Realistic max torque for impacts

[Mike83]

Ok, so most of the impact wrenches out there tout some astronomical value for max torque ("bolt breakaway torque"), but then give the "working torque" which can be considerably less. Is there some formula or consistent percentage of max torque that can be used to determine "working torque" i.e. this is what you can really expect from this wrench?

As a side note, what the hell bolt is torqued to 600 or 1,000 lb-ft that a 1/2" drive impact is used for? Is the big torque for busting rusty bolts loose?

 

[HolisticPerformance]

This is a great thread. I've been wanting to get these astronomical numbers figured out.

 

[gofastman]

Ok, so most of the impact wrenches out there tout some astronomical value for max torque ("bolt breakaway torque"), but then give the "working torque" which can be considerably less. Is there some formula or consistent percentage of max torque that can be used to determine "working torque" i.e. this is what you can really expect from this wrench?

As a side note, what the hell bolt is torqued to 600 or 1,000 lb-ft that a 1/2" drive impact is used for? Is the big torque for busting rusty bolts loose?

lets use an Snappy MG735 for example, it advertises 1090 ft lbs of max torque. This means it will break a bolt loose that has been tightened to that torque after several seconds of constant hammering, the working torque I believe is the "recommended" max torque you should work with in order to ensure long tool life, its like comparing RMS to max watts on a subwoofer. I wouldn't use any 1/2" impact to break loose 1000+ ft lb bolts on a regular basis.

 

[Monte]

The more Torque avertised the more sales...

 

[reversegear]

The more Torque avertised the more sales...

I have absolutely no idea what you are talking about.

 

[Ballistic Jello]

Have heard this explained as breakaway torque is the torque applied as the impact is first "fired" and working torque is the torque applied to the fastener thereafter, I don't know if that is accurate or not...comments? Honestly I find most of the the numbers and explanations a little fishy, although I have personally, not "heard of" or "read about" used the MG725 to remove lugs on a semi trailer, which are tightened with 1" tire guns generally rated at obscene torque numbers. This was fairly surprising to me, although it took 5 or 10 seconds for a few of them, I didn't expect it to happen it all.

Is there an independent tester like Consumer Reports for tools?

 

[jerk_chicken]

If we're talking in terms of friction, there's two types: Static and Kinetic. Both will have different coefficients, and I can definitely see them having an impact on needing to break away at a higher torque. It's as simple as that. Static friction is very high, and then once that force is overcome, you're in kinetic friction, which is lower.

1,000ft lbs? Some massive stretch bolts, maybe?

 

[eschoendorff]

I don 't really pay too much attention to manufacturers' torque claims. The IR 231 has significantly less torque than most of the newer gun on the market (400-450 compared with 500-600), but serves many techs very well on a daily basis.

My Snap On MG725 may or may not develop 600 or 700 ft/lbs of torque... I don't know and don't care. All I do care about is that is removes fasteners - which it does quite well.

 

[Mike83]

If we're talking in terms of friction, there's two types: Static and Kinetic. Both will have different coefficients, and I can definitely see them having an impact on needing to break away at a higher torque. It's as simple as that. Static friction is very high, and then once that force is overcome, you're in kinetic friction, which is lower.

1,000ft lbs? Some massive stretch bolts, maybe?

The reason why your torque wrench should be moving when it clicks.

Technically, if an impact wrench is "impacting", every hit would be overcoming static friction until the anvil spins the nut or bolt.