Annular cutters are tool that are used to make hole in metal. Unlike twist drill, annular cutters only remove the ring of material from the metal to make the hole; the metal that are removed is referred to as the slug. Because annular cutters only remove the ring of material, the annular cutter require less power from the motor to create the hole.
Thus, because annular cutters require less power to perform the task of drilling holes in metal, annular cutters are more efficient than twist drill at drilling holes in structural steel. Annular cutters must have the correct diameter chosen for the task to be perform. The diameter of the annular cutter should match the size of the hole that is to be cut in the steel; small holes will require small diameter annular cutter, and large holes will require large diameter annular cutter.
How to Choose and Use Annular Cutters
A size chart can be used to determine the correct diameter of the annular cutter based off the size of the hole that is to be drilled. The depth of the annular cutter to be purchased should also be considered in relation to the thickness of the metal to be cut. If the annular cutter is too deep, it can create heat in the metal being drilled; if the annular cutter is too shallow, it will not complete drill the hole.
Thus, ensuring that the depth of the annular cutter is matched with the thickness of the metal will prevent the annular cutter from overheating or stall in it’s task. Another factor to consider is the shank style of the annular cutter. The shank must lock into the machine that will drill the metal.
Magnetic drill table use flat Weldon shanks, but other machines, like drill presses, may use a Morse taper shank. Quick lock arbors are often used for efficiency in high volume workshops; however, the spring pins in those arbors can wear down causing the tool to not drill proper. Thus, you should confirm the shank style before purchasing annular cutters to ensure that they will fit the machine.
Another purchase to consider is the material grade of the annular cutter. High speed steel will work for cutting mild steel; however, it is not recommended for cutting stainless steel due to its rapid work hardening. For cutting stainless steel, the cobalt alloy grade of annular cutter will be necessary due to its hardness relative to high speed steel.
For cutting aluminum, the use of a titanium nitride coated annular cutter will help reduce the friction between the metal and the cutter. For hardened steel, carbide tipped annular cutters will be able to handle the high Rockwell hardness of that metal. A size chart can be used to determine the proper material grade of the annular cutter based upon the metal that will be cut.
Two variables to consider when using the annular cutters are the cutting speed (RPM) and the use of coolant. The RPM that is used will be lower for the annular cutter than for a twist drill because the annular cutter remove less metal. For stainless steel, you must use lower RPMs and sulfurized oil.
For aluminum, higher RPMs and light lubricant are used. For hardened steel, low RPMs and constant flood cooling are used. Using the wrong speed and coolant will cause the cutting edge of the annular cutters to turn blue and the tool will no longer cut the metal cleanly.
The pilot pin attached to the annular cutters has two job. The pilot pin centers the annular cutter in the metal prior to cutting, and it ejects the slug that is cut out of the metal. If the pilot pin is bent or if its spring is weak, the slug will not be ejected from the metal.
Thus, regularly checking the pilot pin will ensure that it remains in proper working order and that the slugs will not get stuck in the holes cut by the annular cutters. To ensure that the annular cutters continue to perform their task properly, maintenance is required. Brushing the flutes of the annular cutters after each use will clean the tool.
Wiping the shank will remove metal particle that may stick to the shank. Store the cutters in a way that the teeth do not touch each other. High speed steel cutters can be resharpened, but you should perform a visual check to ensure that the teeth have not chipped during use.
All of the factor that relate to the annular cutters can be determined by the size chart. Each of the factors interact with each other in the cutting of metal. Thus, by using the size chart to plan the cutting of metal, the tool will behave in a predictable manner.
