Hammer drill

How it works

The hammer drill is an ordinary drill whose spindle can also move back and forth. A 1960 patent describes the arrangement used in such machines: two discs, axially toothed or provided with cam-like surfaces, of which one stays fixed to the housing and the other turns with the drill spindle. When spring pressure or the pressure of the operator urges the discs together, the spindle disc rides over the teeth of the fixed disc and the spindle performs percussion-like movements. The patent says the frequency depends on the number of teeth passing over each other and on the speed of the spindle.

The Milwaukee hammer-drill manual states the result in its specifications. At the low speed range of up to 1,350 rpm the tool delivers 22,000 blows per minute, and at the high range of up to 2,500 rpm it delivers 40,000. A lever selects either drilling alone or hammer-drilling. The manual says that to engage the hammering mechanism the operator must maintain pressure on the bit, and that when pressure is released the hammering stops.

A 1970 Milwaukee patent describes the same two-ratchet principle in a current form. A fixed ratchet and a ratchet on the spindle are brought together by the operator’s pressure. A thrust bearing, locked in place by a ball-locked shift collar, holds the ratchets apart when the spindle is to turn without hammering. The patent says the ratcheting generates a lot of heat and places a plastic spacer of poor thermal conductivity between the ratchets and the motor casing.

Anatomy

Hammer/drill selector: A lever that selects drilling alone or hammer-drilling; marked with a drill symbol and a hammer symbol in the Milwaukee manual.
Ratchet or cam discs: A fixed toothed disc and a toothed disc on the spindle; they ride over each other under the operator’s pressure to produce the blows (Muthmann 1960; Schnettler 1970).
Thrust bearing and shift collar: Carries the operator’s pressure when the tool is set to drill only and keeps the ratchets out of engagement (Schnettler).
Chuck: A keyed chuck on the Milwaukee model; the manual says to tighten it in each of its three holes and to remove the key after each use.
Side handle: An auxiliary handle that clamps around the front of the tool and rotates to a chosen position; the manual says to use it always.
Depth gauge rod: A rod that slides in a clamp beside the chuck. The manual says the drilling depth is the distance between the tip of the bit and the tip of the rod.
Speed selector: Selects a low range of up to 1,350 rpm or a high range of up to 2,500 rpm on the Milwaukee model.
Forward/reverse lever: Adjustable only with the trigger released; the manual says to wait for the motor to stop.

Variants

Corded hammer drill: The form in the Milwaukee 120-volt manual, with a keyed chuck and a pistol grip; the patents of 1960 and 1970 describe tools driven by a conventional electric motor.
Cordless hammer drill: Bosch says it launched the world’s first professional cordless hammer drill, the GBH 24 V, in 1984, for installation work far from power sockets.
Adjustable-percussion drill: The 1960 Muthmann patent describes a percussion adjusting nut that varies the distance between the toothed discs so that the percussion amplitude runs from none to full while the drill is in service.
Electropneumatic hammer: FEIN describes its first electric pneumatic hammer as using an air-cushioned striking mechanism that converts the motor’s rotation into a linear strike. Bosch’s 1932 hammer drill is described by Bosch as using a swirl impact mechanism and as able to chisel. This entry treats them as related; the rotary hammer is a separate entry.

Specifications

Supply · V AC: 120 (Milwaukee 5378 manual)Milwaukee manual; the model draws 7.5 A.
Blows per minute · BPM: 22,000 at low speed; 40,000 at high speed (same model)Milwaukee manual.
No-load speed · rpm: 0–1,350 low; 0–2,500 high (same model)Milwaukee manual.
Maximum carbide-tipped percussion bit in concrete · in: 5/8 (same model)Milwaukee manual capacity table; one maker’s example, not a survey.
Chuck capacity · in: 1/2 (the tool is sold as a 1/2-inch hammer-drill)Milwaukee manual title.

