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Master of Technology

cube inside cube
In this article we will introduce you to the technology of manufacturing geometric metal solids, which are used by master Ivan Kochkin.

The technology of making one geometric body inside another is very exciting. And the more pieces there are in one, the more difficult it is to make them.
The master managed to learn how to create bodies that have seven levels. That is, six others are machined inside one shape.
Here are some examples of work:
On the attached photos - cubes with a side of 50mm, divided and undivided:

six cubes inside

Dodecahedrons inside a 31mm ball (4 levels):

dodecahedrons inside a cube

Dodecahedrons inside a 50mm diameter ball (6 levels):

dodecahedrons inside the ball

Dodecahedrons inside a 63mm diameter ball (7 levels):

dodecahedrons inside the ball

Another nut is machined inside the nut:

nut inside the nut

I started making cubes and balls, says Ivan, 10 years ago on a manual machine. It really was hard work, it took about 2 hours of work to the brink of a cube. The cube has 6 faces, the total processing time was about 12 hours. With a polyhedron in a ball is still more difficult - there are already 12 faces at the dodecahedron, and 20 - at the icosahedron. Working a couple of hours a day in the garage in the evenings, it took up to a week of work for dodecahedrons in a ball. Mistake due to fatigue, for example, led to marriage. And it all started over again!


The ball blank is fixed in a special chuck of the machine with manual control.


So I built a CNC lathe that unloads from the routine and reduces the chance of human error. However, the machine does not forgive errors in the program, in the processing modes, or poor fixation of the NC workpiece:

marriage making a cube cubed


The main stages of building a CNC lathe can be found on the Internet.

But the machine is not everything. We need a product model, a technological chain, a program for the machine, a tooling that allows you to fix the workpiece and orient the part to process the next facet with an acceptable error, a non-standard cutting tool.

Photos of my machine with a set of tools needed to make a cube in a cube. I use three tools, the nest of the 4th tool is unused.
The cube blank can be clamped in a split bushing (as in the photo), or in a four-jaw chuck:



After machining, the removal of internal burrs from all faces, cleaning, polishing of internal parts that are difficult to reach. A master who spent a week of his time making a unique specimen on a manual machine can spend another couple of hours “shining in”. When using a CNC machine, it is manual operations that take too much time and, if possible, are subject to automation. The technology comes to the first place - a step-by-step process, which allows to get a satisfactory result in the minimum time with the minimum number of operations.

The steps of making a dodecahedron in a ball:

dimensions of the dodecahedron inside the ball

The ball blank is machined from a bar on a CNC machine. In the video - turning the hemisphere. Then the hemisphere is inverted, fixed in a holder with a spherical counter surface, and the second half of the ball is processed. It takes 3-5 minutes of machine time to grind out a hemisphere, depending on the size of the ball.

Then, 12 pilot holes are manually laid out and drilled, according to the number of faces of the dodecahedron.

Then again comes the turn of the CNC machine, with which 11 faces out of 12 are sequentially processed. One face is processed for 3-10 minutes, depending on the volume and complexity of the work.

An example of processing one side. This video shows the turning of the “nut in the nut” - a simpler figure. Therefore, the processing time of one facet is only one and a half minutes.


Before processing the last facet, the future polyhedra must be securely fixed inside the part so that, after their separation, they will not unpredictably rotate inside, destroying themselves and breaking the tool. Some masters pour the inside of the ball with melted sealing wax, rosin, hot melt. I, like many others, use melted paraffin.

After paraffin has stiffened, and has been cooled in the refrigerator, it is possible to process the last edge. This face sharpens with gentle turning conditions, since the mechanical strength of the paraffin gluing the internal surfaces is small. Accordingly, this face takes 5-15 minutes to process. Then the balloon is heated with hot air from a building dryer to remove paraffin, and washed in a solvent.

Mechanical cleaning and deburring occurs in a rotating drum, like in a washing machine, only without water. Balls are rolled inside, all internal figures experience multiple collisions, which remove sticky chips and burrs. The processing time in the first drum is from 15 to 45 minutes, depending on the material (brass, for example, requires less processing time), and the size of the figure. The process goes on without human intervention; at the same time, 4-5 details are processed.

Then finer cleaning and light polishing in the second drum with a dry polishing powder is carried out. This stage requires 30 minutes - 1 hour of time. 2-3 parts are processed simultaneously. If you put more parts at the same time, they can scratch each other. You can use a large drum into which you will need to load more powder.

The final operation - polishing the surface of the ball. It is made by hand on a felt wheel with GOI paste. Then - washing in gasoline and hot water with soap.

Total, for the manufacture of a large 63mm ball with six dodecahedrons inside, it can take about 3 hours of my time - this does not include processing in the drums. But there my participation is kept to a minimum.
And to manufacture, for example, a cube with a side of 25mm, it takes about 45 minutes. Nuts are also made quickly.

In the process of processing the item is losing weight. For example, an aluminum ball with a diameter of 63mm with six dodecahedrons inside weighs 37 grams, only 7% of the weight of the workpiece. And 93% of the mass of the material goes to waste!

dimensions of the dodecahedron inside the ball

Wood processing requires other cutting modes - cutting speed and material removal. For machining wooden parts, I use a high-speed spindle as a tool. The video is processed cube maple wood size 72mm.

Article, photo and video materials provided by the author - Ivan Kochkin (gone4beer@mail.ru)

© polyhedr.com  02/05/2019


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