Impact gun ratings

[JHZR2]

Does anyone know at what point a rating from an impact gun is obtained? For example, if a gun has 360, 700, 100lb-ft of torque, is that measured after a certain number of impact events? Is the torque reported for impacting vs non-impacting with the handle held stationary and motor at full power?

I assume the numbers are at the strongest point of impact and full rotational speed?

Just curious with some of these highest rated guns, if it's easy to overpower a fastener enough to just shear off the head and not remove it.

 

[jmb3675]

Some impact wrenches list a max torque and some list working torque. Ingersoll Rand used to list a working torque but I am not sure if they still do. The cheaper makes usually list max torque which is usually only available the first few seconds the trigger is pulled as long as the air input is at the specified cfm rating. Twin hammer models usually have more power even if they have a little lower rating. I have a 600 foot ponund Snap on twin hammer that was made by Ingersoll Rand. For smaller bolts it will shear them off. I have broken bolts as thick as 1/2 an inch. But those most likely would have broken faster with a breaker bar. The Ingersoll Rand made tools have been the most reliable for me.

 

[jrmason]

There are at least 2 torque specs to look at when considering an impact. Max reverse torque and forward torque. Ingersoll lists both as a working torque but not all manufacturers do. You truly get what you pay for when talking impacts. We use Ingersoll exclusively at work from 1/2" up to 1" drive. We abuse them pretty heavily, sometimes running them for hours on end rattling hundreds of heavily rusted studs ranging from 3/4 up to 1-1/2 studs.

 

[Trav]

The other think to consider is the type of impact mechanism. A pin and clutch type develops high torque as soon as the trigger is pulled.
This type will easily shear off bolts quickly (depending on the diameter) but a 8mm manifold stud is no problem at all. This type is used in many cordless units for this very reason.

The twin hammer type is much more desirable and controllable for automotive use, torque is built up through continued hammering.
It might take quite a few hammers for it to reach its rated torque. The low settings let you rattle the fasteners loose on smaller diameter bolts and nuts.

 

[IndyIan]

An anecdotal rating for reference is my 250ftlb 7 amp corded Chinese mastercraft (Can tire house brand).
Semi over tightened lugs are not a problem with a 1 or 2 second hit. It was at its limit doing 12 year old rusty strut pinch bolts on the Neon which are torqued to 40ftlb plus 90 degrees.
I needed to hammer 2 seconds each way several times on most of them, but it got it done.
I think the A-arm bolts and the crank pulley bolts are the only higher torqued common fasteners than the strut pinch bolts on most cars, but I haven't had to try them.
I do notice that the torque does drop with a heavier socket with an extension which makes sense.
Can tire now makes a 350ftlb corded one which I would get if this one dies. I imagine it would do everything on a car(except crank pullty bolts) even using an extension.

 

[brages]

I would trust feedback on user forums more than any manufacturer's ratings.

 

[another Todd]

A big issue with air impacts is air delivery. Ratings are done at gun psi (90 or 100 usually) and unlimited volume at that psi. No shop duplicates this so you generally won't get the numbers they advertise. A 3/8 air hose which most shops use for a 1/2 impact, is usually adequate for a 1/2" gun, but not at all adequate for a 3/4 inch gun even with the pressure turned way up. You simply do not get enough air volume. I have 3/8 and 1/2 inch hoses with my 80 gallon compressor, and I can tell you there is a big difference in gun performance using the 1/2 inch hose, even with a 1/2 inch gun.