Rotary hammer

How it works

A rotary hammer pairs a drive with a striker. A 1975 Hilti patent describes the arrangement: in a cylinder an air cushion is provided between a driving piston and a striking piston. As the driving piston reciprocates, the air cushion makes the striking piston move axially and hit a tool held in a tool carrier. A second 1975 patent, assigned to Licentia, describes the same layout as a work piston connected to the gearing and a striker body that slides freely in the cylinder and is driven by the work piston through the interposed air cushion.

The striker is not fixed to the motor, so the blow is delivered by a free-flying mass. The Licentia patent describes the striker body as inserted into a spindle sleeve that the gearing rotates, which is how the bit turns while it is struck. The Hilti patent adds a provision for the case in which no tool is seated: openings in the cylinder let the air cushion escape when the striking piston moves forward past them, a ring catches the striking piston, and the cushion is restored when a tool is inserted.

Milwaukee’s manual for a 5/8-inch SDS Plus model states the result. The tool has two settings, rotation only and rotary hammering, chosen with a selector lever. It lists no-load speeds of 0 to 3,700 rpm and no-load blows of 0 to 4,400 per minute, and rates the tool for a 5/8-inch carbide-tipped percussion bit in concrete. The manual also describes a built-in, non-adjustable slip clutch that stops the bit from turning if it binds.

Anatomy

Mode selector: A lever that selects rotation only or rotary hammering on the Milwaukee model; Bosch says its SDS-plus hammers have multiple operating modes: rotary drilling, hammer drilling and chiseling.
Driving piston, air cushion and striking piston: The driving piston compresses the air that drives the striking piston, which hits the end of the bit (Schmuck 1975; Stiltz et al. 1975).
Spindle sleeve: Rotated by the gearing; carries the striker and the bit holder so that the bit turns while it is struck (Stiltz et al. 1975).
SDS or SDS Plus bit holder: A quick-change socket at the nose; the Milwaukee manual says to push the bit in until it locks and to use only accessories with SDS or SDS+ shanks.
Slip clutch: A built-in, non-adjustable clutch that stops the bit turning when it binds (Milwaukee manual). Bosch’s account of its 1932 hammer says it already had a safety clutch.
Side handle: Rotates to a chosen position and tightens by its grip; the manual says to always use it.
Depth gauge rod: Slides to set the drilling depth, measured from the tip of the bit to the tip of the rod.
Forward/reverse switch: Adjustable only when the trigger is not pulled; the manual says to wait for the motor to stop.

Variants

SDS-plus hammer: Bosch describes its SDS-plus hammers as compact tools for light-to-medium-duty work in concrete and masonry, with bit capacities from 3/4 to 1-1/4 inches, in corded and 18-volt cordless forms. The Milwaukee model read is rated for a 5/8-inch percussion bit.
SDS-max hammer: Bosch describes its SDS-max hammers as built for heavy-duty drilling and chiseling in concrete and masonry, with bit capacities from 1-9/16 to 2 inches, in corded and 18-volt cordless forms.
Cordless rotary hammer: Bosch says it launched the world’s first professional cordless hammer drill, the GBH 24 V, in 1984, and a trade report of 2007 says its first lithium-ion hammer, the GBH 36 V-LI, came in 2005.
Hammer drill: A related tool in which two toothed or cam discs produce the blows. It has its own entry.

Specifications

Supply · V AC: 120 (Milwaukee 5263-20 manual)Milwaukee manual; the model is listed at 5.5 A.
No-load speed · rpm: 0–3,700 (same model)Milwaukee manual.
No-load blows per minute · BPM: 0–4,400 (same model)Milwaukee manual.
Carbide-tipped percussion bit in concrete · in: 5/8 (same model)Milwaukee manual capacity table; one maker’s example, not a survey.
Twist drill capacity, rotation only · in: 1 in wood; 1/2 in steel (same model)Milwaukee manual.
Bit capacity range by shank system · in: SDS-plus 3/4 to 1-1/4; SDS-max 1-9/16 to 2 (Bosch US catalog lines)Bosch category pages; the range for one maker’s lines, not a survey.

Made to

IEC 62841-1
IEC 62841-2-6
UL 62841-2-6
DIN 8033

Safety and care

Safety

The Milwaukee manual instructs the user always to use a side handle, to brace or hold the tool securely, and to hold it with both hands to keep control.
The manual instructs the user to wear ear protectors, because exposure to noise can cause hearing loss, and to wear eye protection and a dust mask suited to the work.
The manual instructs the user to check the work area for hidden pipes and wires before drilling, and to cut embedded rebar only if doing so does not affect the integrity of the building, consulting a structural engineer if in doubt.
The manual warns that the dust from drilling can contain crystalline silica from bricks and cement, and advises respiratory protection or an OSHA-compliant dust extraction solution.
OSHA 29 CFR 1926.1153, Table 1, row (vii), specifies for handheld and stand-mounted drills, including impact and rotary hammer drills, a drill equipped with a commercially available shroud or cowling with a dust collection system. OSHA’s fact sheet adds that the vacuum must provide the airflow the tool maker recommends or more, the filter must be 99 percent efficient or better with a filter-cleaning mechanism, and a HEPA-filtered vacuum must be used to clean dust from the holes.
The manual instructs the user to start a long bit at low speed with the tip in contact with the work, because at higher speed a freely spinning bit is likely to bend, and to apply pressure only in line with the bit.

Care

Inspect the tool for undue noise, misalignment or binding of moving parts and breakage; the Milwaukee manual says to return the tool to a service facility for inspection after six months to one year, depending on use, and never to disassemble it.
Keep the vents clear of dust and the tool clean and dry. The manual says to use only mild soap and a damp cloth, because gasoline, turpentine, thinners, chlorinated solvents and ammonia cleaners harm plastics, and never to immerse the tool.

