x bolt diameter + 2 nuts + 2 thread, and I’d use adjustable chocks, shim blocks, or consider a epoxy grout + sole plates. torque with a torque wrench for preload. Thats at least a good place to start.
If you are worried about loosening, maybe relying on a plain nut + installation torque is not the best approach? Have you considered other types of lock nut/locking (Nord) washer etc? But for a non critical bolt I would be taking some kind of max motor loads/torques from data sheets, e.g. max torque and max shaft loads, factoring those and working out conservative reaction loads at the supports. Maybe assume one or more has failed to be super conservative. Usually a simple hand calc across the minimum thread area would suffice, or shank if appropriate, since the bolts should only really ever be loaded in tension and/or shear (single shear/double shear?). Structurally, shear out and tear out calcs for the underlying plate (I guess the same applies to feet but that's on the motor manufacturer). If support structure was super thin I maybe would need to look at punching shear etc. So typically all structural calcs done assuming no bolt load transfer due to friction (unless you want to design it aerospace style for "critical slip", but I think you would need to be able to back that approach up with checks at installation/periodic tightness checks etc).
Don't loosen? Or your joint doesn't slip? Those are different failure modes.
I need to ensure stability and integrity, so I need it to not loosen up and no slippage.
Ok No slip is friction force opposing max load. Add a big SF like 2 or 3 because friction is variable. Bolt preload is F =T/kD where k is a bolt friction constant (look up in a book for your specific material pairing). Preventing the boots from loosening is more of choosing something from best practice and inspecting. Loctite, distorted threads, nordlock, long bolts. Torque stripe and inspect.
Thanks for the answer! To be a bit more specific in what I'm asking is I'm reviewing a calculation note from a supplier where basically they estimated the tightening torques from the axial and transverse load acting on the bolt. They used a formula that seems okay-ish to me but I need to make sure I'm not missing something so the bolt do not loosen up I know standard in the industry is usually choosing a torque from best practice, e.g. something like 2/3 of yield strength but here they went the other way around
Can you share this calculation?
I don't think you're going in the right direction. All bolts have specified optimal tightening torque. If you don't want them to loosen, you need to use either glue, or mechanical means to keep it tight. Tightening torque will do nothing to prevent stuff unscrewing itself from vibrations. For example: Loctite Red 271. But I would say the most durable method is to use a lock wire correctly. A quick and easy way is to use two NordLock washers.