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flex head torque wrench worth the $?

28K views 93 replies 18 participants last post by  Jon 
#1 ·
I am going to replace my old Sears torque wrench, am considering SK and was wondering of a flex head model is worth the premium on price, e.g. an SK 74251 1/2" 25-250 ft-lbs retails for about $83 and an SK 74256 flex head 1/2" 25-250 ft-lbs retails for about $137. It may be that other factors add to the price but I am unaware of them. How often is a flex head really handy and wouldn't using an extension work in most cases?
 
#3 ·
It is a myth that using an extension changes torque readings, that is as long as the extension is held straight and not allowed to lean over from the fastener. A crows foot type extension wrench will however change torque values and must be compensated for.
 
#5 ·
Mac torque wrench :thumbup:

As far as the flex head goes I personally can not remember a time when I could not finish a job for lack of one and in fact have never owned one but that is not to say they are not useful and maybe I have missed something.


that SK is a darn good wrench for the price.
 
#9 ·
I just bought a new torque wrench today after work. I was considering ordering a Snap On Tech wrench on line but at over $300 I decided to go for something a little cheaper. I bought a Beta torque wrench, they are Italian made and comes with an interchangeable head which will come in handy for torqueing down the centre bolts on an intake. It has a range of 30-150 ft/lbs which is great for just about everything I need to torque down. I got it at a great price, something like $180 US Dollars. I know I could have gotten a regular Snap On wrench for that price but after shipping costs to Europe and taxes the Beta was worth it.


http://www.photodump.com/direct/Canadian_Charlie/Bills073.jpg
 
#10 · (Edited by Moderator)
You need to talk to an engineer on the extension not affecting torque thing. That's not exactly true! While a short, stout extension won't affect torque a noticeable amount, the longer the extension, the more likely it is to affect torque. For small numbers, I'm guessing 50 lb/ft or so, it probably won't make enough difference to be concerned about if the extension is kept at 6" or less, 1/2" drive. With 3/8" better keep that to no more than 4". The longer and thinner an extension is, the more there will be some torsional flex. With a 6" 3/8" drive extension you might "lose" 2-3 lb/ft through (unnoticeable) twisting of the extnesion itself. Most fasteners won't mind the 2-3 lb/ft "loss", depends on how critical the torque is. Don't take any of these lengths and loss figures as gospel -- I'm guessing and using the "rules of thumb" I've picked up over the years. But extensions DO affect torque. Some machinists and/or engineering books will have a couple pages of formulas showing how to compensate.

I found this while searching for a good source, it's an engineer trying to be a bit humorous, but works!

That which gives you an offset position for the wrench from the
socket . .

For that we would have a torque loss equation . . .

You apply 50 ft-lbs of torque to a six inch extension to the
socket . . the extension is steel and steel is still the most
"elastic" material we have . . . .

Elasticity is defined as the amount of load that can be applied
to a material under certain constraints and the material will
return to its original shape . . .
Full text: http://www.type2.com/~keen/west/torque

This link: www.torqwrench.com/Info/FAQ.html has a chart with the formula used for an extension on the drive (between wrench and socket) and for change in length of wrench.

Make sure you click on this link too...
https://www.logsa.army.mil/WEB-PAGE/2001/586/586-55-57.pdf
 
#11 ·
Farna, this old wives tale has been argued for years and no an extension will not change the torque value. It does not matter if the extension flexes you would simply pull the wrench farther. It is simple laws of physics, whatever force you input into one end of that extension is what is going to be exerted on the other end period. If you were getting less energy out of it than you put into it where on earth does that energy go? If the extension twists then as I said the wrench would require that much more input as long as it is moving but when the torque setting is reached and movement is stopped then at that point the input force and the resistance is equal and that is what it will read. Now if you allow the extension to lean over from the center of the fastener so that the wrench turning center is no longer centered over the fastener then you would get an erroneous reading because of the leverage factor, but this is something else entirely. For this same reason a crows foot extension must be compensated for and some wrenches include a chart for doing this but again this is for leverage because the wrench is not centered over the fastener. If an extension required compensation then they would include that also.

Incidentally that link is refering to a crows foot wrench type extension not a long socket type extension.
 
#14 ·
An extension DOES affect Tq applied to a bolt.

I used to work in a tranny shop and just as the previous post said if you have 4 foot worth of extension your 400 ft/lb wrench won't Tq 75 ft/lbs.

I now work for a transport refrigeration company and the compressor heads are torqued to 23 ft/lbs on some models and 26 on others. We like to put a standard ratchet on the head bolts and see who can get closest with-out going over. Using a "click-it" style 3/8 Snap-on Tq wrench we then step up the Tq rating one ft/lb at a time until the bolt head turns. If a 6 inch extension is used we need one extra ft/lb at 28 ft/lbs {for the discharge manifold} to cause the bolt to turn again.

