Mower blade bolt torque

[ghmerrill]

So here I am again about changes my blades in my old Howse mower. It's been a few years.

What do people tend to do in terms of the torque specs for bolts like these. The spec is 600 lb.-ft. I know that I can get to/above 600 lb.-ft. with my nice new Aircat 1150 (great tool!), but I can't MEASURE it. My torque wrench (automotive goes up only to 150). Even at the lowest setting on the 1150, it's above that.

What I've done previously is to put the nuts on at what seemed like "tight enough" with an impact wrench and not worried about. But this time I was wondering if I could at least approximate the "correct" torque.

What do other people do? Any thoughts? My guess is that pretty much everyone just wings it, but I'd like to know of any alternatives.

 

[RalphVa]

I use a 6 ft pipe that slips over a 3/4" socket handle. Just push on it until you cannot push any more, and it'll probably be close to 600 ft lb.

Mine's only 450 ft lb, but I tend to do the same thing.

Don't think it's rocket science on these big nuts.

Ralph

 

[TractorGuy]

For stuff like that I put a 6' pipe on a pull handle and lean on it with about half my weight. Okay maybe ALL my weight but that is only 165 lbs.

 

[TractorGuy]

Funny that two people were posting at the same time that use a 6' pipe. :laughing:

 

[WranglerX]

My favorite tool for high torque is "torgue multiplier"... Mine is 4:1 so my 150 ft-lb torque wrench will take torque up to 600 ft-lbs... Though torque multiplier is rated to go to 1000ft-lbs...

Input side is 1/2 inch drive, out put is 3/4 inch drive...

Dale

 

[TimberHole]

If you can get it vertical divide 600 by your body weight and that will give you the length of the wrench. Example: 600 ft/lbs / 200 lb body weight = a 3 wrench. Hang all your weight on a 3 horizontal wrench and you have 600 ft/lbs

 

[LD1]

Good half inch impact, hammer it til it quits.....good enough

 

[Maxify55]

I use the 1,2,3 ugga dugga measurement.
You can get a 400# gorilla to use his 4 ft pipe wrench OR
Whatever the impact driver delivers is close enough for me.

 

[5030]

I use a 6 ft pipe that slips over a 3/4" socket handle. Just push on it until you cannot push any more, and it'll probably be close to 600 ft lb.

Mine's only 450 ft lb, but I tend to do the same thing.

Don't think it's rocket science on these big nuts.

Ralph

Some 'big' nuts on this forum as well or should I say 'loose' nuts....:laughing:

 

[ghmerrill]

Thanks for the responses. They at least made me feel a bit better about not overlooking anything obvious.

I used to use the length of pipe and 3/4" breaker bar. But I was much younger then, and there are several problems with that. First, I have no way of actually measuring the result. So given that, I may as well use what I think seems like a reasonable application of an impact wrench.

Following up on that, I don't think there's any way to get confidence on how much torque you're applying with the pipe method. Yes, if you apply 100 lbs of force at the END of a 6' pipe, you get 600 lb.-ft. of torque. But you have to apply it at the END, and you have to know it's 100 lbs. You can't do that by any method of "leaning" into it. In part this is because the force needs to be in the same plane as the nut, and if your bar is horizontal (which it is unless you stand up the mower on its side) and unless you can somehow set it up so you are pulling straight, a lot of the force isn't going into that horizontal plane.

Setting up to apply that force in the horizontal plane is VERY tricky and requires fully stabilizing the mower so it doesn't, for example, swing on the hitch and doesn't move on whatever supports you're using. That's practically impossible. Again, given that, I'm at least as happy using an impact wrench that I've guestimated in terms of the torque it's producing. Also, given that I now have lumbar back problems (and successful surgery for that a year ago, but I don't want to invite more problems), I'm leery of having to pull with 100 lbs. or so of force.

What I decided to do in this case is to use the impact wrench at its lowest setting and see how that works. I expected that to produce a decent-looking result and then I might move up to the middle setting (maybe with reduced psi). But when I used the lowest setting, the nuts tightened to make the washers substantially, but not fully, compressed -- and so they're still exerting a locking effect. I'm thinking this is also at least an informal indication that the nut isn't overly tightened. So this is what I'm going with at this point, but will inspect things from time to time until I'm comfortable that there aren't any obvious problems.

 

[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.