Impact wrench design and nutbusting torque

[OilUzer]

I see several impact wrenches advertising that their nutbusting (Reverse/Breakaway) torque is almost twice as much of the forward torque.

For example the impact wrench can produce up to 600 lbf-ft of forward torque but the reverse (nutbusting) torque is listed 1100 or another one had ~200 lbf-ft of forward torque with ~450 of nutbusting (reverse/breakaway) torque.

putting marketing aside, are these impact wrenches designed to function differently (mechanically) in reverse direction? For example are they designed to apply more voltage or more impacts per minutes, etc. in reverse direction?

I am mainly interested in design and functionality of the tools rather than marketing. I know marketing can find a way to exaggerate the numbers but twice as much!?

 

[Jetronic]

More airflow i'm thinking. More direct path of airflow in forward direction. Didn't come across a 2x difference myself. correction, just looked up my goto pneumatic impact wrench and lefty loosey is 1400Nm, righty tighty 745Nm. Both numbers are an exaggeration though left seems more powerful than right

HAZET-WERK - Hermann Zerver GmbH & Co. KG

www.hazet.de

 

[AutoMechanic]

I don’t know. I haven’t seen to many like that though.

 

[ABN_CBT_ENGR]

Torque is torque- there is no such thing as reverse torque or nut busting torque or anything like that.

If one wants to really split hairs, the entire rating is a lie ( that's why these are called IMPACT wrenches, not torque wrenches)

The marketing comes in when they convert one force ( impact shock and inertia) into a measurement of torque which has no linear conversion factor.

The force of the hammer ( impact) continuously shocks the fastener until it hits the yield threshold ( either turn or shear)- that's not even in the same galaxy as torque in relation to work and force measurement.

That's why a torque setting on an impact gun is basically a good guesstimate that will change over time.

And in reality the "shock" (amplitude) of the strike has a value of rotational force ( not unlike a manual hammer wrench) the frequency ( speed of the hammering) has the governing effect on how much of that force is useful over a given time.

Like any other indirect conversion factor, its part science, part marketing and part make believe and subject to a wide variety of influences and influencers

 

[Rand]

"nut busting" (I laugh) torque is a made up unit.. similar to peak watts in car audio vs RMS watts.
it can be inflated and justified with marketingspeak.

Now some pnunematic type impact wrenches could indeed be optimized for reverse operation

but you see the same nut busting marketing inflation with battery impacts.


Sort of related but not the same argument:

Ryobi 300ft/lb impact fine for most lugnuts but wont remove lugbolts that corroded over the winter.. even though they were tightened to 100ft/lb.

If you stand on a breaker bar they will loosen way before 300 ft/lb is reached. ie 200lb force on an 18" breaker bar.

not all torque is created equal I guess??

FWIW: almost all car lugnuts will come off fast with my m12 stubby impact (250ft/lb) and if they dont I reach for the dewalt dcf899 that has 1100ft/lb nut busting torque, 700ft/lb torque.. nothing has made it grunt for more than .5s so far.. except for when I broke my impact socket with it.

 

[Trav]

That is exactly right thank you for posting that explanation. The other thing to consider with impact guns is the type of socket, thickness and weight of the socket and anything used between the drive on the tool to the socket is going to reduce the force exerted sometimes dramatically.
Having used impacts for the better part of my life I have a little experience with them and seen some unusual things. The IR 2135 got stuck just rattling away doing nothing when trying to remove a M19 nut with a long impact extension even though it was rated for well over 1000 ftlb.

The old 231 lump rated at 450 ftlb or less with the same socket and extension blasted it right off with ease and with hardly any rattling at all, how can this be? Bigger/heavier hammers, harder hitting.
The type of machanism play a huge roll also, most cordless use clutch type to make their high numbers, the best for automotive work is a double hammer, these usually have a lower rating on paper but a good quality unit will out perform the cordless in the real world.

 

[Ram02]

Nut busting torque is always good

 

[HangFire]

"There is no such thing as reverse torque or nut busting torque or anything like that."

Sure, but it is worth noting that many air impacts have a different reverse torque rating than tighten.

 

[jhellwig]

Some of my Milwaukee’s have a faster speed in reverse than forward. My guess is that is how they are doing it.

