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A reader recently asked if ToolGuyd can verify manufacturer’s cordless drill max torque specs.
I have considered this over the years, and it’s complicated. I’m thinking about it again, and brushed up on what this would require.
With cordless drills now delivering over 1000 in-lbs max torque, and impact wrenches delivering over 1000 ft-lbs max torque, specific equipment us needed.
Where Drill Torque Specs Come From
The Power Tool Institute – the industry group that most cordless power tool brands belong to – have guidelines as to how drill torque can be measured and advertised.
Their guidelines are very outdated, and nobody got back to me about whether they’ve updated their recommendations for drills that deliver above 1000 in-lbs max torque.
Anyway, there’s a set procedure that cordless power tool brands are presumed to follow for determining the max torque specs they put on a tool’s packaging. They’re voluntary guidelines, but I’d expect that all of the brands partnered in an industry group would adhere to them.
Max torque specs aren’t the most helpful metric in the world, but should be a consistent and a fair comparison point between different brands’ cordless drills and impact drivers.
Basic Torque Testers
Here’s a Gearwrench torque tester, available on Amazon. These are really meant for checking the calibration of torque wrenches and other such tools.
Some, like this one from AWS, are rated for use with continuous-drive tools – such as powered screwdrivers and possibly cordless drills – if used with a rundown adapter.
Rundown Adapters and Joint Simulators
Here’s a low-strength rundown adapter from Mountz.
Here’s a joint simulator rundown adapter from CDI.
Lower strength adapters tend to have springs, higher strength ones have stacks of belleville spring washers.
Here’s what belleville spring washers look like, courtesy of bellevillesprings.com. Compressing belleville washers requires a bit of force. Stack them up, and you can create a repeatable compressive load.
Joint simulators use stacks of these springs – sometimes in different configurations – to simulate real-world applications.
It’s not exactly the same, but offers a repeatable and somewhat controllable way to push a cordless drill to its maximum torque.
Types of Fastening Joints
There are two types of joints – hard joints and soft joints. Some joints are in between and have characteristics of both.
An example of a hard joint would be metal-to-metal fastening where a fraction of a turn takes a bolt from loose to tight. An example of a soft joint would be screwing wood to wood, where friction builds and the wood can compress. The resistive force builds as you turn tighten a fastener.
Some brands give their cordless drills both hard and soft joint max torque ratings. You’ll see that in European spec sheets, but rarely here in the USA. Here, we generally only see the highest rating of the two.
In theory, a rundown adapter or joint simulator can be used with any torque tester or transducer, but it seems like a better idea to use testers designed for use with such tools.
This limits things, but it’s not the only consideration.
What’s the testing range? For cordless drills, we would need capacities up to at least 1500 in-lbs. Modern cordless drills are rated up to 1400 in-lbs the last I checked, and it would be good to have some headroom.
But, the majority of cordless drills deliver less than 750 in-lbs of max torque.
As the torque testing range increases, so does the size of the transducer and its drive size or interface.
Is it the best idea to test a cordless drill rated to 400 in-lbs on a 2000 in-lbs tester?
If you can source or build an appropriately spec’ed and well-sized rundown adapter, it’s not a big deal. What you don’t want to do is have to add a stack of size adapters. The less you have between the tool and tester, aside for the rundown adapter or joint simulator, the better.
Most torque adapters are calibrated from 10% to the full value. What if we want to also test the torque clutch settings? A 2000 in-lbs transducer or tester might help us test a drill that is spec’ed to 1400 in-lbs max torque, but won’t provide accurate measurements below 200 in-lbs. For a 400 in-lb drill, we wouldn’t be able to test the torque across most of its adjustable clutch settings.
Torque Testing Accuracy
Accuracy is also an important consideration.
Some torque testers have accuracy values relative to indicated measurements. For such testers, a measurement of say 400 in-lbs max torque with 1% accuracy would actually be 400 ± 4 in-lbs.
