Portable Power Drills

Written: 30 January 2011 Ronald G. Darner

Temporary notes by Ron Darner


Use this link to access a "Table of Portable Electric Drill and Drill-Related Patents"

Written: 11 February 2011 Ronald G. Darner

Last Updated: 25 Feb. 2011 RGD

This tabular listing tracks patents I've reviewed, studied, printed, or otherwise encountered while conducting research on electric drills, their components, attachments, ancillaries, and conversion tools. My intent: simplify locating patents referenced only by date -- especially when part of the date may be illegible! -- and to cross-reference between dates and patents.


One chuck patent, assigned to Jacobs, is #2,346,706.

General chuck repair instructions are at http://www.jacobschuck.com/drill-chuck-repair.asp .

Removal and replacement are at http://www.jacobschuck.com/drill-chuck-install.asp , and there are other topics linked from http://www.jacobschuck.com/ .

For Rohm chucks, see http://www.travers.com/skulist.asp? RequestData=CA_Search&navPath=All+Products%2F%2F%2F%2FUserSearch1%3Drohm&q=block+id+37128+and+class+level3+id+28986&minPrice=$30.79 .

Travers Tool has more styles, also; if you look at http://www.traverstool.com and enter "Rohm" as a keyword, you'll see them.

There is a lot of information on repair parts, schematics, and nomenclature at http://d3cmirsdb60x3h.cloudfront.net/schematics/milwaukee/0100_72-1001.big.pdf .

and the more general http://www.ereplacementparts.com/milwaukee-electric-drill-parts-c-131_136.html?osCsid=nmr2464fo1qcf0sa17uq52sfa2.

In fact, eReplacementParts covers MANY brands: see http://www.ereplacementparts.com/.


A switch assembly patent is # 2,487,011.  It has a pin at the bottom of the handle, perhaps to get around a side-mounted button?  But I have a number of drills using it.

Housing & brush holder concept patent: # 2,693,541.  I've gathered a stack of patents, but will bore you with the list later


AC (Alternating Current):

Electrical power which reverses polarity at some frequency, usually 50 or 60 times per second. Some drills were made to operate at 25 cycles per second – a frequency sometimes supplied by independent hydroelectric systems in the past. There may have been drills made for use at 400 cycles per second (used by aircraft electrical systems).

Amps (Amperes):

The amount of current drawn by an electric drill.

Angle Drill:

(1) A drill incorporating bevel gearing so that the axis of the chuck is at an angle to that of the motor. (2) A right-angle drill.

Left: “True-Power”1; Right, Milwaukee2.


Something which may be used in conjunction with an electric drill to modify its capabilities. It may or may not take part in the actual use. A bench mount would be a passive attachment used to permit hands-free use. A drill press would be an active attachment providing additional accuracy and force. A bubble level would offer improved accuracy under some conditions, but not take any part in functioning of the tool itself.

Auxiliary Handle:

A separate piece which can be attached to the body of an electric drill or attachment, permitting use of both hands for additional control, or to add force along the axis. Many are threaded, and can be placed in various positions, typically right, left, or at the top of the drill body.


A stiff wire piece, usually in the form of a loop with both ends captive, and able to swing about those ends as a pivot. Functions include hanging for storage, or holding the trigger in the “On” position.


The components which separate rotating parts from stationary ones to reduce friction. These may be plain bearings or rolling-element bearings.


The assembly including the motor or motor housing, and the gear case; it may be built from multiple pieces, and – for this glossary - will imply a metal unit, or plastic if double insulated. Typical construction includes cast or die-cast parts joined by screws, or stampings with screws or threaded rods and nuts. Finish can be as-cast, polished, or painted.


The two pieces which carry electricity to the rotating part of the motor. They are usually held by a spring-loaded holder, and are replaceable. Blue arcing seen through the ventilating slots in the housing may be evidence that it is time to change them.

Central Handle:

Usually a straight vertical handle beneath the body of the drill, more common on larger and heavier types to improve balance.


Device made to hold the bit. Common capacities are 1/4", 3/8”, and 1/2", but others exist. Most have three jaws which close down upon the drill bit, but two-jaw types exist, and some early drills used tapers or setscrews.

Chuck Key or Chuck Wrench:

Device providing leverage to tighten or loosen the chuck; most are “T” or “L” shaped, and have a pilot and bevel gear which engage with a hole and gear teeth on the chuck.

Close-Quarters Drill:

An electric drill having an unusually short length in the axial direction, to permit use in locations such as between joists or studs. Often, the reduction gears are arranged so as to offset the motor from the chuck axis. Handles are often adjustable or movable to further improve utility in restricted spaces.


A closed loop, usually at the rear of an electric drill, often aligned with the axis of the chuck. The plane of the “D” may be vertical or horizontal; some models permit changing the position.


An electric drill with a non-conductive(usually plastic) housing, and with internal parts electrically isolated from anything conductive which can be touched by the operator.


Used almost interchangeably to designate (1) the power tool itself, or (2) a single bit to be used in the power tool. In this glossary, the power tool will generally be meant.

Drill Bit:

A tool intended to be rotated about its own axis in order to make a cylindrical hole in a workpiece. Common “twist” bits are cylindrical with helical grooves to carry away swarf, and have a pair of cutting edges at the leading face. MANY varieties exist, with differences in every conceivable feature.

