I can’t tell you what started it, but I am utterly fixated on hammer theory today.
Titanium hammers have always been in a special grey area, where manufacturer’s claims have always seemed a bit boastful.
And then, in 2011, Dewalt kicked off a new “weight of titanium, strength of steel” hammer that many other brands raced to match.
Dewalt’s explanation really bugged me at the time – I remember biting my tongue at the press luncheon – and continues to bug me even now.
How does Dewalt’s MIG-welded hammer (15 oz) work to provide “the feel of titanium at a fraction of the cost” while also delivering “the power of a 28oz framing hammer?”
They said something along the lines of:
Kinetic energy = 1/2 x mass x velocity ^2. So even though we lightened the weight of the hammer, users can swing it faster to deliver greater energy. Our 15 oz hammer swings like a 28 oz hammer! Weight of titanium, strength of steel!
No, no, no.
In my opinion, this was complete BS. Why are we talking about kinetic energy here? Is this what Dewalt and Stanley Black & Decker engineers believe, or is this just a way to throw some science talk at journalists that might have taken it at face value?
What happens when you swing a hammer faster? Yes, it hits harder. Does the nail heat up more due to frictional losses? Does it make a louder sound upon impact? Does it rebound more? These are all energy losses, with some directly related to strike velocity.
Momentum is what we really need to talk about. Simplifying things, linear momentum is directly proportional to mass and velocity; p = mv. So now, you decrease the weight of the hammer head and you must increase the velocity of the swing in order to match heavier hammer momentum to hit just as hard.
Again, simplifying things, if you drop head weight from 28 oz to 15 oz and consider the handle to be massless, you have to swing the hammer nearly twice as fast to deliver the same nail-driving momentum.
This is why I really didn’t like the “velocity is squared, and so speed contributes more significantly to hammer energy than mass” suggested marketing claims.
There are a lot of things going on.
Let’s use Stiletto’s titanium hammer for break-down purposes.
Titanium hammer handles generally offer better vibration-dampening properties than other materials, such as wood and steel. But let’s ignore that for a moment.
What contributes to hammer striking speed?
- Head weight
- Handle weight
- Handle length
The heavier the hammer head, the greater the swing effort.
The heavier the handle weight, the greater the swing effort.
The longer the handle, the greater the swing effort and faster the head swing.
For the best hammer design, you want as light a handle as possible, without compromising speed or durability.
The handle weight is the least-valuable contribution to a hammer swing. At this time I would also say that these are all just my opinions, and that I am open to discussing corrections or alternate theories.
Consider the Stiletto titanium hammers, Dewalt’s MIG-welded hammer, or any of the higher performance hammers released in recent years.
The focus has been on light and slender handles, with weight-savings up to the very top of the hammer head.
The moment of inertia can be summed up as the effort required for a hammer to be swung at a desired striking speed. In other words, the greater the moment of inertia, the more effort required to swing the hammer.
For a point mass, or the hammer head, the moment of inertia is mr^2.
For a rod of length L and mass m rotated about one end, or the hammer handle, the moment of inertia is 1/3mL^2.
So, when you swing the hammer, the weight of the hammer head and handle resist your swinging motion, lending to fatigue. While the weight of the handle does contribute to the swing speed as well, it’s less significant than the weight of the hammer head.
Look again at the Stiletto T-bone handle design. You have an I-beam shape and also two cut-outs where material – and weight – is removed.
For a harder-hitting hammer, you also want to tune the hammer head weight and also the length of the swing arc.
Consider two wheels, on with a 12″ diameter, and one with a 16″ diameter. Which wheel covers the greater distance in one rotation? Now, roll each wheel with the same angular speed, meaning you roll them at the same rotations per minute. Which wheel has the greater linear velocity?
Take two hammers, one with a 12″ handle and the other with a 16″ handle. If you swing them at the same angular speed, the longer-handled hammer will have a great linear velocity at the hammer head.
Ignoring hammer head or handle weight considerations, a longer hammer will swing faster than a shorter hammer. The angular rotation might be the same, but the swing arc length depends on the swing radius.
Stick out your hand and make a “thumbs-up” gesture. Now, keeping your joints straight, take one second to bring your thumb back down and close your fist. Your middle knuckle closes the distance at a rate of what, maybe 1-inch per second? What about your fingertip? 2-inches per second?
Ignoring most other factors, a longer hammer hits faster and thus harder.
This is also why you can reduce the hammer weight.
If you reduce handle weight, you can reduce swing effort. This means that you can achieve the same velocity with less effort, or greater swing velocity with the same effort.
Lengthen the hammer, and you increase hammer head swing velocity. If you can reduce the handle weight along the handle or at critical locations in the hammer head, you can lengthen the hammer without increasing swing effort.
If you fine-tune everything with a balanced design, you can even reduce the hammer head weight to achieve “feels like a 28oz framing hammer” types of marketing claims.
Many other factors go into hammer design, such as vibration dampening properties, and having enough mass behind the claw to provide sufficient strength for nail removal or prying tasks.
When Dewalt’s product managers first talked-up their MIG-welded framing hammers, the “you can reduce mass because kinetic energy relies on velocity squared” really struck a nerve, and it has continued to bug me since then. But on a positive note, it got me thinking about what happens when you start changing a hammer’s physical properties.
I could of course be wrong.
Let me know in comments about your hammer preferences and what you’ve learned over the years.