Chop Saws and Grinders 1. CHOP SAW 1.0 Function of the Chop Saw Chop saws are used to create a rough, initial abrasive cut in a desired material. In principle, a chop saw is an electrically powered motor which turns a high speed abrasive wheel. There is a wide variety of parts machinable by the chop saw. The chop saw can make an initial straight, abrasive cut in a material to either make the piece of better workable size or to create a rough outline of a desired shape. The chop saw is used in the initial stages of a project because of the draft quality present in it s work. 1.1. Safety Considerations Before using the chop saw, confirm the type of material to be machined. Then chose the proper blade to cut the part. Make sure the blade does not have any cracks or abnormalities, and is properly installed. 1.2 Safe machine and Tool Operating Parameters Chop saws, being a machine with high speed moving parts, has several safety concerns which must be observed when in operation. Read the wheel specifications for the maximum number of rpms (revolutions per minute) the wheel can handle, taking care not to exceed those design parameters. The corresponding speed (rpms) at which the chop saw will be running should be outlined in the product literature and often times on the machine itself. Note: Be sure you are using the proper saw wheel for the proper material. If one has any questions about which wheel to use, the speed at which one can operate it, or any other questions, ask the instructor before proceeding. The first major concern is when bringing the wheel down to commence cutting. Do not drop it onto the material! However, slowly let the wheel touch the material, then follow through as the abrasive cut is made. This could chip the wheel and may result in fractures or breaks in the cutting wheel, thus sending high speed particles flying off in any direction. In addition, chop saws, unlike conventional shaping devices, do not perform a cut but rather an abrasion. There is a spring mounted guard that keeps sparks confined as well as protect the user from potentially broken blades. Safety glasses should be worn to give protection from the heat of the sparks.
2. GRINDERS 2.0 Function of Hand Grinders Grinding is the removal of metal by a rotating wheel; the action is similar to that of a milling cutter. The wheel is composed of many small abrasive grains, bonded together, with each grain acting as a miniature cutting tool. The process, depending on the wheel type, can produce extremely smooth, accurate finished to rough shapings. Because only a small amount of material is removed at each pass by the wheel, grinding machines require fine wheel regulation. The pressure of the wheel against the workpiece can be made very slight, so that grinding can be carried out on fragile materials that can not be machined by other conventional devices. Hand Grinders are tools that are designed to do several jobs in the field, including grinding flat surfaces, wire brushing rust or paint from a workpiece, and buffing or polishing a finish on a workpiece. Hand grinders are of two basid designs: the straight and the offset or angle type. The straight or horizontal grinder is most often preferred when the job is a curved or circular surface, such as a hole or a shaft. The two main features of the working or spindle end of the grinder are the wheel guard and the spindal friction clamping assembly. The wheel guard is a metal shield that normally covers approximately one half of the grinding wheel or wire brush. It shields the technician from grinding particles, wire particles or shattered grinding wheels which may fly into the face and eyes. The angle or offset grinder, is most often used for flat surface work where excess welds from plates must be removed or in some cases merely grinded off of high spots or edges. The construction of the offset grinder is basically the same as the straight grinder except for it s mode of operation. The spindal is at 90 degrees to the grinder housing, with a metal guard surrounding almost one-half of the grinding wheel. To meet the wire brushing and polishing needs of the technician, several forms of accessories are available. The straight grinder uses a straight grinding wheel. This means that work is performed only on the outer rim of the wheel. Wire brushes for straight grinders are made to perform on their rim face. Wire wheels are also available for the offset grinder, but these are of the cup design. Buffing discs for both the straight and offset grinders are available to polish metals such as brass, aluminum, or stainless steel. 2.1 Safety Considerations 1. Unplug the machine before working with the wheel. 2. Always wear goggles or a face shield when performing any grinding operation. 3. Never put a wheel on the grinder before checking it for soundness. 4. Do not attempt to use a grinder unless the wheel guards are in place and securely fastened. 5. Check the machine thoroughly before using it.
6. Keep your hands clear of the rotating grinding wheel. It is a cutting tool and can cause serious injury. 7. Always stop the machine before making adjustments. 8. Never force work against the grinding wheel or use a wheel that is glazed or loaded with metal. 9. Never operate a grinding wheel at speeds higher than recommended by the manufacturer. 10. Do not strike wheel against the surface you are working on. 11. The wheel will generate a lot of heat. Let it cool down before you adjust or replace it. 12. Check the direction of the sparks to make sure no one is in the area. 13. Always keep eyes on the work. 2.2 - Newer Developments (recent improvements) Grinders have been improved somewhat over the years. They have been made safer by improvements in guard design and safety switches and locks. As the materials that are used in machine shop applications are constantly being changed and improved, the materials used in the grinding wheels must also be improved. New materials and production techniques have resulted in different grinding wheels for different applications. Some examples would include aluminum oxide being used to grind steel shanks, and a silicon carbide and diamond wheel being used to grind carbide tipped tools. The newest in industrial level grinders is the compressed air, turbine grinder. This design allows for increased horsepower, lighter tool weight, less handling torque, higher rpms and increased overall productivity. Also, it allows for a decrease in tool vibration, which is known to cause numbness in extremities. However, in relation to this high productivity is a higher purchase cost. 2.3 Environmental Concerns There are two kinds of environmental concerns that apply to hand and pedestal grinders. The first is immediate environment concerns to the user in the machine shop. Grinders cut or shape metal by way of abrasion, therefore there is a lot of dust or debris that results from this process. Users of these devices should take extra precaution to protect their eyes and avoid inhaling debris. Also, a great deal of heat and sparks can be generated by these machines and the user should take precautions to avoid being harmed or harming someone else near by. The second type of environmental concern is more global. The safe disposal of the waste created by these machines is a concern that the user must be aware of. This waste may be in the form of chips or shavings from the material being worked, debris from the grinding wheels or lubricant from wet grinders. It may be possible to recycle some of this waste.
2.4 Information for Design of Parts for Safe Machining There are pre and post processing techniques that can be used to make working with a grinder safer and more effective. The use of tool rests and guides can make the work easier and more precise. Special care should be taken in selecting the proper wheel for the material that is to be worked with. While using a grinder, dipping the work from time to time in a water bath will avoid overheating. Also by not applying too much pressure, burn marks and discolourations can be avoided. Hand grinders are also very handy for removing burrs and other imperfections from items that have to be worked on with other machines. They are also used for finishing or fine tuning.