Mower blade bolt torque

[WranglerX]

Problem with impact wrenches is they are calibrated differently and unless tested and calibrated, you are just whistling in the wind... It like doing your lug nuts on your vehicles wheels, there is a recommended torque value, but any real shop will spin them on with air impact THEN use a torque wrench to be sure it meets the vehicles recommendation... Also another variable to impacts is air pressure

I have three air impacts (two 1/2 inch and one 3/8 inch ) and don't have a clue as to what the are capable of torque wise...

Dale

 

[TimberHole]

I find most impacts hit about half as hard as the manufacturer claims. They almost claim 350 or better. A 3/4 diameter A325 structural bolt takes about 350 ft/lbs give or take. Few if any electric impacts will rattle that bolt.

 

[4570Man]

I find most impacts hit about half as hard as the manufacturer claims. They almost claim 350 or better. A 3/4 diameter A325 structural bolt takes about 350 ft/lbs give or take. Few if any electric impacts will rattle that bolt.

They might make their rating with the drive clamped tight in a collet. They loose a lot with the slop in a socket. With an extension it’s worse.

 

[TimberHole]

They might make their rating with the drive clamped tight in a collet. They loose a lot with the slop in a socket. With an extension it’s worse.

I have wondered how they are rated. If they are like most products today I doubt if they put much effort into it when they can just lie. Even using a decent impact socket snd holding the impact firmly is not going to come close to achieving their claims.

 

[ghmerrill]

Problem with impact wrenches is they are calibrated differently and unless tested and calibrated, you are just whistling in the wind... It like doing your lug nuts on your vehicles wheels, there is a recommended torque value, but any real shop will spin them on with air impact THEN use a torque wrench to be sure it meets the vehicles recommendation... Also another variable to impacts is air pressure

I have three air impacts (two 1/2 inch and one 3/8 inch ) and don't have a clue as to what the are capable of torque wise...

Dale

Agreed. However, I do have a small clue since I did indeed attempt to calibrate the settings with the torque wrench I have. Not surprisingly, the results are non-linear with respect to increases in psi. And of course the biggest problem for me is that is that my torque wrench maxes out at 140 lb.-ft. I may do some more of that because I SUSPECT that the psi vs. torque curve flattens with increase in psi (i.e., the first derivative approaches 0), but that's just a suspicion and more curiousity than usable knowledge. And projecting results into my currently non-testable range is at best shaky.

In thinking about these responses to my original query, I've also had another idea of how I can narrow down the range that I know the Aircat 1150 is producing torque in. I may experiment with that in anothe day or two, and if I do will post the results.

The real solution to the problem, while using an impact wrench, is a "torque socket" or "torque stick". But I'm reluctant to spend $100 on something that I'd use only (at most) every couple of years if I'm reasonably confident that I'm getting a result that's sufficiently close and safe. If it weren't for the virus situation I might try to go rent a hefty enough torque wrench to test my results. And I've been using this particular mower for over 25 years without incident, no matter how I've tightened those bolts. But it's good to get feedback from various other perspectives.

Sunex 534TE 1-Inch Drive 55-Feet/Pound Torque Truck Extension Bar - Torque Wrenches - Amazon.com

 

[TimberHole]

Easy to make your own test/calibration rig. Fix a bolt to a post and hang weight from a wrench to create the load. There is nothing more accurate. Weight x arm = moment. You can tighten a nut on your test rig with your impact then add weight weight to a wrench till the nut turns. That will give you a value just above the impact value.

 

[ghmerrill]

Easy to make your own test/calibration rig. Fix a bolt to a post and hang weight from a wrench to create the load. There is nothing more accurate. Weight x arm = moment. You can tighten a nut on your test rig with your impact then add weight weight to a wrench till the nut turns. That will give you a value just above the impact value.

It took me a while to see this. But I'm a little intimidated about finding the 600 lb. weight to hand on the wrench. I don't even have that much in my collection of tractor weights.

 

[4570Man]

It doesn’t have to be 600 pounds. It just needs to be a longer pipe than 1 foot.

 

[ghmerrill]

So today, since the weather's relatively pleasant this afternoon (88 degrees and 79% humidity :sarcastic, I got out the 3/4" breaker bar and the 7' pipe and tightened one of the nuts with that up to the point where I "felt" that I was close to applying 100 lbs to the bar at 6'. Then I set my wrench to its middle setting and the compressor to 75 psi.: it didn't budge the nut. Cranked up to 85: just a small fraction of a turn. Up to 90: it put about 3/4 of a turn on the nut and quit.

My "feeling" is that my middle torque setting with 90 psi at the wrench puts ~600 lb.-ft. on the nut, +/- some x which is "relatively small" -- or close enough anyway. While I managed to do this without screwing up my back, I think the next time around, I'll just leave out the pipe/breaker bar step.

 

[ghmerrill]

No pipe mentioned in the original description (threw me off a bit ), but yes, that will do the trick. But the contraption does get a bit unwieldy if you end up using something like a 6' pipe. Still, it's a good technique to keep in mind, and I do currently have a nice post for that apparatus in the center of an old riding ring we don't use any more.