Tips

Match the mode to the material
The Milwaukee manual says to select the rotary hammer mode with high-speed carbide-tipped bits for masonry, and the drill-only mode for wood, composition materials, plastic and metal. Its capacity table gives 1 inch in wood and 1/2 inch in steel in drill-only mode.1
Set the hole depth with the rod
Loosen the depth gauge, slide the rod forward or back and tighten it. The manual says the drilling depth is the distance between the tip of the bit and the tip of the rod.1
Judge the pace by the dust
The manual says a smooth, even flow of dust indicates the proper drilling rate and that the bit should not spin in the hole without cutting. If speed falls in a large or deep hole, it says to pull the bit partway out while the tool runs to clear the dust.1
Let the slip clutch free a bound bit
If the bit binds, the built-in clutch stops it turning. The manual says to stop the tool, free the bit and begin again. Bosch’s account of its 1932 hammer says a safety clutch was already part of it.1 2
Grease the shank lightly and keep it clean
The manual says dirt may cause the bit to line up improperly, and that for best performance the bit should be properly sharpened and the shank lightly greased before use. A bit is inserted by aligning it with the locking elements and pushing it in until it locks.1

History

Earliest documented

1932 (Bosch’s account of its first electric hammer); 1967 (Hilti’s account of the first electro-pneumatic hammer drill)

Germany (Bosch); Schaan, Liechtenstein (Hilti)

Bosch’s timeline says its first hammer drill came to market in 1932 with a swirl impact mechanism, could drill and chisel, and was called the “Bosch hammer” on construction sites. A trade report of 2007 repeats the date and says it already had a safety clutch. Hilti’s history says the TE 17 of 1967 was the first electro-pneumatic hammer drill. The two companies describe different mechanisms, and neither claim has been matched to a patent of its date.1 2 3

The rotary hammer came from the demand for a portable tool that could drill and chisel concrete with a real striking blow. Bosch’s account places the first such electric hammer in 1932, with a striking mechanism for drilling and chiseling. Hilti’s account places the first electro-pneumatic hammer drill in 1967. The 1975 patents set out the electro-pneumatic arrangement in full: a driving piston, an air cushion and a striking piston, with the striker rotated along with the bit through a spindle sleeve.

The patents show where the design was being worked on. The Hilti patent deals with the idle case, when the striker would otherwise run without a tool to hit; it vents the cushion through openings in the cylinder and catches the striker with a ring until a tool is inserted. The Licentia patent describes a striker body that slides freely in the cylinder and is driven through the air cushion. The patents give German priority dates of 24 November 1971 for Hilti and 25 August 1973 for Licentia, and the US grants followed in late 1975.

The tool is now defined by its holder and its weight classes. Bosch says it introduced SDS-plus in 1975 for changing bits and chisels without a tool, and a 2-kilogram hammer in 1981. Bosch’s current catalog divides its hammers into SDS-plus lines for light-to-medium work with capacities up to 1-1/4 inches, and SDS-max lines for heavy work with capacities up to 2 inches. Its 1984 cordless model, and its 2003 vibration control, show how the form changed after the mechanism was settled. OSHA’s silica rule now lists rotary hammer drills among the tools that need a dust-collecting shroud for specified tasks.

Timeline

1932
Bosch says the first hammer drill comes onto the market, with a swirl impact mechanism, able to drill and chisel and soon called a “Bosch hammer.”1 2
1967
Hilti introduces the TE 17, which its history calls the first electro-pneumatic hammer drill.1
1971
Hilti’s Peter Schmuck claims German priority on 24 November for an electropneumatic hammer with an air cushion between a driving piston and a striking piston and a retaining ring for the striker when no tool is seated.1
1973
Licentia’s inventors claim German priority on 25 August for a hammer drill in which a work piston drives a freely sliding striker body through an air cushion.1
1975
Bosch’s SDS-plus tool-holder system for changing bits and chisels without a tool is introduced, according to a trade report on Bosch’s anniversary milestones.1
1975
US Patent 3,921,729 (Hilti, Schmuck) is granted on 25 November, and US Patent 3,929,195 (Licentia) on 30 December.1 2
1981
Bosch introduces what it calls the first 2-kilogram rotary hammer.1
1984
Bosch says it launches the world’s first professional cordless hammer drill, the GBH 24 V.1 2
2003
Bosch builds the first vibration control into a 5-kilogram hammer, according to the same trade report.1

Where the sources disagree

Which was the first rotary or electro-pneumatic hammer?

Bosch’s first electric hammer drill came to market in 1932 with a swirl impact mechanism, able to drill and chisel.1 2
Bosch Power Tools (company timeline); repeated by Industrieanzeiger in 2007
The Hilti TE 17 of 1967 was the first electro-pneumatic hammer drill.1
Hilti Corporation (company history)

Gaps in the record (7)

The mechanism of the 1932 Bosch hammer is not described in the sources read, so it is not known whether it used an air cushion.
No patent or catalog has been read for the Hilti TE 17 of 1967, and Hilti’s history gives no mechanism detail.
The development of the SDS shank, including any Hilti TE-C precedent, and the 18-millimeter SDS-max shank and its date are not sourced here; only Bosch’s 1975 SDS-plus date from a trade report is.
Shank dimensions and the line between a rotary hammer and a hammer drill are not given in the sources read.
Impact energy in joules is not given in the Milwaukee manual read, so it is not stated.
No independent published test of rotary hammers has been sourced, so buying is null.
The standard slugs (IEC 62841-2-6, UL 62841-2-6, DIN 8033) have not been read; they are inferred.