Milwaukee claims that their Stud Gen II tape measure can survive an 80′ drop.
Dewalt claims that their new Tough Series tape measures is rated to still work after a 100′ drop.
Both brands make their claims with respect to packed soil, which complicated things a little bit. Does Milwaukee’s “packed soil” have more clay and rock contents, and Dewalt’s more organic materials? Or do they use an engineered fill according to professional standards?
Unless both brands are testing their tape measures by dropping them off the tops of buildings or cranes why are they using packed soil as an impact surface?
The drop surface is important because it can influence impact force. Would you rather jump barefoot in soil (packed or not), or concrete? Soil is a softer, deformable, and energy absorbing surface. But I digress – more about this in a bit.
In yesterday’s post about the Tough Series tapes, Tom D made a good point:
I’m kinda worried where someone could be that a tape could have a 100’ drop without being tied off – hope those down below are hard hatting!
There are two ways to interpret the drop rating claims – you can take them literally, or you can translate it into comparative impact resistance.
It’s common to drop a tape measure off a ladder, but is anyone really dropping their tape measures from 80 feet or 100 feet up? They really shouldn’t be. At heights, safety tethers should be used to avoid injury to anyone who could be working below.
Let’s talk about energy.
Ignoring the impact surface, we’re only going to look at the energy of a falling tape measure.
For a falling object that starts motionless at x-height, the speed is:
a is the acceleration due to gravity, 9.8 m/s² (or 32.17 ft/s²). You can learn more via HyperPhysics.
So for tape measures being dropped from height, the impact speed is:
- 71.7 ft/s from 80′
- 80.2 ft/s from 100′
Kinetic energy, the energy of an object in motion, is:
For simplicity’s sake, let’s say the two tape measures weigh the same. I’ll use 0.5 kg (1.10 lbs) as a ballpark estimate.
Kinetic energy just before impact:
- 119 Joules for either tape dropped from 80′
- 149 Joules for either tape dropped from 100′
For perspective 119 Joules is about the same impact energy as dropping a 44 pound steel weight from a height of 2 feet, and 149 Joules is about the same impact energy as dropping a 55 pound steel weight from the same height.
(Please feel free to check or correct my math!)
Or, just before impact, with m being the mass (in kg), g being the acceleration due to gravity (9.8 m/s²), and h being the drop height.
So, if a tape measure can survive a 100′ foot drop and still work, it can in theory endure a 55 pound weight being dropped on it from a height of 2 feet. If a tape can survive a drop from 80′, it can in theory endure the impact of a 44 pound weight dropped from 2 feet.
If the impact resistance claims are perfectly accurate, the orientation of the tape measure – front, side, top, etc. – shouldn’t matter.
I’m not sure how the packed soil impact surface changes things. Let’s say you have a tape measure on concrete and drop a heavy weight on it. It’s going to absorb much more energy from the impact than if it was placed on packed soil where it could potentially help to dissipate some of the impact energy.
Think of it this way – you place one glass marble on concrete, and one on packed soil. Now drop a brick on it. On concrete, the glass marble might crack or even shatter. On packed soil, might the marble indent or even become embedded in the surface?
How does all this translate to real-world drops? It doesn’t!
Tape measures rated to 80′ or 100′ should both be able to survive drops from a stepladder, your truck bed, your benchtop, or other common work heights.
Things get really complicated without context.
Which tape measure weighs more? Due to the constant acceleration of gravity that’s independent of mass, any two tape measures dropped from the same height will have the same impact velocity, barring any aerodynamic differences at extreme heights and speeds.
But, with energy being mass-dependent, that factors into impact energy.
Let’s say that Dewalt’s tape measure is lighter than Milwaukee’s. Well, different drop height ratings can potentially be misleading. Basically, it’s possible for a heavier tape measure with a lower drop height rating to endure harder impacts than a lighter tape measure with a higher drop height rating.
How many high impact drops can a tape measure endure? Are brands testing them to x-number of drops?
All this isn’t to say that drop rating are meaningless, because they’re not, they’re just very hard to interpret.
As far as I can tell, both brands’ drop ratings don’t seem to adhere to any disclosed standards.
Flashlights, on the other hand, have published drop rating standards. ANSI FL1 standards, for example, require that a flashlight be dropped from the rated height (of at least 1m) onto cured concrete (6) times from different cubic-face orientations, and the products must remain fully functional without any visible cracks or breaks.
Brands that advertise flashlights according to ANSI FL1 standards are ideally using comparable test methods, and their test results should be repeatable by competitors, users, or really anyone.
I would guess that brands use drop weight towers to simulate drop impact energy, but it’s unclear how that might translate to “packed soil” drop height ratings. Without official standards – at least those that are openly disclosed and described – it’s impossible to really compare different brands’ drop ratings against each other.
Most brands test competing products, keeping each other in check from making false claims, but the seeming absence of known test conditions means you can’t take competing claims to be directly compatible.
Will Dewalt’s new Tough Series tape measure be more durable than Milwaukee’s? Can it endure harder impacts? Will Milwaukee have to drop their claims of making the industry’s most durable tape measure? Maybe, maybe not.
The point I’m trying to make is that a drop height rating is a very imperfect comparative measure unless greater context and details are known. The maximum impact energy from any orientation is the important comparative factor, and I doubt we’re going to get that from either brand.
Long story short, both brands’ tape measures are extremely tough. The question of which is stronger, tougher, or more durable isn’t one that can be answered with a drop height rating.