Hammer drill, Impact Wrench, How They Work, What You Should Know

Hammer Drill,
How It Works, Interesting Things To Know
Hammer drills have been around a long time. Hammer drills have been the choice for many operators when drilling into materials such as cement, concrete, brick, stone, block, and other masonry materials. The way the hammer drill works is to hammer as the drill bit is rotating. In theory they pulverize the hard material under the bit as the bit churns into the surface. In reality, the bit cuts into the surface with the help of a vibrating chuck. A masonry bit is used for drilling. The bits are exposed to tremendous friction as the operator bears down on the drill. The drill bit at the surface gets extremely hot. So, the very tip is made out of carbide steel by many manufacturers. Even though the tip is carbon steel, the tip of the bit get so hot that they discolor. If the tip of the bit is allowed to “blue”, the tip becomes brittle. Soon the operator notices chips in the bit tip. The bit tip then begins to break and drilling becomes hindered. In a short time, the operator notices that progress has stopped. There is a way to minimize this problem. Start drilling with a small bit first. Then drill the hole with progressively larger bits until the correct diameter is achieved.
Picture of a typical hammer drill.
Picture showing the insides of a hammer drill, labeling the various parts.

The picture above shows the various mechanisms inside of the hammer drill. In the center is the motor inside of the motor housing. In front of the motor is a cooling fan attached to the motor shaft.A bearing in front of the motor shaftsupporsthe fan.A rear bearing ishoused in black at the right side of the motor.

Picture showing a clear closeup view of a hammer drill, labeling the internal parts.
In picture 3 above, the motor shaft is shown passing through the Hammer Mechanism body where there are bearings that support the shaft. The shaft ends in a Worm Gearthat transfers motion to a large reduction gear. In the center of the Large Gear is attached a second shaft which runs out, and is attached to, and drives the chuck. On the top of the drill is a rotary switch. The rotary switch selects one of two modes of operation. Position right, counterclockwise, selects the drill only mode. Position left, clockwise, selects drilling with hammering. There is a pin shown attached to the wedge and rides in a slot in the rotary switch. When the rotary switch is turned clockwise, the wedge moves downward and forces the Hammer Mechanism forward. This engages the hammer action.

Picture showing the internal hammer mechanism of a typical hammer drill.

In the picture above, the Large Gear was removed from the drill and stood on the chuck. The drill body was stood on its end, and the Hammer Mechanism was moved out of alignment for viewing. Both the Large Gear and the Hammer Mechanism are ribbed. The Hammer Mechanism is stationary. The Large Gear turns and bumps along producing the hammer action.

Picture showing a closeup view of the main spring, large gear, hammer mechanism, and main worm gear of a hammer drill and functioning together.
The spring in Picture 5 above holds tension, allowing the hammer action. The shaft moves left and right causing the chuck to hammer the drill at the material while turning.

The problem with this kind of a design is the hammer mechanism. As can be seen in Picture 4 above, one ribbed surface is rotated against a stationary ribbed surface. At slow speed, the ribbed surfaces can actually fit into one another. As speed increases, the ribs have a tendency to walk or not fully engage as the Large gear turns or the spring weakens with age. This results in a shorter stroke of the chuck. In fact, at high speed, this hammer action is more of a vibrator than a hammer.

Hammer drills are notorious for drill bits coming loose while drilling. The vibration made by the cam causes the chuck to loosen on the drill bit.

There is an alternative to using a hammer drill that produces better results. An impact wrench contains a hammer that works very well in this application. For one, it has a much better hammer. Number two is the fact that under pressure it slows down minimizing heat buildup. Number three, the pneumatic version does not get hot as electric drills do. Unfortunately, you cannot attach a drill bit to an impact wrench directly. You will need a special chuck called a Cowan Chuck. For more information go to www.cowanchuck.com.
IMPACT WRENCH, How It Works, Interesting Things To Know

Picture of a typical pneumatic impact wrench.

Picture of a typical electric impact wrench.
Picture showing the various parts of a pneumatic impact wrench in an exploded view format. Each part is labeled for instructional purposes.
In Picture 8 above, a pneumatic impact wrench is shown disassembled. Air is forced in the adapter and up through the handle.In Picture 9 below, the housing is turned on end so we can look inside. There are 2 holes inside on the bottom. Air is forced through one of the 2 holes determined by the position of the FORWARD/REVERSE CONTROL BUTTON/VALVE. Air passes through a hole in the mechanism to the rear plate. The rear plate then channels the air into the ROTOR CYLINDER where it comes in contact with the ROTOR BLADES. The blades sit loosely in the rotor.Gravity causes at least 1 of the 6 blades to extend out of the rotor that catches the airflow. This begins to turn the rotor. Centrifugal force moves the rest of the blades partially out of the rotor where they glide along the inside of the ROTOR CYLINDER. This aids the turning of the rotor. The central shaft of the rotor passes through a bearing housing. The end of the shaft has a spline in it. The spline forces the HAMMER CAGE and HAMMER to rotate with the rotor (See Picture 10 & 11.). The HAMMER rocks on a pin going through the upper part of the HAMMER and its HAMMER CAGE. Notice that the hammer has a cut out on the right side. That is because a rocking lever, overly slotted, rides there. The lever, rocking back and forth, causes the hammer to rock in and out.
Picture of a pneumatic impact wrench internal housing showing the air channels for reversing the rotor direction.
A good closeup picture showing the impact wrench internal rotary hammer and how it works for instructional purposes.
A closeup picture of the impact wrench hammer mechanism and how it interfaces with the anvil and motor mechanism.

Here is how it works (refer to pictures 8, 10& 11). With no air pressure applied, the ANVIL is relatively free to turn in either direction. Application of air pressure forces the rotor to turn. The spline forces the rocker lever to move. This forces the HAMMER and HAMMER CAGE to rotate. The HAMMER rocks into the ANVIL’s slot. The ANVIL starts turning. As long as air pressure is applied, the HAMMER tries to remain engaged into the ANVIL’s slot.

What happens when the ANVIL meets resistance as with a bolt and socket? Pressure builds up in the ANVIL’s slot. The HAMMER has a matching grove in it so that it will fit into the ANVIL’s slot when rocked. It’s grove is slightly rounded so that when a lot of reverse pressure is applied, it will slip out of the grove. The HAMMER, CAGE, and ROTOR make 1 full revolution. Pressure is still applied. When the HAMMER meets the ANVIL’s grove again, it slams in giving a hammer blow to the ANVIL. If the ANVIL does not start moving with the HAMMER, CAGE, and ROTOR, the HAMMER slips out of the grove again. The process then repeats itself.

A hammer action like this is great for bolts and nuts. With a drill chuck attachment, this device would make a good hammer drill. Why? An operator would apply some downward pressure. That gives us a “Y” vector. The hammer/rotating action gives us an “X” vector. Combining the 2 vectors gives us a resultant “Z” vector, as shown in the VECTOR DIAGRAM below. The resultant “Z” vector is longer than either the “X” or “Y” vectors. This means that the resultant force exerted for drilling is greater than the force of the impact wrench alone. That with very little operator pressure, the resultant force is never less than the force generated by the impact wrench. A hammer drill can be made from an impact wrench with the use of an Impact Wrench Drill Chuck. Such a chuck, called a Cowan Chuck can be found at www.cowanchuck.com.
Picture of a gragh showing the X and Y force vectors generated by the impact wrench and its resultant Z vector.
Picture of the Cowan Chuck, an Impact Wrench Drill Chuck, and an Impact Wrench Accessory.
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