Drill Motor:

Same as “Drill” in the sense of the power tool; may be regional usage.

Drill Press:

A device which guides and aligns a chuck relative to a table. Commonly, this is a complete dedicated unit. One form uses a portable electric drill as its power source, and provides a column, base, table and feed mechanism. It may also have stops for drilling blind holes. This second type will be most often used in this glossary. Click here for extended entry

Electric Drill:

A power tool using an electric motor to rotate a drill bit.


an impeller on the motor shaft, designed to move cooling air across parts which heat up due to electrical resistance, friction, etc. Slots or holes are provided in the housing to allow intake and exhaust of outside air.

Gears, Gearing:

The set of toothed wheels which reduce the RPM of the motor while increasing the torque.

Gear Case:

This is the part of the housing with the reduction gears. It may be separate from the motor housing, or all-in-one.


A feature attached to the body of the drill, or to the motor housing or gear case, for holding it, and directing the path of the tool. Common types include the pistol grip, the “D”-handle, the central handle, and a sort of inverted “U”, almost always at the back end of the housing.


The enclosure and structure of the drill, covering electrically live or moving components, providing alignment of gearing and bearings, holding lubricant, etc. On double-insulated drills, this is usually plastic; on older drills, it is metal.


Brand of chuck.

Keyless Chuck:

A chuck which can be tightened or loosened by hand. Most have two knurled sections, and require two hands to operate.


Brand of chuck


Brand of chuck.


The condition where the only loading on the motor is that of bearing friction, gear loading, windage (air resistance of the rotating parts), and lubrication losses.


a drill having a single handle, normally below the body, and at the rear.

Plain Bearings:

“Simple” bearings usually consisting of a soft metal or plastic in contact with shafts or other moving parts. Some are made from sintered metals (powdered metal solidified under high pressure and sometime s temperature). They are usually porous, and may be pre-lubricated by soaking in a lubricant. Plastic bearings may also incorporate lubricant, or be self-lubricating.


The two- or three-pronged unit which engages with an electrical outlet; on the end of the power cord.

Power Cord:

The cable connecting the plug to the power switch. Usually enters the handle of pistol-grip drills through a strain relief. It will have either two or three conductors, insulation around each, and may include a jacket surrounding all wires. Fillers to round out the shape, and fibers intended to carry any tensile loads, are commonly included within the jacket.

Pushbutton Switch:

A switch where the motion is axially along the actuator. The “One-Hand-Y” drill had one at the rear, to be operated by the thumb.


A shallow blind hole at the rear of the body, intended to locate the tool when put into a drill press, bench mount, or other fixture. Some portable attachments also utilize this feature.

Reversing Switch:

The separate switch controlling rotation direction on reversible or variable speed reversible drills.


Brand of chuck (company best known for plumbing tools, now makes many power tools).

Right-Angle Drill:

A drill with the axis of the chuck at 90° to that of the motor. This may be for use in close quarters, or to utilize worm gearing for low speed and high torque. Some models permit swiveling the axis to reach otherwise inaccessible locations.


Brand of chuck. Appears to be Rohm, but with the “M” written in three segments.


Brand of chuck.

Rolling-Element Bearing:

A bearing incorporating balls, rollers, or truncated cones of a hardened material rolling in raceways. These greatly re\duce friction, making the tool more efficient.

Rotation Lock:

A means to stop the chuck from rotating. Sometimes used to permit one hand to twist the ?


The Revolutions Per Minute of the chuck, usually given at no-load speed. The motor is usually geared down for greater torque.

Single Speed:

An electric drill with only “on/off” control; most are not reversible.

Slide Switch:

A power switch actuated by sliding the control element. On electric drills, this type is typically above a “D” handle and positioned for the thumb to move.

Strain Relief:

A sheath surrounding the first portion of the power cord where it emerges from the body of the drill. It reinforces the cord and limits bending to prevent damage.


Brand of chuck


The chips or shavings removed from the material being drilled.


The device controlling whether electrical power is provided to the motor of a drill. The most common form is like a trigger, but toggle-, slide-, and pushbutton switches have been used.

Toggle Switch:

A power switch actuated by sideways motion of the actuator. On electric drills, this may be enclosed within a “D”-handle, or at the front of a pistol grip, and moved up/down. At least on model put it on the side of the body, where it could be moved up/down by the thumb.


The twisting force imparted by the drill. For more, click here.


A switch actuator incorporated into the handle in such a way as to permit actuation by the index finger.

Trigger Lock:

A feature permitting the trigger to be kept in the “On” position without the need for continuous use of a finger. Most have a side button which is depressed after the drill is running; it disengages upon a second pull upon the trigger. Others use a button or pin at the bottom of the handle, or require a tilting motion of the trigger itself to engage. Still others had a wire bail which slipped over the trigger when pulled “On”.


An electric drill with two gear reductions available. Generally made obsolete by the introduction of the variable-speed drill.


A type of motor which will run on AC or DC.

Variable Speed, Variable Speed Reversible:

An electric drill with a means for controlling the rotation speed of the motor, usually electronically. Most can be run in reverse (using a separate reversing switch to control direction), and often can be mechanically set to a chosen speed, and kept there using a trigger lock or by finger pressure.


The rating for electrical potential, usually 110 to 120 Volts in the US, and 220 to 240 Volts in many other palaces. At least some drills were made for use on 32 Volts to work off of wind-power generators.