I'm going to be getting a compressor soon, for routine work in my home shop. Nothing huge, just a basic 25-35 gal., 5-7 CFM rig. I've used gas and electric power tools all my life, but just happen to know utterly nothing about air tools.
My question is, how do you control the torque on an impact wrench? For example, one of the compressor's uses will be for rotating tires on the 5 family vehicles I maintain. That's a lotta lug nuts. The torque spec for those is around 60-70 ft. lbs., but a good 1/2" impact wrench, according to the label, can produce up to 750 ft. lbs.!! Some just have a "low - medium - high" switch on the grip.
Wouldn't that strip the nuts instantly? Isn't there some way to adjust the torque, so it would just tighten nuts down to that torque and then quit or slip? Or do you use the impact wrench to just spin it down, then hand-torque it? I see guys changing tires in commercial garages with impact wrenches, WRRRAP, WRRRAP, WRRRAP, and they're finished. Are they just guessing at the torque or something?
Sorry if this is a dumb question; I'm just at a loss here, can somebody fill me in on this?
On all of my impact wrenches, the trigger is just an on off switch, so this idea of pressing the switch lightly doesn't work. there is a dial on the base of the handle that sets the amount of air, and is a rough setting of torque. The claim of 750 ft lbs is pretty much if you sit there for a day or so hammering at max pressure. there are a lot of people who claim that your brake discs will warp instantly if you bring an air gun near your car, but I always wonder what about all of the discs that are bolted to the back of the hub, not slipped on over the studs? In any case, I seem to use the gun to spin down the nuts and hand torque on my race cars, and just let the gun do the tightening on all of my street vehicles.
I'd say most of the guys in the "commercial garages" are guessing. When I've checked the lugs after leaving such a place, they are usually way over tight and sometimes not tight enough. They typically use standard sockets.
Supposedly you can use a torque stick (found this web site
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to accurately torque nuts. Can't say if it worksor not. With regard to a gun rated 750 ft lbs, that would be at somepressure. You can limit this by using a lower pressure.
I use my impact wrench on the lowest setting to spin on the wheel nuts and then finish by using a torque wrench. Absolutely don't trust torquing them on with the impact! When your stuck on the side of the road with a flat sometime you won't have the benefit of your impact wrench to remove the over-torqued wheel nuts!
With the exception of the comment on how hard you squeeze the trigger will determine torque output of an impact wrench, the rest of the advice given here was very good. My advice is to NEVER use a impact wrench to torque (or final tighten) any nut lest you strip the threads as you surmised. You can use the impact to carefully spin the nut on faster than normal, but you should always stop short and finish up by hand with a torque wrench, not an impact wrench at some arbitrary/unknown value.
I had to prove to a shop monkey that you can't rely on an impact wrench to "torque" with anything near the correct setting. After breaking two extension bars trying to remove lug nuts that a shop had just put on (I was going to hand-torque them because the shop didn't "own" a torque wrench), I went back to the shop and had the guy try to remove a lug nut with a (clicking-type) torque wrench (well what do you know, they did "own" a torque wrench after all, A$$holes). He set it to 100lb-fts, turned it to remove the lug nut and it clicked, he then proclaimed that is was indeed at 100ft-lbs. I reminded him that that only proved the lug nut was at least 100ft-lbs and to keep going. Oh yeah, he said, so he tried 150ft-lbs, click, then 200ft-lbs, click, then the max setting of 250ft-lbs and click. So I made a monkey out of him, well so he already was one. So I asked him to remove all of the lug nuts and hand-torque them to 100ft-lbs (oh, I should have mentioned that I did not own an air compressor at the time, otherwise I would have just done it myself).
As for advice on an air compressor, you should get one as powerful as you can afford. If you're serious about this, you should consider getting one that runs on 220V power (vs. 110V), they are more efficient than a compressor that runs on 110V power. I'm just barely satisfied with mine, it runs on 220V AC power and runs tools up to 10.3 SCFM @90psi (mine has a max pressure of 125psi) and the tank size is 26gal. As for 750ft-lbs, only my 3/4" impact wrench claims that much torque, but I don't think that my lowly air compressor is capable of driving it properly, hence my comment of "barely satisfied". I only paid $300 (free shipping from HF) so I bought what I could afford and I feel that I got a pretty good setup.
Well, i don't know what wrenches you have been looking at. Most of the cheap ones are around 250lb or so. You can buy one of those at your discount place all day for $50 or less if you look. The better ones are usually in the 400 to 500 lbs range (1/2 drive were talking now). Most i have seen have a torque adjustment control separate from the trigger. I bought a higher torque husky from home depot for around $90. The IR's are good, but costly.
Make sure you buy good impact sockets to go with the air gun.
From what i have seen, get a belt drive unit. Preferable two stage. The direct drive units look cheap to me, and are noisy. Make sure you get a oiler, or regularly oil your tool before you use it.
Not only did they set the torque too high, they did not apply anti-seize compound on the threads, that`s obviously rusted. I was left with a nut that will spin in reverse but not come out. Not a hassle to a guy like me but will drive many folks up the wall. I'd just cut it off. Btw, did I mention a special tool is required to remove the hub to replace the bolt? Rick
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