Hole saws have two different types of steel joined together to form the edge of the cutting end of the hole saw. High speed steel is joined to a soft spring steel to form a durable edge that will cut a multitude of materials and help provide long life. High speed steel is used on the outer edge due to its wear resistance properties and forms the cutting edge of the teeth. Soft, spring steel creates a flexible backing material that allows the hole saw to absorb impacts of the job of drilling holes in difficult-to-cut materials.
Advantages of Bi-Metal Hole Saws
Most users prefer a bi-metal hole saw for the majority of their work because it is compatible with a wide variety of materials. It also cuts faster and smoother and with reduced vibration due to the variable pitched teeth. Hole saws have two different types of steel joined together to form the edge of the cutting end of the hole saw. High speed steel is joined to a soft spring steel to form a durable edge that will cut a multitude of materials and help provide long life. High speed steel is used on the outer edge due to its wear resistance properties and forms the cutting edge of the teeth. Soft, spring steel creates a flexible backing material that allows the hole saw to absorb impacts of the job of drilling holes in difficult-to-cut materials.
A good bi-metal hole saw will easily cut through softer materials, such as plastic and wood-based items, as well as harder materials, such as steel and stainless steel. The type of high speed steel chosen by the hole saw manufacturer will contribute greatly to the performance of the hole saw. The best bi-metal hole saws will be made with high speed steel that has a high percentage of cobalt content. Manufacturers such as Milwaukee® use only Matrix II high speed tool steel in the manufacture of their bi-metal hole saws. Matrix II contains approximately 8% cobalt to help maintain tooth hardness at high operating temperatures, which helps to maintain the teeth's sharpness of the cutting edge.
More important to users is the life they will get from their bi-metal hole saw, or how many holes they will be able to cut before needing to replace it. In addition to using high speed steel with cobalt, the heat treatment process used by the manufacturer will impact the life expectancy of the hole saw. Milwaukee® uses a proprietary cryogenic hardening process that improves upon the traditional heat treatment cycle by using sub-zero temperatures as part of this process. This process improves the microstructure transformation of the high speed steel and results in a product that stays sharper longer. All of Milwaukee's bi-metal hole saws are treated with this Ice Hardened™ cryogenic hardening process which deliver up to 50% longer life than other hole saws in the marketplace.
One common frustration users have with cutting holes with a hole saw is removing the plug, or slug, from the cup after the cut is complete. Look for slots that are accommodating to easily work the plug from the cup. Milwaukee's hole saw design features wide, angled and offset slots to easily access and remove plugs from the cup. In addition, the type of plug will also impact how easily it can be removed. Milwaukee's Ice Hardened™ bi-metal hole saws are created with a set, or kerf, that cuts slightly biased to the inside of the hole saw, creating more clearance between the plug and the cup, making it easier for the plug to be removed.
Tips on Arbors and Pilot Bits
Cutting a hole with a hole saw requires the use of an arbor and often a pilot bit. Arbors, also called mandrels, are designed to connect a hole saw to a drill chuck as well as hold the pilot bit. They are made from hardened steel and alloy steel components for long life, as they need to last through multiple hole saws. Arbors connect to the hole saw with a thread in the cap of the hole saw. Hol"-18 thread drives hole saws 1-1/4" and larger. The larger hole saws (1-1/4" and larger) also have drive pin holes in the cap which receive drive pins from the arbor to facilitate quick and easy changes of the hole saw. Smaller hole saws connect to the arbor only with the thread and often get locked onto the arbor requiring tools to remove the hole saw.
There are quick-change systems in the market to help with quickly changing small hole saws on the arbor without the use of supplementary tools. The best sawing systems are universal. They will operate as a quick-change system with any brand of hole saw. Also, look for systems that don't require the use of any proprietary components or adapters to operate. These adapters often lock onto the hole saw and may require the use of tools to remove the hole saw and may not deliver the tool-free changes you are looking for. Milwaukee® recently launched the new Twist Release™ quick change arbor for tool-free operation with these smaller hole saws. This system works with all major brands of hole saws and doesn't require the use of any adapters to operate.
Pilot bits take most of the punishment in hole saw drilling. Many users drill with some oscillation movement to help clear chips from the cut. This puts a lot of side pressure on the pilot bit. Milwaukee® uses the Thunderbolt® web pilot, a tapered web design which offers a thicker core than standard pilot bits to protect against side-load breakage. It also features a 135° split point tip, which starts on contact to keep the bit from walking and helps ensure an accurately placed hole.
When drilling holes with a hole saw, you need a complete system designed to deliver the performance you need to do the job. This means all components of the system, not just the hole saw, need to provide you with durability and performance. When you choose the right system, you'll find that cutting holes has never been easier.
Article courtesy of Milwaukee Electric Tool Corporation