Made to

IEC 62841-1
IEC 62841-2-1
UL 62841-2-1

Safety and care

Safety

The Milwaukee manual instructs the user always to use the side handle, to brace or hold securely, and to hold the tool securely with both handles and keep control.
The manual instructs the user to wear ear protectors, because the hammering can cause hearing loss, and to wear a dust mask, safety glasses and other protective equipment suited to the work.
The manual warns that dust from drilling can contain crystalline silica from brick, cement and masonry, lead from paint and other chemicals, and advises ventilation and approved dust masks.
OSHA 29 CFR 1926.1153, Table 1, specifies for handheld and stand-mounted drills, including impact and rotary hammer drills, a drill equipped with a commercially available shroud or cowling with dust collection, for tasks that expose workers to respirable crystalline silica.
The manual warns against drilling through steel reinforcing rods and against using water to settle dust or cool the bit, because both damage the carbide.
The manual instructs the user to use hammer-drilling only in forward rotation, and not to use bits larger than the tool’s rated capacity because gear damage or motor overloading may result.
OSHA 29 CFR 1926.302 requires electric power tools to be double-insulated or grounded.

Care

Before use, inspect the tool, cord and any extension cord for damage and check for loose screws, binding and broken parts (Milwaukee manual). Under normal conditions relubrication is not necessary until the motor brushes need replacing; after six months to a year the manual advises returning the tool for lubrication, brush inspection and replacement, mechanical inspection and cleaning, and electrical inspection.
Keep the bit shank and the chuck jaws clean, because the manual says dirt may cause the bit to line up improperly, and use properly sharpened bits for best performance.

Tips

Hammer only while you press
The hammering engages under the pressure of the operator on the bit and stops when that pressure is released, according to the Milwaukee manual. The ratchet principle in the Schnettler patent works the same way: the operator’s pressure brings the two ratchets together.1 2
Use the drill setting for wood and metal and the hammer setting for masonry
The manual says to select the drill mode for wood, composition materials, plastic and metal, and the hammer-drill mode with high speed carbide-tipped bits for masonry. Soft masonry such as cinder block requires little pressure and concrete requires more.1
Set the depth with the rod
Press in the clamping lever, slide the depth gauge rod until it is set, and release the lever. The manual says the drilling depth is the distance between the tip of the bit and the tip of the rod, so the hole stops at the same depth each time.1
Read the dust to judge the pace
A smooth, even flow of dust indicates the proper drilling rate, and the bit should not be allowed to spin in the hole without cutting. If speed drops in a deep hole the manual says to pull the bit partly out while the tool is running to clear the dust.1
Choose the speed range before drilling
The speed selector can be changed at a complete stop or while running under no load. Position 1 gives up to 1,350 rpm with 22,000 blows per minute and position 2 gives up to 2,500 rpm with 40,000.1
Count on the cam or ratchet, not the motor, to set the blow rate
Muthmann’s patent says the frequency of the blows depends on the number of teeth passing over each other and on the spindle speed. The same drill therefore strikes faster at the higher speed, as the manual’s figures of 22,000 and 40,000 blows per minute show.1 2

History

Earliest documented

1932 (Bosch’s account of the first hammer drill); earlier percussion drills with toothed discs are described in a patent of 1957

Germany (Bosch, Stuttgart area; Muthmann patent, Berlin)

Bosch’s timeline says the first hammer drill came onto the market in 1932, used on construction sites, and could drill and chisel; its swirl impact mechanism proved itself in continuous use, and the tool was soon called a “Bosch hammer.” A 1957 patent application by Dieter Muthmann of Berlin states that percussion drills for walls and masonry were already needed in construction and describes the earlier arrangement of two toothed discs. FEIN’s history also describes an electric pneumatic hammer with an air-cushioned striking mechanism but does not give a date in the text read. The first-hammer-drill claims are the companies’ own and have not been checked against a patent.1 2 3

The hammer drill added a striking action to a rotating drill so that hard masonry could be bored without hand sledging. Muthmann’s application of 1957 states the need: percussion drills were wanted to pass through walls, masonry and door posts in the shortest possible time to lay gas, water and electric lines. It describes machines in which the spindle receives axial percussion movements while it turns, produced by two toothed or cam-surfaced discs, one stationary and one turning with the spindle, pressed together by a spring or by the operator.