Let’s say a different torque tester with 2000 in-lbs max testing limit is rated to 0.5% accuracy across the full scale. This would mean the 400 in-lbs measurement would be 400 ± 10 in-lbs. That ± 10 in-lbs component won’t change with the measurement.
So if you have two transducers, both with 2000 in-lbs max torque testing capabilities, one with ±1% accuracy relative to the measurement, and the other with ±0.5% accuracy relative to the full scale, there are different points in the range where one will yield more accurate measurements than the other.
What does ± mean for a value? Let’s say you have a measurement of 100 ± 5 in-lbs. This that the actual value could be between 95 and 105 in-lbs. There will also likely be an error due to the least significant digit, similar to how there’s an uncertainty when reading between markings in a ruler.
Impact Driver and Wrench Torque Testing
How do we test impact drivers or wrenches?
There are some models that can handle continuous rotation and impact action, but it would probably be best to go with something like the AWS IMP series of testers shown here. These have a very beefy torque transducer and rundown adapter, and a display that can work with other models of AWS torque testers.
These retail starting at $4K and according to the lead time I was given yesterday by a dealer, they’re backordered into at least early 2024. I asked AWS for lead times as well but haven’t heard back.
Selecting a Torque Tester
The CDI electronic torque tester that the Power Tool Institute specifies in their outdated torque measurement guidelines tops out at 1000 in-lbs. And it’s not rated for impact tools.
All of the impact-rated testers I’ve seen have full-scale accuracy values. Let’s say we test an impact driver on a tester designed to max out at 1000 ft-lbs, which still won’t accommodate brands’ top models. A 1% accuracy could then mean a measurement of say 1800 ± 120 in-lbs max torque.
1000 ft-lbs is 12,000 in-lbs. 1% full scale accuracy would then be 120 in-lbs.
Imada has a line of continuous and impact tool torque testers, as well as non-impact testers.
But… they have full scale accuracy, as opposed to measurement-relative. Their low-range model tops out at 440 in-lbs, their mid-range model tops out at 1740 in-lbs, and their higher-range model can measure up to 362 ft-lbs (4344 in-lbs) of torque.
The mid-range model should be able to handle most cordless drills, but with lower absolute value accuracy at the bottom end of the range, due to having a full scale accuracy rating. It also can’t test most 18V-class impact drivers, which exceed its torque testing limit. The higher range model can test impact drivers, but will lead to much lower accuracy when testing drills, especially lower powered ones.
If we have a drill that tests at 200 in-lbs, the accuracy on the high-range model would mean a measurement of 200 ± 22 in-lbs (due to ±0.5% accuracy based on the 4344 torque testing range), which is an unacceptably high uncertainty range in my opinion.
I should point out that Imada’s are among very few models that extend below the 10% of full range floor. In the case of the high-range model, it tests from 3 to 362 ft-lbs. Their mid-range model tests from 30 to 1740 in-lbs. Most other testers are not calibrated below 10% of the upper end of the range.
Why Not Use a Torque Adapter?
Why not just use something like this, an inexpensive torque adapter?
First, where’s the rundown adapter? Lots of YouTubers claim measurements, but without a joint simulator, those measurements can be wildly far-off and inaccurate. Second, they’re designed for use with manual torque wrenches. This one has an accuracy of ±2%.
What’s the rotational speed of a ratchet? What about a cordless drill?
Torque adapters are designed to be used in place of a torque wrench. They’re not designed for testing or calibrating the torque of manual or powered tools.
I have only ever seen one decent DIY/shop-made torque tester, and it appears to be well-calibrated for relative numbers.
Torque adapters are not an appropriate way to measure the max torque capabilities of cordless power tools.
Why is Any of this Important?
Let’s say you were to take out your cell phone and measure its length. What’s the value? How did you measure it?
Let’s say 10 other people have the same phone. What measurement did they get?
There are two types of data – qualitative and quantitative. Qualitative can be based on observations. Quantitative are based on measurements and numbers.
Would you measure the length of a phone in sugar cubes? Graham crackers? Not all sugar cubes and crackers are the same size.