As a matter of fact they make special extensions just for impacts that will torque the rims on your car to a preset rating.


But this was about flex head tq wrenches. It seems to me that a flex head has the possibility to change the tq rating. If the wrench has been calibrated with a 24 inch handle and you need it at a 45* angle you have effectively reduced your leverage by 50% ....in otherwords if you are torquing a 100 ft/lb bolt with a 24" wrench you will need to pull a full 100 lbs of force on the handle as opposed to a 50 lb pull.{in addition to the fact that you have now increased the lateral strain on the bolt}.
Since the ratchet reads the tq from the handle side of the joint it will now read that 100 ft/lbs are being applied to the bolt head when in reality 50% of that, or 50 ft/lbs is being applied.
 
#15 · (Edited)
:rolleyes: Ok As I said this has been argued for years and disproved in many ways although some just will not accept common sense. Let's do a little physics.

One cannot argue with accepted laws of physics governing force such as "For every action there is an equal but opposite reaction" Thus if you apply a rotary force to one end of a shaft(in this case an extension) it will take an equal but opposite force (resistance in this case) to prevent the shaft from turning, no more no less. If the force is less on the other end the shaft would continue to spin but if it is more then it would turn in the opposite direction. If you use a shaft(extension) that is made of a material that will twist and then if you apply, say, 35 ft/lb of torque with a torque wrench then the wrench will read 35 ft/lb when it encounters that much resistance at the point of connection to the shaft(extension) then if the shaft(extension) "twists" under this much force it will simply have wound-up until it reached 35 ft/lb of resistance on the fastener end. Fellows like I said it is simple laws of physics and there is no way around it, Whatever force you put into one end of that extension is how much resistance it is going to take to stop it from turning and if you apply a turning force to one end of a shaft then it will turn until the resistance on the other end is EXACTLY equal, no more no less.
NXS If you allow an extension to tilt even slightly then you are dealing with the lever effect and that would affect the reading so it is important to keep this extension centered over the fastener and the impact extensions are dealing with impulse force and and is an entirely different matter. If what you guys are saying were true then a long bolt would require a different torque value than a short one but this is not true. And as far as saying that 400 ft/bs of torque applied to one end of a 4 ft extension will only amount to 75 lbs on the other end this is so ridiculous that it is almost comical and I would like to invite you down here to the mines where this is done all the time on certain mining equipment and you can explain to all these guys that they have been doing it wrong all these years and Caterpillar Tractor company does not know what it is talking about and needs to change it's service manuals! :)
Now take a look at that first link farna provided and check out the illustration and it shows the type of extension(wrench extension) that does affect torque values but if you had really checked it you would see that this(which really has nothing to do with what we are talking about) actually INCREASES the applied torque value from the torque wrench reading which is just the opposite of what you are saying. Also notice that although this is a list of factors that DO affect torque wrench readings there is no mention of socket extensions, Why not?
 
#17 · (Edited)
NXS, As I have already said about the extensions for an impact, That deals with IMPULSE force and has nothing to do with what we are talking about, we are dealing with CUMULATIVE force when using a torque wrench. You have apparently been searching for something to back up your point but I can predict that you are only finding info that deals with wrench type extensions that set the torque wrench off center of the fastener. You will search in vain trying to find credible info to back up what you are saying. you are also wrong about what you said about flex head torque wrenches, while it is true that changing the angle of the handle will affect the leverage by effectively changing the length it will only change the amount of force required to APPLY the desired torque reading but will have NO effect on the reading itself since this is a function of the amount of resistance encountered at the square drive connected to the fastener. Again go back to the link, so thoughtfully provided by Farna, and read what it says about handle length and you should plainly see why this would not affect the reading. An extension will have a profound effect on an impact wrench(impulse force) due to the fact it(the impact) must overcome inertial forces because of the mass of the extension and socket but once the force from the first blow is released this is lost and with each succeeding blow the cycle has to start all over again, this is the principle that those torque limiting impact extensions are based on but it has no effect on a torque wrench using a steady applied force. I trust you did notice that those extensions are for limiting torque only on impact wrenches? I honestly am not trying to be a smart$#% here it is just that this old tale has been bounced around for years, always with the same mistaken reasoning about extension flex but take an honest look at what you are saying and think about it. If a shaft is under tension from a twisting force how on earth could it have more force on one end than on the other? think about it. Any force induced into the extension, socket or any other attachment will be distributed equally over the entire length. Again, not tying to be a smart$#&, but by your reasoning of the spring absorbing applied(steady) force you could put springs on the soles of your shoes and make you bathroom scale read wrong.
Read what some of the other guys on the forum have to say about the subject.

www.hotrodders.com/forum/need-new-torque-wrench-38787.html
 
#18 ·
oldred said:
I would like to invite you down here to the mines where this is done all the time on certain mining equipment and you can explain to all these guys that they have been doing it wrong all these years and Caterpillar Tractor company does not know what it is talking about and needs to change it's service manuals! :)
I worked in an open faced mine (rock quarry) for 4 years on off road haul trucks and loaders. Not to mention heavy equipment dealerships like Komotso and John Deere. We used long extentions daily. You do need two people to do it correctly though. One to pull and one to hold the extension straight.
 
