7.1 Introduction
Tim A. Bacon
Keep your fingers away from anything moving, at least the ones you want to keep…
Saws are used frequently in machining and while they are very useful tools, they present severe risks to machinists. To stay safe, know the risks, and follow recommendations to protect yourself. Here are some general guidelines to keep you safe when using saws.
- Keep your hands and fingers away from the blades until everything has stopped moving, and not before.
- Do not wear gloves. Although the part may get hot, and wearing gloves may seem like a good idea, do not do it! Gloves can get caught in the blade and pull your hand and fingers into the saw. If you need gloves to clean up, make sure that none of the equipment is running while you clean.
- On the vertical bandsaw, use something other than fingers when pushing material through the saw. Keeping your fingers away from the blade is a good way of ensuring that you will still have them at the end of the day. A good alternative to fingers is a stick of wood for pushing parts into the blade.
- When making cuts on a vertical bandsaw and the blade gets stuck, it might be tempting to pull back on the part instead of pushing straight through. The hazard with this approach is that if the material catches the saw blade, it will pull the blade off of the track and possibly damage it.
- The three tooth rule says that the thickness of the material being cut needs to be at least as thick as the distance across three teeth. If less than three teeth are engaged in the part, try stacking parts to make the material thicker. Another option would be to place the part on top of a scrap piece of material to increase the number of teeth that are cutting. See section on saw operations for more detail.
Similar to the three tooth rule for thickness, the RPM (speed) of the saw needs to be considered. In general, use a fine-tooth blade with a slow rpm for steels, and a coarse blade with a high rpm for aluminum.
A chip is a splinter of material that comes off of a larger piece of material being cut. There is a more detailed discussion of types of chips in the chapter on general machine shop safety. Two things need to be present to make a chip: Heat and pressure. The heat comes from the saw moving over the top of the part, and the pressure comes from the force applied to push the blade into the part. In some cases, the part is pushed into the blade.
One of the first operations in the machining process is to saw material down to a size slightly larger than the finished part. This smaller piece of material is referred to as the stock. Consideration of how the stock will be held during machining and the cost of the material will dictate the final stock size. If the material comes into the shop in long lengths of bars, it is cut up on the horizontal bandsaw. If the material is smaller in size and can be readily handled, it is cut on the vertical bandsaw. If the material has been hardened, it may be necessary to use an abrasive saw to cut the material.
Author’s Tip
Fingers and moving parts should never exist in the same place at the same time.
Housekeeping and Preventative Maintenance
The tools and machines in the shop must be treated properly and well-maintained to keep the shop running safely, efficiently, and economically. There are many ways that machinists regularly tend to shop functioning. For instance, machinists must use the right equipment for the job they are doing. if a piece of hardened material is put into a horizontal bandsaw, the blade will become dull in a short amount of time. This will cause a loss of production time while the blade is replaced and add the expense the of purchasing another saw blade. Properly matching the job to the saw will ensure that the saw blade lasts for a long time to come. Taking care of equipment in this way is considered good housekeeping. In fact, taking care of the equipment should be a routine event. Throughout the day, cleaning off the table, making sure there is coolant in the tank, and mopping up the splashes from the coolant are just some of the common housekeeping activities that take place in the shop.
Aside from keeping the equipment clean, preventative maintenance involves ensuring that a proper blade is matched to the material being cut. If the wrong blade is selected or something happens to damage the blade, a new one will be needed. To replace the blade, the cabinet that covers the wheels on either side of the cut area will be opened. There is a handle that will relieve the tension on the blade so it can be removed. When handling saw blades, care must be taken to avoid personal injury. Note the direction of the teeth on the blade before removing the bad one to ensure the blade is placed into the saw properly. After the saw blade has been installed, rotate the wheels as the tension is increased to ensure the blade is seated before operation. Close the doors to cover the wheels before starting the saw for safety.
Finally, it may not be obvious, but the shop’s layout is designed with housekeeping and equipment care in mind. Grit from the chop saw is like dust and it spreads out in a wide area when cutting material. The grit is abrasive and can promote excessive wear on moving parts. Because of this, the chop saw is commonly placed in an area that will help control the spread of grit.
Workholding
Safety needs to be considered when setting up workholding. A part that is not held securely while being worked on can present a significant risk of injury to the machinist. Material to be cut comes in a variety of shapes. Square, rectangular, and round shapes tend to be the most common. Small parts can be cut by hand on the vertical saw, while longer parts need to be cut on the horizontal saw. On either style of saw, the round parts are a challenge because they will want to rotate with the blade. Clamping an angle bar, or another piece of material to the round bar will help to keep it from rotating when it is being cut. Assertive clamping pressure with a conservative feed rate of the blade will assist in providing a successful cut and the safest operation.
Use a level to ensure material on a stand or table is at the proper height to cut on a horizontal bandsaw. This will help the blade make a perpendicular cut on the part, which will save material and money. If the blade cuts at a slant across the material, material is wasted.
The horizontal saw has a vise that pivots to conform to material that does not have parallel sides. When cutting short parts on the horizontal saw, both sides opposite the pivot point on the vise need to be supported. If only one side is used to clamp the part, the vise will clamp at an angle and likely release the part while it is being cut. When the part comes out of the vise while it is being cut, there may be damage to the part and/or the saw blade.
The chop saw uses a pivoting vise similar to the horizontal bandsaw. It can accommodate parallel parts. When a short part is being cut, both sides of the pivot point on the vise must be supported to ensure proper clamping of the material.
Attributions
- Figure 7.1: The three tooth rule by T. Bacon, courtesy of Bates Technical College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 7.2: Push stick by T. Bacon, courtesy of Bates Technical College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 7.3: US Navy 100117-N-6070S-005 A member of the Los Angeles County Fire Department Search and Rescue team uses a heavy-duty saw to cut debris away from a collapsed building in downtown Port-au-Prince by U.S. Navy/Mass Communication Specialist 2nd Class Justin Stumberg in the public domain; This file is a work of a sailor or employee of the U.S. Navy, taken or made as part of that person’s official duties. As a work of the U.S. federal government, it is in the public domain in the United States.
- Figure 7.4: Sierra Cinta OAV2 by Jet~commonswiki is released under CC BY-SA 3.0
- Figure 7.5: Cutting round stock by T. Bacon, courtesy of Bates Technical College, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 7.6: Using step blocks by T. Bacon, courtesy of Bates Technical College, for WA Open ProfTech, © SBCTC, CC BY 4.0
The principle of having a minimum of three teeth of the saw blade engauged in the material
A circular saw which is typically used to cut hard material, such as metal, tile, and concrete with an abrasive disc.