Dead blow hammer

How it works

A solid hammer head that strikes a hard object recoils. Kahlen’s 1952 patent explains that part of the kinetic energy of the blow is stored as distortion of the striking surface, like a compressed spring, and the release of that energy makes the hammer rebound. If a force equal and opposite to the stored energy acts at the moment the recoil would begin, the two cancel and the energy becomes heat.

The loose filler supplies that force. Kahlen says irregular hard particles in a chamber behind the face deliver not a single impact but a rapid succession of overlapping impacts, a longer impulse that begins while the head is still in contact with the work. Carmien’s 2001 patent describes the same behavior in a steel framing hammer: on impact the filler shifts and slides within a hollow canister, absorbing the impact force and counteracting rebound. A greater share of the kinetic energy then reaches the target.

Kahlen and Carmien both state the consequence for the user: the same work can be done with fewer blows or with a lighter head, and less strength and skill are needed to control the hammer after each blow. The effect does not depend on a soft face; Carmien notes that earlier nonrecoil hammers were generally limited to mallets with relatively soft faces and were ill-suited to framing, where a hardened steel head is wanted.

Anatomy

Head shell: Molded polymer or composite on most dead blow hammers; forged steel in Carmien’s framing hammer.
Cavity: A closed chamber behind the face, partly filled. Kahlen specifies a partial fill with free space; Carmien uses a hollow canister seated in the head.
Filler: Loose lead shot (Cook), steel pellets (Bergkvist) or steel shot (Carmien), or irregular hard particles (Kahlen). Snap-on describes a steel canister with free-flowing shot.
Face or tip: Urethane, rubber, plastic or steel.
Handle: Composite, fiberglass or steel; Snap-on’s composite shank runs from the head through the handle, and Cook’s hammer has a skeletal rod handle inside a molded resilient covering.

Variants

Steel-faced dead blow hammer: Hammers with a hardened steel head and a movable filler, described in Carmien’s 2001 patent for framing and similar work.
Ball-peen dead blow hammer: Snap-on’s 2005 HBBD series, 8 to 40 oz, with a polished steel peen and head over an internal steel shot canister.
Recoil-dampened workshop hammer: Bergkvist’s 1999 patent for Hultafors adds a rigid element in the handle and a counterweight to a particle-filled head to reduce recoil, rotation and vibration.
Bounce-resistant rubber mallet: Estwing’s Deadhead rubber mallets, in black and gray non-marring versions with hickory handles.

Specifications

Head weight · oz or lb: Snap-on’s ball-peen series runs from 8 to 40 oz.
Face diameter · in: Snap-on lists 1.00 to 1.75 in. for 8 to 40 oz.

Made to

ASME B107.400

Safety and care

Safety

Snap-on’s announcement warns users and bystanders to wear safety goggles.
Do not use one hammer to strike another hammer or other hard metal objects; a steel face or peen can chip (CCOHS).

Care

CCOHS advises discarding a hammer with a cracked or damaged head or a loose or damaged handle.

Tips

Use a lighter head for the same work
Kahlen says the prolonged impulse of the shot lets a lighter hammer be used for a given job than would otherwise be possible. Carmien makes the same point for a steel framing hammer.1 2
Choke up in tight spaces
Snap-on’s ball-peen dead blow hammers have a multi-position grip that lets the user choke up on the handle in tighter work areas, and a wide flare at the handle end that helps keep the hammer from slipping out of the hand.1
Look for non-sparking construction near flammables
Snap-on says the materials of its composite-handled hammers resist most shop chemicals and are non-sparking.1

History

Earliest documented

1944

Canada (West Vancouver, British Columbia)

Kahlen’s US Patent 2,604,914, issued in 1952, carries a Canadian application date of 13 May 1944 and a US filing of 9 January 1950, and describes a hammer head with a chamber of irregular hard particles directly behind the striking face. The patent says that three methods of preventing recoil were already known: a solid slug, a charge of round shot, or a charge of powder in a chamber behind the face, none of them very successful. The patent does not say who used those methods or when. A magazine article of January 1950 titled “‘No bounce’ Hammer Has Plastic Tips” is cited in a later patent; its construction is not known here.1 2

The dead blow hammer is a patent history before it is a catalog history. The earliest document located is Kahlen’s patent, which carries a Canadian date of 1944 and was issued in the United States in 1952. Kahlen treats the idea of a loose charge behind the striking face as already known and finds earlier forms unsuccessful: a solid slug delivers its own recoil, powder packs into a solid mass, and round shot has too little friction. His own proposal is irregular particles, whose friction and interlocking keep them from dispersing.

