How much torque do I need on an impact wrench?

[drummerdimitri]

I'd like to get a pneumatic impact wrench for general metal fabrication and I'm not quite sure how much torque I would need for the majority of fastening applications.

I will only need to tighten down M12 bolts into tapped threads no deeper than 20 mm and at most M20 bolts fastened to nuts (very rarely if ever).

The bolt grades that will be used will vary from 4.8 to 8.8 and will be coarse grain.

Knowing this information, what would be the ideal max torque number for my application? I have no prior experience with pneumatic wrenches and hope the fastening torque can be adjusted somehow on either the tool itself or at least by lowering the input pressure (not ideal as that would also reduce the speed and BPM of the wrench).

Would this be an ideal one?

https://www.intlairtool.com/ingerso...mpact-wrench-15-000-rpm-332-ft-lb-max-torque/

 

[fsae0607]

If what you're torqueing down needs a specific torque value, maybe use a pneumatic ratchet and do final torque with a wrench.

Or something like these:

https://www.protoolreviews.com/trades/automotive/milwaukee-controlled-torque-impact-wrench/48575/

https://www.ingersollrand.com/en-us/power-tools/products/air-nutrunners.html

 

[Don1357]

Most impact wrenches will far exceed your needs. Maximum torque for 12.9 grade M12 is 123 foot-pound.

https://www.engineeringtoolbox.com/metric-bolts-maximum-torque-d_2054.html

The real question is how much CFM does your compressor pumps out. Impact wrenches are veritable air hogs; you may buy one capable of having a higher torque output but not be able to actually get it.

 

[sz0k30]

Don't know about that particular model, but I/R has always been considered the top of the line in impact wrenches.

 

[drummerdimitri]

Most impact wrenches will far exceed your needs. Maximum torque for 12.9 grade M12 is 123 foot-pound.

https://www.engineeringtoolbox.com/metric-bolts-maximum-torque-d_2054.html

The real question is how much CFM does your compressor pumps out. Impact wrenches are veritable air hogs; you may buy one capable of having a higher torque output but not be able to actually get it.

Surely that model would be more than enough for an M12 bolt, but what if I ever Go up to say an M20 bolt?

That model can only tighten it up to 251 ft-lb vs the 369 ft-lb MAX of the M20 bolt.

Does that mean I cannot or should not tighten down a M20 bolt to a nut with "only" 251 ft-lb of torque? That being said, keep in mind that the figures mentioned in that table is for the MAX and not recommended tightening torque.

My compressor provides 38.2 CFM of free air delivery so I should have no issues at all running the thing all day as this model only consumes 17 CFM of air.

 

[Buckaroo5]

Let me apologize in advance if I am missing the point.....The kind of torque wrench you are considering is used primarily to loosen bolts. If I had a large number of bolts to assemble, I would use something like the battery powered Milwaukee M12 Stubby which you has three settings or perhaps just a battery operated drill with a socket adapter.
https://www.harborfreight.com/hex-s...Yffmj4ogx7NTLnhuiAVb6oQ3AP7V2shwaApHgEALw_wcB
Finally, if you are looking to acheive a specific torque while tightening, you want to finish with something like this.....different ranges available.
https://www.tekton.com/3-8-inch-drive-click-torque-wrench-24330

 

[richfinn]

I would just go with a good quality 1/2" drive air impact wrench (any IR would be good in an industrial setting)

Then use Accutorq torque limiting sticks for whatever repetitive application you require!!!

 

[Rinspeed]

Specs for M12 bolts are less than 100 ft/lbs. I agree maybe an air ratchet is what you should be looking at.

 

[Jland]

My 1/2" IR 231c is over 700ft/lbs and while it is "adjustable" it is still a bit over kill on an m12.. my craftsman 3/8" is 75 ft/lbs max.. either way if you require a specific torque value you still need a torque wrench... 20mm isnt that thick and unless you are doing mass production, dozens of bolts one right after the other, you may be better off just running the bolt in by hand then torqueing it to spec

 

[drummerdimitri]

I have to make it clear that I am not looking to torque anything down to a specific value.

The tighter the better but so tight as to ruin the threads on the bolt or the nut!

 

[fsae0607]

I have to make it clear that I am not looking to torque anything down to a specific value.

The tighter the better but so tight as to ruin the threads on the bolt or the nut!

Air ratchet is best, then.

