Long handled club
For some time I have wanted a long handled club. My intention was to do gada swings, grave diggers, barbarian squats, and dynamic curls with this club. It would be about 1.35 metres in length, and weigh about 9 kg. Here is a diagram of what I had in mind:
So I was overjoyed when I found a suitable piece of wood to make my club. It is a grey ironbark branch that had broken off the trunk, due to some illness. The local municipality workers had cut it into short lengths, and left it where it had fallen.
Grey Ironwood (Eucalyptus Paniculata) is extremely hard and difficult to work when it is dry. My strategy is to do the shaping while the wood is wet. A test cube shows that the wet timber has a density of 1.20. After drying in the microwave oven, it has a density of 1.04. If I want a dry weight of 9 kg, then the target weight for the club before drying is 10.38 kg.
I removed the bark from a 1.5m section, and brought it home. At this stage, the log weighed 55 kg.
The piece of wood was simply too big and too heavy to mount in my bench vice, so I did the trimming with the log on my garage floor. The trimming was done with a bow saw and a chisel.
I used a plane to smooth the rough faces, and make them square. The piece of wood now weighed 25 kg, and it was small enough to mount in my vice. (In case you wondered about the knife - it was used for sharpening my pencil!)
I shaped the handle, and removed more wood from the body of the club. Weight is now 19 kg.
The body of the club has been planed into a truncated octagonal pyramid. It now weighs 12.7 kg.
The octagonal pyramid was planed further to produce the conical shape above. The weight is 10.9 kg. Still a few hundred grams to go.
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The top and the base of the cone have been rounded, and the button on the end of the handle has been shaped. The club weighs 10.6 kg. I will let it dry to equilibrium weight, (might take a year to get there!) and then I will do the final adjustments.
I brought the log home on the 23rd March 2015. Shaping was complete on the 5th April 2015. Altogether about 50 hours of work stretched over 14 days.
I brought the log home on the 23rd March 2015. Shaping was complete on the 5th April 2015. Altogether about 50 hours of work stretched over 14 days.
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Update 7 July 2015. The resin in my refrigerator was getting progressively thicker, and I had to use it before it gelled. So even though the club had not dried to equilibrium weight, I had to finish it. The graph below shows how the weight was dropping steadily, but hadn't bottomed out yet.
I filled the cracks with epoxy resin, and filed and sanded the club. I gave it one coat of the resin I use as a varnish. The club now weighs 9.3 kg.
I made a short video to demonstrate the exercises I will be doing with this club. I made the video before the club was finished.
In case anybody is interested: The gravedigger is a superb all around exercise. It is the club swinging equivalent of that old Olympic standard, the clean and press!
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And now for a little bit of science. Before making my long handled club, I made a mace out of a length of hollow steel tubing and a few cast iron weights. I wanted to establish how heavy I should make the club for the exercises I intended doing. I was surprised (and a little disappointed) to discover that they had very different swinging properties. Even though they weighed the same, and had their centre of mass at the same distance from the hands, the steel mace swung faster, and did not lead to painful elbows. I thought my club would behave like the illustration in (B), i.e. a point mass of 9 kg located at a distance of 95 cm from the hands. Instead, it behaves like the illustration in (C), consisting of two point masses of 4.5 kg. The centre of mass is still 95 cm from the hands. But instead of behaving exclusively like a pendulum, it behaves like a pendulum/flywheel combination.
In a pure pendulum, the gravitational potential energy is converted to kinetic energy on the downswing. This kinetic energy is converted back to potential energy on the upswing. Barring for small losses due to friction, all of the kinetic energy is converted back to potential energy, and a mace or gada returns approximately to the same position it started from.
The situation is different in the long handled club. Some of the potential energy is converted to translational motion, and some is converted to rotational motion (i.e. the body of the club rotates about its centre of mass). So the potential energy is stored as both linear as well as angular momentum. The immediate result of this is that the club does not return to its original height. That is the cause of the sore elbows - you need to muscle the club back to its original position. Once I figured this out, it was a small matter to push the club higher before initiating the downswing. No more sore elbows!
In a pure pendulum, the gravitational potential energy is converted to kinetic energy on the downswing. This kinetic energy is converted back to potential energy on the upswing. Barring for small losses due to friction, all of the kinetic energy is converted back to potential energy, and a mace or gada returns approximately to the same position it started from.
The situation is different in the long handled club. Some of the potential energy is converted to translational motion, and some is converted to rotational motion (i.e. the body of the club rotates about its centre of mass). So the potential energy is stored as both linear as well as angular momentum. The immediate result of this is that the club does not return to its original height. That is the cause of the sore elbows - you need to muscle the club back to its original position. Once I figured this out, it was a small matter to push the club higher before initiating the downswing. No more sore elbows!
I realize after doing the calculation that the effect is not as great as I thought. 5.7 joules out of a total of 176 joules is stored as rotational energy. This equates to a loss of height of about 8 cm on a typical gada swing.
According to Galileo, all objects fall at the same speed under the influence of gravity. This is true of freely falling objects, but is not true of constrained objects, like clubs and gada's. Here is a wonderful illustration showing the effects of moment of inertia on the speed of objects rolling under gravity. http://en.wikipedia.org/wiki/File:Rolling_Racers_-_Moment_of_inertia.gif The hollow sphere (red) and hoop (green) store a greater fraction of the gravitational energy as rotational energy, and this slows them down.
According to Galileo, all objects fall at the same speed under the influence of gravity. This is true of freely falling objects, but is not true of constrained objects, like clubs and gada's. Here is a wonderful illustration showing the effects of moment of inertia on the speed of objects rolling under gravity. http://en.wikipedia.org/wiki/File:Rolling_Racers_-_Moment_of_inertia.gif The hollow sphere (red) and hoop (green) store a greater fraction of the gravitational energy as rotational energy, and this slows them down.