Numbers need to be accurate and repeatable. This requires the proper tools and established techniques.
Repeatability has to be demonstrated.
What’s the point in taking measurements if the numbers aren’t reliable?
If a cordless drill is spec’ed at 600 in-lbs max torque, but tests at 400 in-lbs, are the specs inflated and bogus? That could be a big deal.
Or are the measurements inaccurate or otherwise flawed?
Maybe you can buy a torque adapter with 2% accuracy, lock one end in a vise, attach a drill, and get a reasonably close max torque measurement. Or it could be wildly off. Are the numbers trustworthy?
So What are the Options?
All that said, it seems that accurately checking the max torque specs of most 12V and 18V class cordless drills, and some 12V class and 18V class impact drivers can be done with one torque transducer. Modern brushless 18V class impact drivers will generally require a separate transducer. Mid-range and high-powered impact wrenches will require a heavy duty and appropriately-spec’ed setup.
It would take two setups for testing the max torque of most cordless drills, most impact drivers, cordless ratchets, and the least powerful compact impact wrenches. A third setup would be needed for the most powerful impact wrenches on the market. A fourth setup might be needed for greater accuracy when testing tools with lower max torque, such as 4V-class cordless drills, or the repeatability and torque stopping points of adjustable clutches.
The testing apparatus seems more important with reactionary tools, such as cordless drills, than impact drivers or wrenches. You can’t just hold the tool in-hand; drills under test should not be allowed to counter-rotate.
There are some multi-transducer testers, which shaves a little off the price by sharing a common display.
But there’s no escaping the need for multiple testing apparatus. There are 1/4″ hex to 1/2″ square drive adapters for testing lower powered impacts on mid-range transducers, but can we trust measurements if a stack of adapters are needed to adapt a 1/4″ hex impact driver to the 1″ drive (or larger) featured in higher torque range testers?
CDI’s electronic torque testers top out at 1000 in-lbs, or at least the product range that seems most suitable for testing cordless drills with a rundown adapter. They’re not rated for impact tools. It would run about $2400 plus the cost of adapters.
Joint simulators and rundown adapters are $400 to $700 depending on the brand, style, and size sometimes more. They’re available with different torque limits.
So to test say a tool spec’ed at 300 in-lbs, we’d want a rundown adapter of maybe 500 in-lbs. One that’s spec’ed to 1500 in-lbs might not allow for much rotation before the tool stalls.
Most tools are advertised with respect to their hard torque. Their soft torque is usually far lower, but provides a more useful comparative measure with respect to driving screws into wood and similar.
AWS’s smaller transducers are available in less and higher accurate varieties, and also display-less models. But they have a very long lead time.
The same brand’s impact transducers are very pricey and have ±1% full scale accuracy values, meaning that it would be hard to use just one to test the full range of 18V-class impact drivers and wrenches. These start at $4000, but don’t need additional rundown adapters. Not much information is available, but it looks like the rundown adapters are designed for hard joints. If they’re adjustable, it would be ideal to have a 250 ft lbs (3000 in-lb) transducer for testing impact drivers and a higher range for testing higher powered wrenches.
A 250 ft lbs model might suffice for impact drivers and compact impact wrenches. A 1000 ft lbs or higher model would be needed to test modern mid-size and higher-end models.
Impact wrench testers are pricey, but it’s not surprising; 1000 ft lbs exerts a lot of force for a transducer to hold up against.
It makes sense that a popular YouTube designed and built their own calibrated hydraulic ram-based tester.
Impact tools can quickly damage or degrade equipment not meant for the forces involved. It seems like a good way to ruin an expensive torque tester.
One brand says their torque specs are derived from 15 second test durations. 15 seconds of impact duration is going to require a heavy duty transducer and rundown adapter, and not just one that’s approved for impact testing. A quick calibration check wouldn’t be as hard on a torque tester, but doesn’t seem like the best way to test for max impact torque.