#19 ·
I agree the extention wont change the reading, or if it does its very little, I have used extentions to torque wheels, cylinder heads etc and not had a problem, and never once in school have they told us it changed values. I know my opinion isnt worth much since theres guys here that have been doing this longer than I've been alive but thats my 2 cents
 
#21 ·
This may seem like making a big deal out of nothing but there has been untold numbers of over-torqued and broken fasteners along with engine and equipment failure because of this very common myth. When a bolt is torqued to it's max and then the mechanic adds an extra 10% or so to make up for the "loss from using an extension" then the bolt is simply over-torqued by that much with predictable results. The odd thing is that using an extension can cause a false reading if allowed to tilt over from center but if that happens it will read LESS than the actual applied torque instead of more since the distance from the fastener center to the torque wrench drive center will provide leverage. Bottom line is using a socket extension PROPERLY will result in ZERO error. :)
 
#22 ·
I still think on a pivioting Tq wrench it will not read accurate if the handle is brought up to a 45* angle.
========
An extension reduces energy being transfered to the bolt guaranteed. Now wheter or not this actually changes the reading or not...it would seem unlikely but my experience has shown that it does. of course these were not scientific tests..but I can assure you that if an extension {socket extension, not breaker extension} is used more energy will be requred to reach a desired Tq.
 
#23 · (Edited)
NXS, -"an extension reduces energy being transfered to the bolt guaranteed"-- TRUE! (This statement says the same as the next)
--"I but I can assure you that if an extension(socket extension, not breaker extension) is used more energy will be required to reach a desired tq"-- TRUE!

Any extra ENERGY required to "twist" a springy extension will be added by simply pulling the wrench farther(tiny amount though it may be) this energy is then stored in the "spring" as static energy and will be released when the "spring" is allowed to relax. The TOTAL amount of ENERGY USED will not be absorbed by the bolt but the FORCE applied will be the same on each end! I think maybe the problem here is confusing APPLIED FORCE with TOTAL ENERGY used. If you want to think of it in terms of TOTAL ENERGY ok then think of it like this--amount of energy applied to fastener plus any energy absorbed by the spring(extension)=total ENERGY applied. But the "spring" cannot absorb more energy than it will take to "twist" it until it reaches equilibrium(resistance=force applied)at which point the balance of the total energy being used will be transferred to the fastener. If you still cannot understand what I am saying then You really need to brush up on elementary physical science and learn about levers and applied force.

The flex head torque wrench should be easy to understand if you will think about it. The torque reading is taken from the amount of resistance encountered at the square drive and has nothing to do with how the force is applied, The length of the handle only determines the amount of force needed to reach this resistance. Simply put if those things were in error when the handle is angled then they would include some sort of compensation method or just not make the dang things in the first place, surely you can understand that.
 
#24 ·
If a flex head torque wrench was not accurate I'm sure Snap-on and other companies woun't make them. It costs big amounts of money for the tooling to make these things and if they weren't accurate people woun't buy them and the tool companies would loose money.
 
#25 ·
Big Rat, I am well acquainted with the type of equipment you maintain and I am sure you run into using extensions and flex head type torque wrenches even more so than in auto work simply because of the sheer size of those things. I have worked on that sort of equipment(mostly welding)for over thirty years and I would not want to do anything else. We have maintained a fleet of 240 ton 830 Haul-Pacs along with various loaders, dozers, electric power shovels and other mining equipment. Demanding but interesting work :)
 
#26 ·
oldred said:
Big Rat, I am well acquainted with the type of equipment you maintain and I am sure you run into using extensions and flex head type torque wrenches even more so than in auto work simply because of the sheer size of those things. I have worked on that sort of equipment(mostly welding)for over thirty years and I would not want to do anything else. We have maintained a fleet of 240 ton 830 Haul-Pacs along with various loaders, dozers, electric power shovels and other mining equipment. Demanding but interesting work :)
The biggest trucks we had at the quarry were Cat 777 85 ton trucks, and I thought those were big. Your stuff are monsters. Since your a welder I hope you enjoy hardfacing, LOL!
 
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