Hammer bounce

This is pretty counterintuitive. I had a three-pound Estwing
drilling hammer. My favorite hammer. The task was to knock all forty
wheel studs out of the back end of a tractor. Then hammer in longer
ones. Brand new vehicle, so no rust.
Anyway, got a little tired after the first one, decided to use a
larger hammer. The guy I was working with had a five-pound minisledge
with a wood handle. I borrowed it and nearly knocked myself out cold.
Where it took my little hammer three to five hard hits on average to
remove a stud, it took his five-pound hammer five to ten swings, and it
clearly bounced a great deal further back each time. Whether it was
him, me, right hand, left hand, one hand, two hand, results were pretty
So how in the hell is it that a bigger hammer bounces back harder and
drives the stud less?
I'm mad about that, even if my hammer turned out to be better.
Damned head still hurts.
Reply to
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In article , "B.B." wrote:
Larger hammer means it was traveling slower. A smaller faster hammer can deliver more energy per hit. Driving out wheel studs requires the sharp fast crack of a smaller hammer.
Reply to
Ernie Leimkuhler
beyond that.... not all hammers are created equal. there are great variations in head design, metalurgy, heat treating and sometimes hardfacing. getting the right taper in the handle and correct handle material makes a huge difference. Im not that keen on many of the more modern super handle materials, but from experience.... the right kind of wood and right taper make a difference like night and day. some small sledges almost perform like lead shot hammers.
Reply to
Shaun Van Poecke
On Mon, 19 Feb 2007 23:33:53 -0600, with neither quill nor qualm, "B.B." quickly quoth:
You could surely get a better velocity with the smaller hammer. You can't swing as quickly with a heavier, bulkier sledge. Also, the big sledge might have had a harder face, too.
But why on Earth didn't you take out an air hose and use an air hammer on it, Bubba? I've even used my CP [That's a real Chicago Pneumatic longnosed (CP703, I believe) air hammer which can really HIT, not a little HF gun] on air tanks. It took two 5gal tankfuls to remove the pitman steering arm from my F-150 with a pitman pickle fork. For serious jobs like that, use air! It would have taken you ten minutes, max. (And a helluva lot less sweat.) That's if you didn't have a press to do the job.
P.S: Did you bend an axle? Why all new studs?
-- This would be the best of all possible worlds, if there were no religion in it. - John Adams
Reply to
Larry Jaques
My experience (for floor-laying) is the reverse. I use a (metal) mallet, because it bounces less. I think it drives more than it slams.
Don't ask me for a physical explanation. Seems to depend on several factors which hammer is better.
BTW bouncing hammers: For hammering down work in a vise, I use a lead filled (with little balls) hammer with nylon tips. He bounces the least. But for some parts, that insist on bouncing, I have to use the smaller or bigger model. :-))
YMMV! Never use force, just go for a bigger (or is that different?) hammer!
Reply to
Nick Mueller
In article , "B.B." wrote:
If the mass of the hammer head more or less matches the effective mass of whatever one is hitting, the momentum transfer will be more or less perfect. When perfect transfer occurs, the hammerhead stops dead, and the target takes off at the same speed as the hammer head arrived at.
This can be shown by shooting coins into one another on a smooth tabletop. It the two coins are the same, the moving one stops dead and the stationary one takes off. If the moving one is heavier, it slows down a bit but keeps on going, while the stationary one starts moving, all in the direction of original travel. If the moving one is lighter, it bounces backwards even as it starts the stationary one moving in the same direction as the incoming coin had been moving.
So, why did a heavier hammer come back and bonk you? Because instead of stopping dead (masses matched), it kept on going, compressed the springiness of whatever held the target up, which then proceeded to uncompress and throw the hammerhead back at you. With glee.
Joe Gwinn
Reply to
Joseph Gwinn
The other replies are confusing momentum and energy. Getting the bolt to move requires enough minimum energy to break the friction bond. Until you get sufficient energy the bolt doesn't move at all. If it doesn't move, the energy of the blow just compresses the bolt, it springs back and bounces the hammer. It could peen the end over and use some energy that way but looks like in your case no. Momentum just tries to move the tractor over, you'd never see it.
Energy is mv^2 so if you can swing the Eastwing 30% faster than the mini sledge, you are even up. I'm really fond of Eastwing hammers, they are truely nice to hold and use. I'd guess you are getting a much better swing, cocking your wrist to get the extra snap. Probably something like double the speed and more than double the energy.
B.B. wrote:
Reply to
Interesting question. I think the answer depends on the lug in the wheel and the lug swinging the hammer as well as the hammer itself.
