I've found plenty of threads about torque wrenches doing a search, but since I don't have a great deal of time to read through them all, I'm asking for a few opinions and/or facts about your experiences.

I'm needing a torque wrench that can reach up to 250 ft-lbs and is reliable for a professional use environment. I currently own 2 Craftsman micro-clicker torque wrenches that have proven reliable so far (though I've only been using them for a few months) but the highest I get from them is 150 ft-lbs.

I'm sure the story is the same as with most tools - you get what you pay for - but I don't want to spend $100 or more only to find that it's not what I thought I was paying for. I'm willing to purchase the higher end tools (Snap On, Mac, etc) but if that's really the only way to go, I need time to save for them.

I've considered getting a digital torque wrench (either an actual wrench or an adapter) but my primary concern with these is a simple one - if it relies on a battery, then it's only as good as the battery that's in it. To put it another way - will it be as accurate when the battery only has 50% of it's charge versus when the battery has 80% of it's charge (those are random numbers - I didn't find any such specifications). To provide yet another way of looking at it, think of the starting system on your car - the battery needs to maintain a certain charge in order to operate the starting and ignition system - if it's below that charge, what do you get? Hard, slow, or no cranking at all.

I'm not willing to risk a repair on a customer car because of this potential issue, and finding literature about this problem is difficult to say the least (for a not-so-savvy internet adventurer such as myself).

There's 2 main styles of digital torque wrenches I've found:

1) Buzzer/Beeper - My hearing isn't the best, and any level of background noise (power tools, radio, even casual conversation) makes my hearing worse so I'm hesitant to rely on this style.

2) Clicker style with digital setting - I like the idea of digital accuracy with a clicker type feel, but I'm back to the same issue I already explained - it seems this is only as accurate as the battery that's in it.

So has anybody had any experience with the digital wrenches not being able to maintain accuracy depending on the state of the battery? If so, what have you done to compensate and/or maintain the accuracy?

Thanks.

 

HI,
I'm not any kind of serious mechanic, and my torque wrenches are the old beam style, but I have a few thoughts.

I looked at a 1/2 inch clicker at Sears, and I doubt that the battery would be the main issue -- or even very much of an issue at all. It looks like you turn the adjusting **** and the electronics just notes how far you've turned it. Probably by counting blips on some kind of index wheel or something like that.

So, the display will be correct until the battery starts to get pretty low. It probably even has an indicator to tell you when to change it.

As far as accuracy. the click mechanism is all mechanical as far as I can tell. Probably the same general gadget that was used when you read the setting by the lines on the shaft.

From what I've read and heard, this could be more of a problem. You do want to read about what is should be set at when you're NOT using it ( probably zero). Maybe some actual knowledgeable person will chime in on that.

Also, the mechanism does include some relatively small parts -- compared to the old beam type. From what I've read, the beam types are good pretty much forever, if they don't get a good whack. The clickers can start to drift as parts wear out.

Possibly you can just check that. Somebody wrote about a way to do that -- but it was quite a while back. IIRC he used a weight at the end of a lever arm to provide the load. The arm could pivot at the other end, and he used a bolt so that he could reef on it with the torque wrench. When the weight just moved, he figured that he knew the torque. (weight x distance, but I don't know what he did about the weight of the arm).

If you made a rig similar to that, you could use it to check if it was staying the same as time went on. You could probably rig it so that you could move the weight back and forth to see how much it was changing. I'm not sure that I would trust it to provide an actal value, but it would tell you if things were changing.

good luck,

hj

ps I'm with you on the hearing. I have two quite expensive hearing aids, and I still feel like I'm listening to the announcer in a train station half of the time

 

There are calibration tools/gauges available for torque wrenches, but the prices can make anyone hesitant to buy one (the cheapest ones are more expensive than many torque wrenches). If you have a basic understanding of how torque is applied, a homemade jig could be useful.

The main reason I'm asking is because there's such a wide range of cost. I'm not trying to be as cheap as possible, but I don't want to unnecessarily spend too much money either.

I think I should just email some manufacturers and ask them about this.

Thanks.

 

Torque wrenches record the twisting of some internal member. There is no "digital" torque wrench; some internal Chinese analog/digital chip records the reading and displays it to four-place precision. You are introducing another source of error.

Do not confuse precision and accuracy.

Stay with the conventional needle units. Avoid high-tech horsecrap.

Semper Fi

 

Snap-On has a few digital torque wrenches that are actually 100% digital. They are not cheap, and I have seen one crack the LCD under high torque, which was not covered by warranty.
https://store.snapon.com/TechAngle-1...--P760213.aspx

 

Jared, I have a slight disagreement about the Snap-On wrenches. They may do all of the measurement electronically, but the basic sensor is analog. Not sure of the tech used, but there's either some sort of a force sensor or a mechanical displacement sensor. The output of that sensor is digitized by an A/D converter as CougarJohn mentioned, and it's digital beyond that.

I'm sure thaat it's a great wrench if you don't break the LCD. ( They should have covered that ).

 

As far as I know they use a force sensor like a digital scale uses. They give a readout of current torque and beep at the desired level. They can act either like a beam or click type, I actually want a 1/4" one for setting up axles. I've had to do quite a few lately.

 

They have a torsion member with a potentiometer attached. As the torque is applied, the member twists and the wiper arm moves up the resistor. The voltage is proportional to deflection. An A/D converter digitizes and you get a readout.

So you have two sources of error in a digital unit that you do not have in a needle-beam:
1) Accuracy in the conversion of twist to resistance in the pot and
2) State of the battery that feeds the top of the voltage divider.

 

Do you have a source for that information? The info I have says otherwise, and using that wrench it does not move enough to get any level of accuracy out of a potentiometer. It is guaranteed accurate to 2% from 20-100% settings, that is off by a maximum of 5 ft/lbs at max. My HF click type was off by 5ft/lbs from 20-50ft/lbs.

 

Six, I can't defend what I wrote above about the potentiometer after a twenty-minute search. I was quoting garage talk. So I withdraw what I said.

I would like to know the basic operating principle of digital torque wrenches and scales.

Semper Fi

 

There are two basic methods of measuring force, both are generally referred to as a strain gauge. An actual strain gauge is a foil sensor that is applied to a stressed member and then returns a reading based on how much that flexes. I believe that is what the Snap-on wrench uses. There is also the piezo electric sensor, which is a bit more finicky, but cheaper. A piezo crystal generates a voltage based on how hard it's compressed.

 

I just wanted to update on this since I've clearly missed a lot of conversation.

Shortly after my last post, I emailed Craftsman and AC Delco about the issue of the battery life affecting the accuracy of their torque wrenches.

I still haven't heard from either of them.

I think I'm gonna pursue Snap On, Mac and Matco on this issue and see if I get any answers from them.

 

Good, DB. This is a good thread.

There are things called Zener diodes which act as a voltage clamp. Any competent engineer would put one in the circuit to compensate for the loss of voltage from battery decay.

Let us know what they write back in answer to your sensible post.