Microscopic preparation of amber


Basically, any device with relatively stable rotation of the polishing disk is suitable for processing the small samples. There also should be some way to moisture the surface of the disk to protect a sample from overheating. An easy change the polishing disks of different grain size is also desirable.

USB-powered polishing machine

We designed a portable polishing machine which can be powered from the standard computer USB port. It is compact and its polishing disks are easy to change. Now we utilize the third generation of this device, which was optimized for easier operation and disk stability. Under the name of MiniPolly it is commercially available from OpenScience.

Polishing machine from a floppy drive

As a source of rotation we used a standard computer 3.5" floppy drive. Apparently, the model and make of a given drive are not important since we made several devices using different floppy drives. Older models, however, usually had better quality of mechanics, but newer were more light-weighted. Sure enough, a specialized motor with more convenient mode of operation may be used for the purpose. Floppy drive motor is good only in the following respects: 1) it is cheap and easy to get (at least it was so in Moscow of 2012–14, when and where we designed our device), 2) it has a suitable rotation speed, 3) usually its spindle is fixed in its chassis with a bearing and 4) majority of the floppy drives can be powered with +5V from a standard USB port.

From a floppy drive, we have only taken the part of the chassis with the motor and its control circuit board (usually the latter is separate from the rest of the drive's electronics, but the part of the chassis had to be cut away). With applying the +5V voltage and grounding some of the main chip's control lines, it is possible to start the rotation of the motor. Most floppy drives allow to set at least two rotating speeds. Although the trial and error method is quite effective here, we recommend to use the datasheet for a given chip.

It is important to protect the internals of the device from water coming from the polishing disk. Photo shows an example of our polishing machine wherein we did not pay enough attention to this, and the traces of corrosion are visible on metal parts. However, this very device still functions normally.

We also made a more powerful version of a polishing machine based on a 5.25 floppy drive. The principle of motor control is similar, except it requires dual voltage (+5V, +12V). The whole device is substantially larger and heavier and requires more workspace, so in the end we preferred the more compact version.

In our polishing machine the electronic part of the floppy drive is packed into the CNC milled plastic case together with a on/off switch and a Mini-USB socket. Silicone rubber feet are added on the bottom for stability.

Flat rotating disk of a floppy drive motor is facing up. Instead one can use its spindle by attaching details directly to it; this can provide higher precision of rotation. We glued to the motor a CNC-milled rectangular plastic part with a powerful magnet inserted in its center. It was designed to fit the bottom of a plastic polishing disk. This rotating part projects from the case through the hole in its top. The rim around the hole serves to hold a plastic container or a bowl which collects water coming from the polishing disk.

Polishing disks are milled from acrylic (plexiglas). Each has a rectangular socket in the center of its bottom surface to fit the shape of rotating part, and a cirular groove that fits to the rim around the hole in the cover to prevent water from coming inside the device. Each disk is equipped with a magnet. Top surface of a polishing disk is flat and smooth, and a sheet of a waterproof sandpaper is glued onto it.

Later we switched to using a plastic disk with a layer of magnetic vinyl glued to its surface. This single disk can replace the whole set, provided that different abrasives are glued to the layer of a flexible magnetic receptive material and cut to the shape of a disk. Stability of the polishing surface, though, is a bit compromised, especially if some particles interfere between the disk and the 'magnetized' sandpaper.

To collect water, which is being fed to the disk during the polishing, a suitable-sized plastic container is used. A circular hole is cut in its bottom such that it sits tightly on the rim around the rotating part of the device.