[G03-P02] Recipe 2.0 for rock thin-section study in a classroom. Part 2. Making
Keywords:Thin-section making, Rock saw, grinding machine, geoscience club
In a classroom, for the sufficient study of thin-sections, we have to prepare many samples. However, they are very high expensive, around 20 USD for each thin-section, so we can not purchase enough samples. For this reason, we tried to make home-made tools for the thin section making. Instead of the use of high-cost rock saws or rock-grinders, we try to use inexpensive mass production machines for the base of our system. Easy-making additional tools can complete cheap alternative tools. A table-top bench grinder and a rotary kitchen sharpener are chosen. They can be purchased from a DIY store less than 100USD for each.
In our trial, for the rock saw, we use a 150mm twin bench grinder as a base machine, and one side of the grindstone is removed, including its cover. A water tank with a table made from acrylic plates is fixed to the base of the motor with bolts. For the rock sawing, a cheap diamond blade (160mm to 180mm diameter, 1mm thickness) is mounted on the motor shaft with arbors, which is made using a table-top lathe machine. Except for this lathe operation, most of the processes can be completed with usual electric tools. For the cutting of acrylic plates, we use a hand cutter and glue specialized for acrylic work. On the water tank, an aluminum 3mm thickness board, having a slit for the blade, is fixed as a saw table. Also, at the bottom of the tank, a draincock was drilled.
The rock sawing is carried out with a quarter filled water. For safety, we have to set the ground for the electric system. A 1mm thick diamond blade is useful for the generic rock sawing. We can smoothly cut around the fist-sized rock with enough motor torque. When we cut the glued rock sample attached to the slide-glass, we set a guide for thin rock sawing on the table using a cramped acrylic block. After some training, we can cut the section within 0.5mm thickness. For the rock and glass gluing, a 90-minute hardening "Bond-E" is used. Also, we use a hot-plate for rock warming to make glue more liquidity.
Next is rock grinding. Hand grinding is the primary way of traditional method; however, we use a new grinding machine based on a kitchen knife sharpener, which consists of a rounded wet stone, a water tank, and a motor. A diamond grinding disk, 180mm diameter and 1mm thickness around 15 USD, is set and fixed on the wet stone by an extensional bolt. This tool is used for the rough (#180) and middle (#400) grinding stage, holding the thin-section by your finger to keep on the rotating disk with water poring. After masterly, the thin-section reaches 0.1mm or less thickness for a few to ten minutes.
Nevertheless, the final fine grinding is still processed by hand like the traditional method. Because even a finer grit #1000 or much always makes scratch scars on the thin-section surface. In the final hand grinding, #800 carborundum and #1500 alundum + water are used on the glass plates. After completed grinding, a cover glass is glued on the thin section using soft UV resin. UV resin is useful because it causes fewer air bubbles than the traditional Canada balsam. After the cover glassing, the resin is cured with UV light or sunlight. Finally, the surplus resin is removed by a cutter knife and manicure remover (acetone). The name label is put on, and the thin-section is completed.
By our method, the total time is shortened almost around one hour to a couple of hours excepting gluing time, while the traditional way takes almost a half to a full day. This method provides more parallel surfaces and less defective thin-section compared with the traditional making process.
In the future, we try to mechanize the final stage; however, now we can not succeed in solving the scratches problem. After the introduction of our new tools, almost 200 new thin-sections are completed successfully. Such making process of thin sections and machines are not so complicated for a student's practice. So, it may be suitable for the geoscience club activities at the senior high school level.
In our trial, for the rock saw, we use a 150mm twin bench grinder as a base machine, and one side of the grindstone is removed, including its cover. A water tank with a table made from acrylic plates is fixed to the base of the motor with bolts. For the rock sawing, a cheap diamond blade (160mm to 180mm diameter, 1mm thickness) is mounted on the motor shaft with arbors, which is made using a table-top lathe machine. Except for this lathe operation, most of the processes can be completed with usual electric tools. For the cutting of acrylic plates, we use a hand cutter and glue specialized for acrylic work. On the water tank, an aluminum 3mm thickness board, having a slit for the blade, is fixed as a saw table. Also, at the bottom of the tank, a draincock was drilled.
The rock sawing is carried out with a quarter filled water. For safety, we have to set the ground for the electric system. A 1mm thick diamond blade is useful for the generic rock sawing. We can smoothly cut around the fist-sized rock with enough motor torque. When we cut the glued rock sample attached to the slide-glass, we set a guide for thin rock sawing on the table using a cramped acrylic block. After some training, we can cut the section within 0.5mm thickness. For the rock and glass gluing, a 90-minute hardening "Bond-E" is used. Also, we use a hot-plate for rock warming to make glue more liquidity.
Next is rock grinding. Hand grinding is the primary way of traditional method; however, we use a new grinding machine based on a kitchen knife sharpener, which consists of a rounded wet stone, a water tank, and a motor. A diamond grinding disk, 180mm diameter and 1mm thickness around 15 USD, is set and fixed on the wet stone by an extensional bolt. This tool is used for the rough (#180) and middle (#400) grinding stage, holding the thin-section by your finger to keep on the rotating disk with water poring. After masterly, the thin-section reaches 0.1mm or less thickness for a few to ten minutes.
Nevertheless, the final fine grinding is still processed by hand like the traditional method. Because even a finer grit #1000 or much always makes scratch scars on the thin-section surface. In the final hand grinding, #800 carborundum and #1500 alundum + water are used on the glass plates. After completed grinding, a cover glass is glued on the thin section using soft UV resin. UV resin is useful because it causes fewer air bubbles than the traditional Canada balsam. After the cover glassing, the resin is cured with UV light or sunlight. Finally, the surplus resin is removed by a cutter knife and manicure remover (acetone). The name label is put on, and the thin-section is completed.
By our method, the total time is shortened almost around one hour to a couple of hours excepting gluing time, while the traditional way takes almost a half to a full day. This method provides more parallel surfaces and less defective thin-section compared with the traditional making process.
In the future, we try to mechanize the final stage; however, now we can not succeed in solving the scratches problem. After the introduction of our new tools, almost 200 new thin-sections are completed successfully. Such making process of thin sections and machines are not so complicated for a student's practice. So, it may be suitable for the geoscience club activities at the senior high school level.