 

[OilUzer]

I was looking at 18V impact wrench like Dewalt, Makita, etc. I own couple of Makita 18V impact drivers (less power than impact wrench) and Makita drill and I like them.

one of the impacts for example advertised 650 or 700 lbs-ft of torque with 1100 nutbusting (reverse) and another listed 200 torque with 400 reverse ...

I need to read what you guys said again or do some more research but if it's all about marketing and lies ... why wouldn't they say 400 forward torque and 400 nutbusting instead of 200 torque and 400 reverse? Or instead of 700/1100 why not say 800/1400?

sounds like there is more to it than just marketing. No? That's why I asked if they increase the number of impacts or duration of pulses or speed or higher applied voltage in reverse direction?

 

[Motu]

Try working on a truck with left hand wheel nuts on one side - you'll get the right hand side off no problems, but your impact gun will struggle on the left hand side, probably not even get them loose.

 

[CourierDriver]

Nut busting torque,,,,LMAOROF, you gotta love marketing terms, but then again, guys talk in those terms when jammed around the engine of a car telling war stories at a buddies house,,been going on since WW1 at least imho.. engine room, give me full speed, good day...Goodnight Paul Harvey where ever you are..

 

[ABN_CBT_ENGR]

why wouldn't they say 400 forward torque and 400 nutbusting instead of 200 torque and 400 reverse? Or instead of 700/1100 why not say 800/1400?

That question needs to be asked of them. They are the ones creating the "story" and selectively cherry picking and manipulating the data to basically support the claim enough to hopefully stave off any legal challenge if it ever happened. ( not dissimilar to an old case decades ago where someone sued McDonalds about their claim if "millions" served was somehow evidence of hoe much filler was in a patty because like this subject- theres no direct line between a hamburger and the amount of filler in the patty)

That's why I asked if they increase the number of impacts or duration of pulses or speed or higher applied voltage in reverse direction?

First, forward and reverse don't exist in rotation- they exist in displacement along a path relative to a scale. CW and CCW exist in rotation. ( neither the impact wrench nor the manufacturer could possibly know if you are using their tool on a RH or LH thread so FWD and REV are meaningless market hype geared toward a standard mechanic's level of understanding and not the actual science of the subject)

For the tool ( and this is very high level and general as each different design has an infinite number of ways to accomplish this and change percentages)

The "prime mover" ( power source) be it electricity, air, hydraulic or muscle does two separate and unequal things in tandem at the same time.

An RPM and speed is designed at a level of work (HP) and this is the torque. ( this can be variable, set, degreed or whatever the designer wants) Torque is born dynamic (turning force- if it aint turning, there is no torque)- that's part 1

Part 2 is the hammer set up ( in terms of mass, angles, surface contact, frequency and amplitude) ( Again, innumerable ways to do this)

Put them in the blender you have a relatively constant RPM/torque ratio ( torque to RPM is relative like voltage is to amperage) with a continuous hammering to shock things loose ( some can even be strong enough to create a gap by egg shaping a hex nut for a microsecond in an elastic moment loosening mechanical forces)

Since those 2 are somewhat unpredictable they cant both me measured reliably. Then since they are radically different- they both cant be exactly correlated together in any legitimate way.

The final result is a marketers dream- it can say whatever they want it to with enough anecdotal proof to survive most general level questioning. ( which is where their target market group lives)

Hope that helps explain it better ( a very general one because much deeper would almost have to be against a specific design or model given the number of possible variations to the above)

 

[Job]

There is a reason buried inside the tool depending on the designers. It’s interesting very high torque may be required to separate two glued pieces but a tap with a hard object knocks it apart. Just using pressure the two pieces may even break before the glue does. I used to twist off screws in wood work a lot with regular drills. Then a few years ago i discovered impact drivers and they can remove amazingly tight or damaged screws like it’s nothing with no damage. if you squeeze a ceramic with your hands it will stay intact but a light tap with a hammer shatters it. Thats how i disposed easily of several toilets, they just break into small pieces with no effort with taps from a hammer. Another example is the loud crack when a tight bolt releases, and then its easy. The wrench stands there, then the crack of the bond, then the torque required goes down dramatically.