A Magnetic Drill Primer

Look at required hole diameters rather than horsepower when selecting a mag drill

Two-stage magnetic drill.

The Hougen HMD505 has a two-stage magnet that fully engages when the motor is turned on, helping to ensure the operator’s safety. Photo courtesy Hougen Mfg.

Many options are available when you are selecting a magnetic drill, but you can narrow down your choices by looking at five variables: the application, the diameter of the hole being drilled, the depth of the hole, the material, and the type of tooling.

These five variables will start the selection process, but size limitation, weight, and the work environment will also be determining factors.

One of the main uses for magnetic drills is holemaking in structural steel applications. Metal fabricators, maintenance workers, welders, and even ship builders make use of this technology.

According to Randy McDonald, national training and product manager for FEIN Canada, the application is the largest deciding factor for choosing the appropriate magnetic drill.

“If you are outside, drilling small-diameter holes in structural steel, you may only require a small, lightweight, single-speed tool,” explained McDonald. “If you are drilling and tapping large-diameter holes in-house, you will need a more sophisticated drill, possibly with two speeds and electronic speed control.”

Most small, lightweight mag drills have a single speed and the larger, more powerful drills have two or more speeds. For drilling smaller-diameter holes, for example, those 1-1/4 in. and smaller, there is no real advantage in having more than one speed.

“When you are drilling larger holes, having more speeds allows the operator to get the cutter closer to the correct RPM for the hole diameter and material,” said Greg Londrigan, marketing coordinator for Hougen Mfg. “This increases tool life for the cutter, reduces the wear and tear on the motor, and also decreases the amount of physical work performed by the fabricator.”

The choice between single and multiple speeds mainly depends on the application.

In structural steel applications a single-speed machine typically is satisfactory. However, a machine used in a shop might also be called in to service for drilling, reaming, countersinking, and tapping. These applications require a machine with more than one speed.

“The type of material and cutter choice also have an effect on the speed requirements,” said McDonald. “If someone is using HSS [high-speed steel], carbide cutters, and twist drills, they will need a machine with more than one speed. This is where variable speed plays an important role. Most [mag drill] manufacturers offer both single- and multiple-speed machines.”

FEIN magnetic drill.

Predictable work times on contract and serial work is possible because of the FEIN KBM 80 auto’s repeatable and consistent drilling times. Photo courtesy FEIN Canada.

The work environment also should be taken into account when you are selecting a drill. Space and physical limitations must be considered.

“If you are in a very tight area with low height, you must choose the drill that fits into the area, but this can also be difficult depending on the size of the hole being drilled. If you are working overhead, you would also want a drill that is lightweight,” said McDonald.

But this again, depends on the diameter of the hole and type of cutter being used.

“If the application is in small or confined spaces, a lightweight, low-profile drill would be a perfect choice. In a large, open fabrication facility where height is not an issue, a larger two-speed mag drill might be a better overall choice,” said Londrigan.

Hole Diameter

The size of the hole being drilled is another key variable because it will determine how much horsepower is required. It is best to pick a drill unit that is rated to cut the size of hole your application requires.

But, choosing a mag drill based on rated HP alone often can be confusing and misleading, said Londrigan.

“Mag drills should be selected according to the maximum hole diameter that is going to be drilled and the type of cutter being used,” said McDonald. “This dictates the power (wattage/HP) that will be required. If you are using a ½-in. by 1-in. HSS annular cutter, you can use a small mag drill with lower power. But if you are drilling a 1¼-in. hole with a solid twist drill, you will require a much more powerful machine.”

All manufacturers list the maximum rated capacities for their magnetic drills along with their power ratings. You should never use the drill at a higher rated capacity than the manufacturer lists because this can lead to overload situations and possibly result in the magnetic base lifting off.

Feed choice, whether it’s manual or automatic, also needs to be decided before selecting a mag drill.

Most magnetic drills use manual feed, which typically costs less than power feed because it does not require the additional drive motor, parts, and electronics that come with an auto-feed drill.

Right angle drill.

Right angle mag drills have a lower profile and can be used for hard-to-reach applications. Photo courtesy Hougen Mfg.

According to McDonald, manual feed is best-suited for applications that require twist drills, especially when drilling blind holes or tapping. In addition, certain accessories, such as those for countersinking and reaming, are better-suited to a mag drill with a manual feed.

“When drilling in difficult areas or tight situations, manual feed can also be the best and safest option,” said McDonald.

Auto-feed drills typically are used in high-volume applications because of their ability to create repeatable holes and consistent work times. Also, a single operator can run multiple machines.

“Auto-feed drills offer predictable productivity with consistent results and hole finish. When the cutter is fed at the same rate for every hole, over time tool life can be easy to gauge,” said Londrigan.

Using Lubricant

Because lubricant is important for tool life, most drills are equipped with a coolant reservoir, which is set up to provide the best coolant flow to the annular cutter. This provides constant coolant to the teeth of the cutters, which is where lubrication is needed the most, especially when drilling thick material.

“Just spraying coolant at the cutting tool is a waste of money; most of the coolant will just fly away, with very little getting to the teeth of the cutter,” said McDonald.

If internal lubrication is not possible, such as in overhead applications, coolant pastes or waxes are available. Always try to use some type of lubrication to enhance cutter performance.

“Lubrication has a huge effect on the performance and life of the cutting tool,” said McDonald. “While you do not have to use lubrication, to extend the life and performance of the cutter, lubrication should be used.”

Using lubrication not only extends tool life, it also enables cutting speeds to be increased and reduces the amount of drag on the motor.

The Tooling

For drilling a through-hole with a magnetic drill, annular cutters are the No. 1 choice. Annular cutters cut faster, last longer, and require less torque and HP to make holes when compared to a twist drill.

“The difference is night and day,” said Londrigan. “For example, a small mag drill can drill a large hole easily in one pass. But if you are using a twist drill, you would need a very large, heavy, and powerful drill and take the time to start with a small hole and step it up to size. This requires multiple passes and a lot of time.”

With annular cutters step drilling is eliminated, and you can create burr-free, accurate holes in one step.

“Instead of drilling a solid mass, annular cutters remove a small ring of material rather than the solid hole. You can realize up to a 40 percent reduction in work time when using annular cutters,” said McDonald.

HSS and carbide-tipped cutters also are popular.

HSS annular cutters are frequently used on construction sites and for on-site installation work that involves mainly mild steel. In such applications, HSS cutters can be subjected to shock and impact loads, for which they are better-suited than carbide. HSS cutters will work in many applications, but in hard or abrasive materials, carbide is better.

“Whether you choose HSS or carbide-tipped annular cutters, they both offer the ability to drill holes in a wide variety of materials. For applications in standard metals and structural steels, HSS cutters work just fine, plus offer the ability to be sharpened multiple times. Each time a cutter is sharpened, it keeps lowering the cost per hole,” said Londrigan.

Additionally, coatings can be applied to the cutter to further expand its performance in various materials.

Carbide cutters also work well in mild and structural steels, but a mag drill that runs at a higher RPM is necessary to gain the benefits of using carbide. In harder materials, such as stainless steel, the real benefits of improved tool life are realized with carbide.

“For hard materials, carbide cutters have a very high tip hardness and offer much longer service life. They enable higher cutting speeds, but therefore require magnetic drills with high operating speeds,” said McDonald.