The sources do not agree on who made the first one. Bosch says the first hammer drill reached the market in 1932 and calls it the world’s first electric hammer drill of its type used on construction sites. FEIN describes the first electric pneumatic hammer and its air-cushioned striking mechanism, and the text read does not date it. Vintage Machinery dates a small Milwaukee electric hammer for concrete and masonry to 1934. The mechanisms may not be the same, since Bosch calls its own a swirl impact mechanism and FEIN describes an air cushion, and no source read explains how the 1932 Bosch mechanism works. The question is set out under disputed.

The later development was in the details of the ratchet type. The Schnettler patent of 1970 lists the faults it sets out to correct in earlier ratchet drills: adjustment that was relatively slow and not positive, separate and expensive components such as a splined coupling to allow the spindle to slide, and no insulation of the ratchets from the motor and handle against the heat that ratcheting generates. Its answer was a quick shift collar locking balls, a spindle gear that slides along a long pinion, and a plastic spacer. The patent is the source of the account of what it replaced; no independent history of those changes was found.

The tool is now defined by its limits as much as its action. The Milwaukee manual rates a 1/2-inch model for a 5/8-inch carbide-tipped percussion bit in concrete at up to 40,000 blows per minute, tells the user to stop short of steel reinforcing rods, and requires a side handle and hearing protection. OSHA’s silica rule lists drills, including impact and rotary hammer drills, among the tools that need a dust-collecting shroud or cowling for specified tasks. Bosch’s 1984 cordless model shows the form moving to battery power. The larger rotary hammer, which strikes with a different mechanism, has its own entry.

Timeline

1932
Bosch says the first hammer drill comes onto the market, with a swirl impact mechanism, usable for drilling and chiseling on construction sites and soon called the “Bosch hammer.”1
1934
According to Vintage Machinery, the Milwaukee Electric Tool company introduces a small electric hammer for drilling holes in concrete and masonry.1
1957
Dieter Muthmann of Berlin files a patent application on 24 January for a percussion drill with an adjusting nut that varies the spacing of two toothed discs. The application says percussion drills of the toothed-disc type were needed to drill through walls and masonry quickly to lay gas, water and electric conduits.1
1960
US Patent 2,942,852 is granted to Muthmann on 28 June.1
1968
Jerome L. Schnettler files a patent application on 4 September for a Milwaukee Electric Tool hammer drill with a ball-locked shift collar and a heat-insulating spacer.1
1970
US Patent 3,511,321 is granted to Schnettler on 12 May. It names two earlier patents, 2,942,852 and 3,119,274, as the most pertinent prior art, both with a fixed ratchet and a rotating ratchet.1
1984
Bosch says it launches the world’s first professional cordless hammer drill, the GBH 24 V.1

Where the sources disagree

Which was the first hammer drill, and who made it?

Bosch’s first hammer drill came onto the market in 1932, with a swirl impact mechanism, and was soon called a “Bosch hammer.”1
Bosch Power Tools (company timeline)
FEIN built the first electric pneumatic hammer, with an air-cushioned striking mechanism; the text read gives no date.1
FEIN (company history)
Milwaukee introduced a small electric hammer for drilling holes in concrete and masonry in 1934.1
Vintage Machinery (secondary account)

Gaps in the record (8)

The Bosch 1932 and FEIN hammers have not been matched to patents, and FEIN’s history text read gives no date for its hammer; later summaries that date it to 1914 were not read at source.
The mechanism of the 1932 Bosch hammer drill is not described in the sources read.
The 1934 Milwaukee hammer is known only from Vintage Machinery, and no catalog or patent has been read.
Patent 3,119,274, named as prior art in the Schnettler patent, was not read for its date or assignee.
The date and origin of the SDS-type bit holder, and the line between a hammer drill and a rotary hammer, are not sourced here.
No independent published test of hammer drills has been sourced, so buying is null.
IEC 62841-2-1 and UL 62841-2-1 have not been read; the standard slugs are inferred.
The specs rest on one maker’s manual and are not a survey.