Hammer energy at moment of impact is 1/2 M * V^2, M being hammer mass and V being it's velocity. The energy it delivers before it stops is integral (F(x) dx) In an elastic collision F(x) is proportional to X so energy = 1/2 (Fpk)^2 where Fpk is the peak force. In a perfectly elastic collision where the struck object (lug stuck in tractor wheel) stays put, all of this energy is returned to the hammer -- it bounces. If a peak force is reached that causes the lug to move (desired effect) then much of the energy is dissipated in moving the lug so the hammer bounces less if at all. The key is that a minimum peak force must be reached to make the lug move at all.
Integrating and rearranging, Fpk = Vpk * sqrt(E*M) where E is the modulus of elasticity. This says that peak force varies directly with hammer velocity and as the square root of hammer mass. That's where the lug swinging the hammer comes in. When you reach a point where increasing weight by factor u decreases your peak velocity by sqrt(u), you start losing ground. You and I can each swing a small ball peen about as fast as a tackhammer, but we each eventually reach a point where increasing the weight appreciably slows our swing. Lugzilla can swing a heavier hammer before he starts losing peak velocity. We can all hit harder with a longer swing because we can accelerate the hammer head more during a longer swing thru a greater distance. The hooker there is getting the energy delivered where it's needed; missing the lug altogether does not produce the desired effect!
A heavy hammer is good for driving a mass that must move appreciably and will start moving at lower peak force, e.g. a chisel, drift or large nail. Then momentum must be imparted to the driven object, momemtum varies directly with velocity rather than as V^2 so you can swing a heavier hammer before you start losing ground.
Reply to
Don Foreman
I have one of those: Little, short-handled "hand sledge" for star drilling. All things be told, I've used it for most sledge hammer work, up to and including "encouraging" studs and posts into alignment and driving stakes. I still have an old 10 lb. maul I use for heavy stake driving -- but I, too, love that little Estwing.
I believe part of the reason you can develop _much_ more velocity (more than just 30%) with the 3lb Estwing over a 5lb hand sledge is because of the short handle. With more mechanical advantage over the head, the 'average' wrist can give it a better sling than with a longer handle.
This is why small or weak people tend to choke up on a claw hammer. The requisite wrist snap is intuitive, and you can't get it without enough advantage over the head.
Reply to
Lloyd E. Sponenburgh
How was the axle supported? Was it in the tractor, sitting against some surface, or whatever?
I wonder if hammer hit stud, axle moved against something that didn't give, rebounded and sent energy back at hammer that had just transfered momentum.
Reply to
I was working in someone else's shop, so I only had a handful of tools. Normally I do use the air hammer to knock 'em out. It's Matco's off-brand redline hammer with the long barrel. It can shove a straight punch through a frame rail if given enough time. I love it. But there's no room on the back side of the hub to buzz the new studs in, so I'd have to use a little hammer anyway. They got a truck with all steel rimmed wheels, and they wanted to change over to aluminum rims. Since the aluminum rims are quite a lot thicker, we needed to change the studs out in the rear. The fronts were long enough. Barely.
Reply to
If you can get a pc of heavy pipe that clears the bolt head on the back side of the axle ,as a back up mass, you will get much more force transmitted to the bolt....The axle flange is "springing"--that's whats bouncing your hammer back..
Reply to
Jerry Wass
On Wed, 21 Feb 2007 09:26:16 -0600, with neither quill nor qualm, "B.B." quickly quoth:
I always used my 1/2" impact to draw new studs in with 2 thin flat washers on the front and lugnuts flipped backwards to let 'em pull better. Final tightening and alignment comes with torquing the wheel on.
Don't wheel mfgrs normally include longer lugnuts for thicker rims like they used to?!?
BTW, when you said "tractor" I thought John Deere, not Peterbilt.
-- If it weren't for jumping to conclusions, some of us wouldn't get any exercise.
Reply to
Larry Jaques
I've done that before, but there's always a risk of a metal shaving jumping out of the stud hole into the nut and chewing up the threads, so these days I just beat studs in rather than deal with the hassle of getting more. Our parts department is absolutely terrible and hell to deal with, plus the paperwork bullshit of getting more parts than absolutely necessary.
Yeah. Disc-wheel tandems can be set up as either steel-steel, steel-aluminum, or aluminum-aluminum. The first is the strongest and cheapest, but also heaviest, the last one is the lightest, but weakest and most expensive, and the middle one is a good compromise that looks snazzy. Most of the trucks have either the steel-steel or steel-aluminum setup, and the default studs are long enough for either. But going to aluminum-aluminum is just too long for the studs, so you need longer ones at that point. These days you can get "supersingles" in the rear, which is just one extra-wide tire. Very expensive, but shaves off around 100 pounds per wheel end. Trucks speced out with those have SHORT studs in the back.
Reply to
Use a ten pound long handled sledge like you use to drive railroad spikes and fence posts. I doubt that would bounce and would really have some energy with a full swing
Reply to
daniel peterman

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