What is an annular cutter?
An annular cutter is a specialized bit for magentic drills. Like a hole saw for wood, they only cut the outside edge of a hole. It produces an accurate burr-free reamed like hole. These drills make a much larger hole and requires less force and time than a standard twist drill bit. As it turns, the cutter produces chips from the outside cutting edges and after cutting the hole which leaves a chunk of steel from the center of the cutter then falls out.
Design Structure
On top of the cutter there is a hole for the pilot pin which is used to locate the center of the cut in a drill. Next, there are Flats on the sides which hold the cutter in place in the magnetic drills. The shank which is either ¾ or 1-1/4 diameter which slides into the drills. On the cutting edge there are flutes that pull the chips out of the hole when cutting. And last the cutting teeth, which have different angles called Geometry that makes the cut.
Key Advantages
There are many advantages of using these to cut holes rather than traditional drill bits such as twist drills
Cutting Time
The big advantage that these cutters have is that it doesn’t drill the entire hole but rather it creates a peripheral cut around the hole as the cutter drives into the metal. The hole’s thickness matches the thickness of the cutter’s wall. A twist drill bit cuts the entire hole rather than just the periphery so this takes a longer time. These cutters are 3 times faster than a twist drill and require no step drilling.
Another big time saver is material removal. With twist drill bits the bit has to be pulled constantly so that the swarf can be pulled out. With mag drill bits the material is automatically ejected as the bit drills which saves a lot of time when drilling multiple holes.
Post Project Cleaning
Because of the angled teeth and unique design of these slugger bits can drill through metal leaving very few chips and material to clean up after the project is complete. The sluggers are designed to move material through the recessed edges along the side of the bit to the outside as it cuts in deeper. It is possible to achieve burr free finishes once the hole is complete without any additional.
Heat
Because of the significantly lower amount of material that is removed in a short amount of time, annular cutters can be a lot cooler than twist drill bits. Twist drills remove a lot of metallic material as it drills into the hole and the temperatures can be very high and oftentimes far too dangerous to touch. Annular cutters with cutting fluid can be ideal to keep temperatures to a very reasonable level.
Longevity
With more blades working cohesively to cut holes, slugger drill bits last longer than twist drill bits which warp and dull faster. Since cutting fluid is a necessity when making holes with annular cutters, the heat is greatly reduced which also reduces warping and other defects along the bit.
Styles
The cutter you select depends on the diameter of the hole, the depth of cut and the type of material. There are a wide range designed to cut through the following materials: Carbon Steel, Stainless Steel, Hard Alloys ex: Titanium and aluminum. The most common cutter is high speed steel annular cutter, and is the standard with most cutters. Some other types are more specialized like cobalt annular cutter are effective when drilling material with inconsistent composition. Carbide mag drill bits are used for hard or abrasive materials. Titanium Nitride Cutters or TINI cutter have coatings that improve tool life by increasing surface hardness of the tool and providing greater lubricity. TINI coated are generally used in applications where the material being cut is difficult to machine, or when extended tool life is desired.
Depth and Diameter
When determining cutter size, they are measured by depth and diameter. If you look at an actual cutter the depth is actually longer than what it is rated, (a 1" cutter is really 1-1/4") because this ensures the tool can drill all the way through the hole and allows extra length for resharpening. Mag drill bits either come with a ¾” or 1-1/4 weldon shank depending if you’re using Magentic drill. Some cutters require special arbors to fit properly.
High Speed Annular Cutter vs. ID or Stack-Cut Geometry
Most mag drill bits come with Standard geometry. They are designed to cut through one piece of steel and offer the fastest, and cleanest hole. When the job requires drilling two or more pieces of steel plate, cutters with stack-cut geometry must be used. This special cutting geometry enables two or more steel layers to be drilled in a single operation with a mag drill. The cutting geometry causes the core to be cut from the inside to the outside. This produces a cylindrical core without a protruding burr at the lower end.
Annular Cutter Pilot Pins
A Pilot pin is a large nail looking object that helps start the hole when using an annular cutter. It serves three very important functions it locates the center of the hole. Allows coolant to flow down around the slug and to the cutting teeth and ejects the slug at the end of the cut. Pilot pins tend to last a very long time and can be used with multiple sizes of cutters.
Extending Cutter Life
Coolant and cutting paste increases tool life dramatically. Cutting fluid is a water-based fluid designed to protect galvanized, steel, aluminum, brass and other alloys, it extends tool life, improves surface finish and reduces heat buildup. Drilling with a mag drill bit upside down can cause fluid to leak from your drill. Instead use cutting paste that is applied to the inside and cutter teeth to reduce heat buildup and extend the life of the cutter.
How to resharpen a mag drill bit?
Re-sharpening your high-speed bits makes them like brand new. You can sharpen your cutters up to 6 times as the cutter are reground on the same CNC machines the cutters were manufactured on to ensure they are true to size and just as sharp as day one.
Hole Saws or Annular Cutters? What is Right for You
Hole saws are a lot cheaper than annular cutters but you get what you pay for. Overheating, warping, and limited repeat use are common problems with hole saws. Hole saws do not have flutes that eliminate the chips that are formed as the drilling is performed. A mag cutter has a bigger initial cost but with resharpening and proper care they can be used for years without replacing. If you are cutting a thin sheet with very limited repeat use then a hole saw can do the job but for longer and deeper cuts the annular bit will be the right choice, especially if you already own a mag drill.
Best Brands for Mag Drill Bits
Some of the more popular brands that manufacture annular cutters are Fein, Milwaukee, and Hougen. Hougen and Fein seem to be very popular and both manufacture durable cutters that are ideal for repeated use. Fein manufactures Jancy cutters which are extremely popular and fits the Fein magnetic drills. Milwaukee mag drill bits are designed for use on their mag drills. We recommend using Jancy cutters because of the durability and efficiency it provides in cutting compared to other brands. Hougen comes the closest in terms of durability and they have engineered some of the best bits on the market.
The most common sizes
Different applications call for different sizes, the most popular diameter sizes are 7/16” annular cutter, 1/2”, 9/16”, 5/8”, 11/16”, 3/4”, 13/16”, 7/8”, 15/16” and 1”, that have 1” and 2” depth of cut.
There are many brands that make mag drill bits, some are imported, and some are made in the USA and prices vary, each manufacturer sells different sizes and sets, some include the pilot pins and some do not. Brands, like Jancy, Slugger, Fein, Evolution, Steelmax, Hougen, Unitec and Milwaukee are just some of the companies that make great hole cutters.