Later patents repeat the principle in new construction. Cook’s 1977 patent encases a hollow head of lead shot in a molded resilient covering, with a skeletal rod handle. Bergkvist’s 1999 patent, for a Swedish maker, lengthens the handle with a rigid element and a counterweight to reduce recoil, rotation and vibration. Carmien’s 2001 patent puts a canister of movable pellets into the socket of a hardened steel head. Carmien’s background describes the problem plainly: without a damping filler a hammer rebounds, and the worker needs more blows, a harder swing, or a heavier head.

The name is later than the principle. The patents located here call the tool a hammer head with rebound-preventing means, a non-rebound hammer, a nonrecoil hammer and, in Carmien, a deadblow hammer; Knight’s dictionary of the 1870s uses dead-stroke for a power hammer, which is a different thing. When the name for the hand tool first appeared has not been located.

Snap-on’s 2005 announcement carried the idea into a ball-peen hammer with a steel canister of shot.

In O*NET’s Tools Used table, dead blow hammers are named as examples for nine occupations, including millwrights and general maintenance and repair workers. No published test of rebound reduction, such as measured rebound heights or impulse durations, has been located; the evidence for the effect is the patent descriptions.

Timeline

1870s
Knight’s American Mechanical Dictionary defines a dead-stroke hammer as a power hammer that delivers its blow unaffected by the recoil of the shaft on which the ram is stocked; the term then named a machine, not a hand tool.1
1944
Kahlen files in Canada, on 13 May, for a hammer head with irregular particles in a chamber behind the face to prevent rebound.1
1950
Kahlen files in the United States on 9 January. A magazine article of January 1950 on a “no bounce” hammer with plastic tips is cited in a later patent.1 2
1952
US Patent 2,604,914 is issued to Kahlen of West Vancouver on 29 July.1
1977
Cook, assigned to C. E. S., Inc. of Indianapolis, is issued US 4,039,012 for a hollow cylindrical head filled with recoil-inhibiting pellets such as lead shot, with metal end caps and a resilient covering.1
1995
Bergkvist and others, for Hultafors AB of Sweden, file a Swedish priority application on 28 July for a hammer with a particle-filled cavity; US 5,916,338 is issued on 29 June 1999.1
2001
Carmien is issued US 6,234,048 (filed 2000) for a steel-headed hammer with a socket holding a canister of movable filler.1
2005
Snap-on announces its ball-peen dead blow hammer series on 18 July.1

Gaps in the record (5)

The origin of the term dead blow for the hand hammer, and the date of the first commercial dead blow hammer, have not been located.
Kahlen’s patent cites earlier slug, round-shot and powder hammers without naming makers; earlier patents cited by Cook and Bergkvist, including US 2,566,517 (Dicks, 1951), were not read. The 1950 magazine article is known only from a citation in Bergkvist’s patent.
Rebound-reduction claims by the makers have not been checked against any independent test, so buying is null.
Removed for sourcing: the NUPLA variants, tip-hardness and replace-only-the-tip tips, the NUPLA weight, tip-diameter and tip-material figures, the care item on replacing a worn tip, the non-sparking claim for NUPLA hammers, and the company’s 1938 founding and design claims, all of which cited the NUPLA catalog hosted on a distributor’s site (nafeco.com); nupla.com and archived copies could not be fetched from this machine.
Whether ASME B107.400 covers dead blow hammers has not been established; its text was not read, so the standard slug is unverified.