Impact wrench torque

I use a small air brake tank salvaged from a military water buffalo for just that. The tank is something like 6" in diameter and 8" long with ports on each bell end. I have quick disconnects on each end and the air wrench attaches right to the tank. I use this setup on my 3/4" impact and it makes ALL the difference. With this setup I don't have to upgrade my 3/8" air line for the 3/4" impact wrench. It's kinda neat listening to the tank refill after each trigger pull, which proves that the air line is undersized / overly restricted for the amount of air being demanded.

Shawn

On that IR impact, 3/8 fittings and 150psi WILL help. So will 1/2" hose at that length. The 2135 is a decent impact, but I still like my OLD CP better (can't remember for sure but I think it is a 734?) It is slower than the IR but I have found it more effective, while braking fewer studs. Just my experience.

I never reduced the pressure on my impacts from the 150 shop line pressure. Mine DID have a "power" adjustment that allowed me to dial the wrench back for assembling, and dial it up for dissassembling.

The 1000 ft lb spec is instantanious torque, not average or mean torque, and the high shock torque is what an "IMPACT" wrench is all about. And yes, if a 1/2" wheel stud is severely rusted to the nut, the impact WILL twist off the stud. So you punch it out and put in a new one, with a new nut. That's how the job has to be done sometimes.

The mass of the wrench absorbs the "instantanious torque" or "impact". Mean torque, or average torque, may be as little as 100-150 ft lbs and still have a 1000 ft lb rating - without stretching things at all (or very little)

Yabbut, yathinks wrong.

bernouli equations will give you the formal answer to your query - a less formal answer is 'pressure drop"

Because you're having a lot of air available upstream of a relatively short section that's only 1/4".

On Sat, 23 Feb 2008 21:07:01 -0500, with neither quill nor qualm, clare at snyder.on.ca quickly quoth:

That was deep and enlightening.

OK, checking online, CP (my recollection of the finest product) shows their top of the line 1/2" impact gun, the CP 749-2, putting out 625 ft# of torque. That amazes me.

I still think the 1000# is a bunch of marketing shit. Air gun technology doesn't appear to have changed much since I was using them on a daily basis.

OK, makes sense. Same theory as the traditional striking wrenches. But the wrench must be pretty heavy to achieve such a number.

But I still suspect that the 1000# may be a better measure of their marketing versus their impact wrenches. The instantaneous peak torque one will achieve will depend on how stiff the nut assembly in question is. I assume that this is measured while trying to twist a piece of hex stock welded to an anvil-sized hunk of iron. A better measure might be the rotational inertia of the hammer assembly plus the rotational speed at impact, combined into the angular momentum at impact. Such a measure would be more useful in deciding the relative strength of an impact wrench.

Hmm. The above metric won't work. A very light hammer moving fast will have a large angular momentum, but will be ineffectual in breaking stuck fasteners loose - the hammer will just bounce. The surface may become battered, but the nut won't turn. The hammer must be heavy, just as when using a handheld hammer to force something apart by banging on it.

Or a handheld hammer-activated impact wrench. I always used at least a two-pound hammer, sometimes five pound. The objective was to use a sufficiently large hammer that one blow would reliably do the job. This is how I got aluminum screws out of aluminum castings without damage, to get the alternator cover off of 1970s Japanese bikes. You got one chance before the #2 phillips screw was mangled beyond hope. They came loose with a very loud Crack!

This requires some thought. There must be a metric that captures the effect of hammer weight on effectiveness.

Joe Gwinn

We use an IR 2135 to remove the center lug nut on a Porsche. These get torqued to 340 foot pounds and left for a while, I figure breakaway torque is around 500 foot pounds for removal. It won't do that on the little compressor even if I charge it up to full 120 psi before pulling the trigger. We usually do that job off of a N2 bottle regulated at 150 psi. Even then it takes a few moments to see it start to loosen and move.

I suspect you need larger hoses. I have a 3" cutoff tool that runs f> I bought what is apparently the most powerful 1/2" drive impact wrench

How do you get accurate torque when assembling with an impact wrench?

The wheel nuts on my car require 81lb-ft of torque (put the wheels on today after a brake job) they assemble and disassemble easily by hand. A shop uses an impact wrench on them and they don't until they've undone them and re-done them with a torque wrench! The crankshaft pulley needs 200lb-ft. Also a manual job, just use a longer handle.

I can understand the use of an impact wrench for undoing truck wheel nuts, but with anything less than 400 lb-ft I would question the use of power tools for assembly. Much above that and I would be using a crane and balance. For large bolts, I would be expecting to use either hydraulic bolts or heated bolts and a micrometer, per the drawings.

Am I being excessively picky?

Mark Rand RTFM

The GOOD shops have a torque stick instead of an extension bar, it breaks loose at a specified (but somewhat inaccurate) measurement. Then torque it up properly by hand with a calibrated torque wrench. The mediocre shops use the torque stick alone. The bad shops have a bubble gum brain impact wrench jockey pull the trigger until it is "good and tight"

I d> On Sat, 23 Feb 2008 21:00:11 -0500, clare at snyder.on.ca wrote: >

Assembly with an impact is strictly a "speed" thing. With the proper "torque stick" and the proper technique, it is possible to "torque" a wheel nut accurately with an impact wrench(within less than 10%) I have, for decades, made a practice of putting the wheels on with the impact wrench, then going around and checking the torque on ALL the studs with the torque wrench before letting the car out of the shop.

I generally check my own vehicles again after 50-100 miles of driving.

On truck wheel nuts a "geared" torque wrench is often used (planetary drive multiplier)

Another factor is that the "wrench" which is struck benefits from being light, as long as it is sufficiently rigid. IIRC, these were advertised as being titanium, which is light but rigid. So make the part which is struck to transmit torque to the actual wrench socket as light as possible (titanium), and the hammer part as massive as possible (tungsten?) for maximum transfer of energy to the nut.

Enjoy, DoN.

I have seen shops use a torque wrench after an impact wrench but they only checked that the torque wrench would click in the tightening direction. In other words, they did not check that the lugs might already be too tight after using the impact wrench.

Effective use of a torque wrench in loosening tight fittings requires that the whole assembly be very rigid. It takes only a short extension or a thin socket to reduce the power significantly.

Don Young

when I pull those wheel nuts off my 356, I use a 3/4 inch breaker bar and a

There are "calibrated" extensions, too, that limit the torque by being of different diameters. Harbour freight probably sells them in the US, but I know that Princess Auto in Canada does.

Cheers Trevor Jones