 

[richfinn]

I have to make it clear that I am not looking to torque anything down to a specific value.

The tighter the better but so tight as to ruin the threads on the bolt or the nut!

Thats why I recommend accutorq sticks, repeatable torque but you can run an impact wrench that will meet any future needs

Faster and more accurate than an air ratchet

 

[finn]

If this is an industrial assembly situation, you need an industrial driver with programmable torque control, not a homeowner or service garage consumer type impact.

If it’s a homeowner application with occasional use, an air ratchet will snug up the fastener, and you should use a manual torque wrench for final tightening.

Depends on how professional you want to be, and what the consequences of over or under tightening the fasteners in question are.

 

[drummerdimitri]

Thats why I recommend accutorq sticks, repeatable torque but you can run an impact wrench that will meet any future needs

Faster and more accurate than an air ratchet

Firstly, I have no easy access to purchase them and secondly, I would never bother with them as they are way too long to be useful.

That impact wrench has 4 power settings so I think I can get a feel for what is the correct tightness for each bolt size with time and experience as again, there is no specific requirement for how tightly torqued the bolts are, as long as they are not too loose or too tight, it should be good enough.

 

[drummerdimitri]

If this is an industrial assembly situation, you need an industrial driver with programmable torque control, not a homeowner or service garage consumer type impact.

If it’s a homeowner application with occasional use, an air ratchet will snug up the fastener, and you should use a manual torque wrench for final tightening.

Depends on how professional you want to be, and what the consequences of over or under tightening the fasteners in question are.

It will be used in a metal fab shop so not an industrial setting but a professional one.

Would a manual torque wrench be able to show me how tight a specific bolt is after being fastened using an impact wrench by loosening it?

Or do I need another type of tool to measure the breakaway torque of the fastened bolt?

 

[richfinn]

Firstly, I have no easy access to purchase them and secondly, I would never bother with them as they are way too long to be useful.

That impact wrench has 4 power settings so I think I can get a feel for what is the correct tightness for each bolt size with time and experience as again, there is no specific requirement for how tightly torqued the bolts are, as long as they are not too loose or too tight, it should be good enough.

Thats fair enough, just practice and you will get a feel for it thats what most of us older guys did with pneumatic impacts

Count the "Ugga Duggas"

I do like the Torque sticks for repetitive wheel bolt fastening, saves a lot of time and wear on tear on Torque wrenches, back in the 80s we just did it by feel though

 

[Rinspeed]

Sir.

 

[GeoBruin]

It will be used in a metal fab shop so not an industrial setting but a professional one.



Would a manual torque wrench be able to show me how tight a specific bolt is after being fastened using an impact wrench by loosening it?



Or do I need another type of tool to measure the breakaway torque of the fastened bolt?

So this is an interesting question. Theoretically you should be able to use the guess and check method. In other words, run your impact wrench to a certain number of impacts (or alligators if easier to count). Then set your torque wrench lower than you suspect the torque value to be and pull on it. If it clicks before turning the bolt, increase the value by 5 or so ft lbs and repeat. At some point, it will turn the bolt before it clicks. Now you have an approximate value.

Repeat the whole process a couple times and you should be able to zero in on a pretty narrow range.

I just scored a CDI Computorq 3 digital torqe wrench on Amazon Marketplace thanks to the "deals" forum here and one of the most useful things about it is being able to check the torque of fasteners that are already tight.

 

[finn]

It will be used in a metal fab shop so not an industrial setting but a professional one.

Would a manual torque wrench be able to show me how tight a specific bolt is after being fastened using an impact wrench by loosening it?

Or do I need another type of tool to measure the breakaway torque of the fastened bolt?

You can do a “break away and pull to mark” type audit, but unless you have some sort of torque control capable impact, the results will be operator dependent and all over the place.

You won’t have any consistency without some sort of torque control or torque/angle tool.

I just bought a new Milwaukee 1/2” impact that, I believe, has a torque control mode via Bluetooth to my cell phone. Haven’t investigated it, though.

 

[Leaflessshadetree]

I've been convinced many years ago that the guys doing tires at many stores have no problem overtorquing nuts with any impact (even with torque sticks).
These are guys tightening hundreds every day.

I have a few impacts and torque sticks. It isn't hard to overtorque (even with the stick).
I get a better feel with a 4 way (which is almost as quick), ratchet or breaker bar.
A torque wrench is going to be more accurate and consistant.