Aproximating nut torque

[enginesrus]

thread404-107427

I'm being a bit lazy, its just easier to ask, and maybe someone has some fancy computer simulation software to nail it. I am jumping the gun though since I do not have the thread pitch and diameter just yet.
I have two items that I have to torque nuts on with no easy way to hold them to use any sort of lever wrench on, I can only use an impact wrench. So I can load the nut down maybe only a few inch lbs not sure how many yet, and then torque turn to get into the 185 to 200 ft lbs region. Any quick formula to accomplish that?

 

[MacGyverS2000]

Calculate what? Torque is torque, even if the nut slips a bit until you get some bite... but once it bites, the torque measures the same.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[hydtools]

Your goal is fastener tension, joint clamp load. Torque is an indirect means to achieve that. Research torque-indicating nut runners, for example.

Ted

 

[Tmoose]

AFF Torque Limited Socket, 1/2" Drive, 19mm, 180 ft/lbs, Yellow Gray, 40217

 

[kjoiner]

Hello,

Another possible option for impact wrenches is torque sticks. They look like extensions and are color coded and engraved with the torque rating. They work by flexing and defeating the ability of the impact wrench to deliver more torque than the rating of the stick:

https://www.kentool.com/product-category/wrench-products/torque-master-torque-sticks-extensions/

Kyle

 

[TugboatEng]

I had a situation where I needed to torque a fastener with no clearance to use torque tools. I measured the grip length and used shims to create the same grip length on my work bench. I snugged everything up and then torqued to produce an angle measurement. Then, on the boat, I snugged up the fasteners and then ran the nuts to that same angle from the workbench.

 

[dvd]

Use turn-of-nut method -

https://www.portlandbolt.com/technical/faqs/turn-nut-method/

 

[TugboatEng]

You can also torque to yield. A good operator will be able to feel the yield point without tools.

 

[enginesrus]

Okay, not torque. The proper tension that would equal the call out torque that the manual specifys. I will have to get the proper measurements of thread diameter and pitch.
Its a vector loading deal of sorts, I guess I'll just have to pull out the machinerys hand book and do some calculations. So much of the turn distance will give a certain amount of pressure.
This is not a bolt it is a shaft of sorts with no way to hold it unless I had the manufactures fixturing to do it. Every one that works on these things just air impacts till they think its good enough. I'd just like more accuracy thats all.

 

[TugboatEng]

We used to torque head bolts on diesel engines. Now everything is done with impact wrenches per dvd's comment. I actually prefer the impact method as it provides a more accurate result. Sometimes the bolt holes get debris at the bottom and a torque wrench will qualify while an impact wrench won't make the required rotation.

 

[rather_be_riding]

I find the tribology online calculator to be pretty decent if you're wanting to skip the Machinery's (or sanity check your work). Engineering toolbox offers a simplified version that makes some assumptions regarding pitch etc.

Tribology online calculator
Engineering Toolbox calculator

 

[enginesrus]

With all the fancy FEA and other simulation software etc. I'm surprised that if I give the few variables that someone couldn't just tap a few keys and have it. I have always said what a joke all the fancy computer
stuff is, and how the old ways of doing things seem better and more accurate, time consuming, yes. Just can't beat those old time engineers in the WW2 days, just look at what they accomplished.

And Tugboat, the cat manuals always said not to use an impact wrench for the final torque turn, many of the goofs in their engine shops do that all the time.

 

[SwinnyGG]

I'm surprised that if I give the few variables that someone couldn't just tap a few keys and have it.

It is easy to calculate - you just haven't provided any specifics.

If you know the size of the fastener and the prescribed torque, you can estimate what the original fastener tension target was. There are numerous sources out there for the equations, such as:

https://www.engineeringtoolbox.com/bolt-torque-load-calculator-d_2065.html

Once you know what the tension target is, you can calculate how many turns you need to achieve that target, based on the fastener material/size/thread pitch.

None of this will be very precise, because you have to make assumptions about things like the coefficient of friction between components and the like. But it will be more precise than guessing at how long to hold down the trigger of the impact gun.

 

[IRstuff]

Isn't that uncertainty about friction one reason there's often a recommendation to lubricate?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

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[SwinnyGG]

Yup. It'll help make this educated guess a better one too if everything is lubricated.

 

[enginesrus]

So far the dimensions are this. Across the threads OD 1.176 so must be 30mm, the pitch is 1mm.
Have searched and found nothing about even a recommended torque for that size. There is a call out of 185 ft lbs given for a similar nut and thread on another shaft nothing for this one.
It will be lubricated.

 

[SwinnyGG]

With that information and the equations above, you have everything you need.

 

[onatirec]

OP you need to do some basic reading on bolted joints, e.g. Shigleys Mechanical Engineering Design or Machinery's Handbook. It's apparent that you don't know enough to develop a good question - which is ok, but don't blame everybody else since you don't know how to tap a few keys for your answer.

What you are trying to achieve is a particular preload at the bolted connection. This preload depends on a few things, primarily (I'd suggest) bolt strength. Of course you don't want to apply more pressure than the bolted materials can handle. Unfortunately, measuring preload is generally much more difficult than measuring torque. The torque required to achieve your desired preload depends on bolt geometry and friction (as mentioned already in this thread).

That said, a simple equation for calculating the torque required for a particular preload is T = K*F*d, with d=nominal bolt diameter, F=preload, and K=friction factor depending on materials, lubrication, geometry, etc. K~0.2 is usually a reasonable value.

 

[IRstuff]

My understanding is that the preload is manifested as an elongation of the bolt, so measuring that will possibly give you a more accurate correlation to preload, assuming you don't deform the other joint materials.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[SwinnyGG]

My understanding is that the preload is manifested as an elongation of the bolt, so measuring that will possibly give you a more accurate correlation to preload, assuming you don't deform the other joint materials.

Not sure if you're downplaying what you know.. ha ha. But right again.

This is how you can get to a preload estimate just from counting turns... if you know thread pitch, you know how many turns it takes to get X amount of stretch in your fastener. Assuming your clamped materials are infinitely stiff. Which is not accurate.