Narrowing Things Down
When looking into the different testing options now, I found a couple of more options previously unknown to me.
There’s no “do it all” test setup, however.
A torque tester that can handle all 12V and 18V-class cordless drills, cordless ratchets, and some impact drivers, plus 2 or 3 rundown adapters and joint simulators across the range, would be about $3500, maybe a little more depending on the brand or source of one of the adapters. Plus the cost of building a fixture around it. Computer cables and software are extra.
Two brands make heavy duty impact testers. One is limited to 180 ft-lbs (2160 in-lbs), the other has a wide range that goes well beyond the maximum torque that cordless 1/2″ impacts can deliver. These all start at $4000.
There’s a lighter duty impact tester that maxes out at around 362 ft-lbs.
Most of the lower-range torque testers I’ve seen are also around $2000 and up.
If a consumer wants to test numbers for themselves, why not use a $50 torque adapter with low accuracy. I’m not saying YOU need to go out and buy expensive testing equipment.
In order for ToolGuyd to publish numbers to satisfy the reader’s requests for independent torque testing, or in the pursuit of other torque-based insights, I must take every step to ensure the fidelity of the measurements.
For the data is to be trusted, the methods need to be sound and measurements need to be reproducible. The transducer needs to be designed for use with powered tools, and impact-rated if tested with impact tools.
Justifying the Investment
Give me two cordless drills, and I can quickly and inexpensively tell you which one can deliver a higher max torque. Qualitative testing is fairly easy.
Measurements that are accurate, repeatable, and as reproducible as possible, are not quick or inexpensive. Quantitative testing – the right way – is not easy.
Ideally, a one-tester-fits-all solution would be great, but that’s not happening. I’m also not spending what it would take to test tools across the entire practical torque spectrum.
There are some DIY or homebrew options, but I have enough projects. A turnkey solution that I could just use with high confidence would be nice. I’ll keep looking into it.
Will it be worth it? In my opinion, no, at least not just for the sake of measurements. A couple of thousands of dollars worth of equipment, just to verify technical specs that aren’t the most useful anyway? But if it’s something readers want to see, I can find other ways to use use the same equipment.
How repeatable are torque clutches? Can we test the differences in mechanical and electronic clutches in this regard? How might adjustable torque clutch characteristics change for different brands or models?
A cordless power tool brand recently updated their 12V-class impacts, and on top of the well-advertised updates, they changed how the trigger switch is tuned to control output speed. Rather than a mostly linear relationship between trigger switch travel and “percentage of total power,” the output is a lot flatter from 10 to 50% than with the previous model. They redesigned the trigger switch to give a lot more speed and torque control in the mid-range. This is something that would be very hard to show without measurement-based testing. That kind of data is interesting to me, especially because it’s not something tool brands will readily share.
Five plus years ago, tool brands were still racing to one-up each other with respect to torque and power. Now, we’re starting to see more differences “under the hood.”
If such data is to be collected with any reproducibility, misusing a consumer torque adapter with low accuracy is out of the question.
So that’s why I’m looking into this again. The reader request suggested there’s interest in measurements, and I am interested in comparing max torque against advertising claims and different brands’ models. And, there are even more things we can look at. Most of the equipment I’ve looked at so far, except for the impact-only ones, can also be used to check the calibration of manual torque wrenches and the like as well – within their measurement ranges – which would also be useful.
I’m not about to invest 10 grand or more in a suite of torque testers, but I can budget for a tester that might handle a majority of what I’m looking to do with cordless drills.
I can justify some investment in test equipment, just not as much as it would take to test every type of drill and impact tool 1/2″ driver and under – at least not all at once. A prudent approach would be to start with a torque tester that can test as broad a range of tools as possible, and to see how things go from there. When I run out of things to test, maybe then I can look at additional investments.
All of this is partially to clear my head, and mostly because a couple of regulars mentioned in the past that they liked seeing my behind-the-curtain thinking about things like this. Whatever setup I land on, a lot of what was discussed here will have went into the decision-making process.