U.S. patent number RE38,778 [Application Number 09/110,145] was granted by the patent office on 2005-08-23 for magnetic bit holder and hand tool incorporating same.
This patent grant is currently assigned to Snap-on Incorporated. Invention is credited to Daniel M. Eggert, Daniel J. Garramone, Frank Mikic.
United States Patent |
RE38,778 |
Eggert , et al. |
August 23, 2005 |
Magnetic bit holder and hand tool incorporating same
Abstract
A hand tool has an elongated shank with a handle at one end and
a bit holder at the other end, the bit holder including a
cylindrical body having a distal end surface and an axis, the body
having an axial bore formed in the end surface of non-circular
transverse cross section and terminating at an inner end surface. A
neodymium permanent magnet is freely received in the bore and
retained against the inner end surface by a thin circular retainer,
formed of metal or plastic, which is interference-fitted in the
bore. Both flat, disk-like and concave, bowl-shaped retainers are
disclosed. A shock-absorbing cushion may be disposed between the
magnet and the inner end surface of the bore. A bit formed of
magnetizable material is mateably received in a socket portion of
the bore and retained in place by the magnet. The portion of the
bore receiving the magnet may have a different cross section from
the socket portion. The magnet may be disposed in an encapsulation
which interference fits in the bore.
Inventors: |
Eggert; Daniel M. (Kenosha,
WI), Mikic; Frank (late of Lake Geneva, WI), Garramone;
Daniel J. (Deerfield, IL) |
Assignee: |
Snap-on Incorporated (Pleasant
Prairie, WI)
|
Family
ID: |
23314109 |
Appl.
No.: |
09/110,145 |
Filed: |
July 2, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
335992 |
Nov 8, 1994 |
05577426 |
Nov 26, 1996 |
|
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Current U.S.
Class: |
81/439;
81/125 |
Current CPC
Class: |
B25B
15/02 (20130101); B25B 23/12 (20130101) |
Current International
Class: |
B25B
23/00 (20060101); B25B 023/00 () |
Field of
Search: |
;81/432-439,125
;279/128,9.04-9.1,102 ;269/8 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Meislin; Debra S
Attorney, Agent or Firm: Sayfarth Shaw LLP
Claims
We claim:
1. A bit holder comprising: a cylindrical body having a distal end
surface and an axis, said body having formed in said end surface an
axial bore terminating at an inner end surface, a permanent magnet
received in said bore and having an outer surface, and retaining
structure in contact with the outer surface of said magnet and
interference fitted in said bore to retain said magnet in said
bore, said bore having a portion of non-circular transverse cross
section outboard of said retaining structure defining a
bit-receiving socket, said retaining structure including a discrete
retaining member friction fitted in said bore outboard of said
magnet, said retaining member being generally bowl-shaped and
convex toward said magnet, said retaining member and said inner end
surface cooperating to retain said magnet therebetween.
2. The bit holder of claim 1, wherein said magnet is formed of
neodymium.
3. The bit holder of claim 1, wherein said magnet has a transverse
cross-sectional size smaller than the cross-sectional size of said
bore so as to be freely receivable in said bore.
4. The bit holder of claim 1, wherein said retaining structure is
formed of metal.
5. The bit holder of claim 1, wherein said retaining structure is
formed of plastic.
6. The bit holder of claim 1, and further comprising a cushioning
member discrete from said magnet and disposed between said magnet
and said inner end surface.
7. The bit holder of claim 1, wherein said portion of said bore
defining said socket comprises a counterbore having a
cross-sectional size larger than that of the remainder of said
bore.
8. The bit holder of claim 7, wherein said retaining structure is
disposed in said counterbore.
9. The bit holder of claim 1, wherein said bore has the same cross
section along its entire length.
10. In combination with the bit holder of claim 1, a bit having a
transverse cross section such as to be mateably receivable in said
socket in driven engagement with said body.
11. A hand tool comprising: an elongated shank having a handle end
and a working end and a longitudinal axis, a cylindrical body at
said working end having a distal end surface, said body having
formed in said end surface an axial bore terminating at an inner
end surface, a permanent magnet received in said bore and having an
outer surface, and retaining structure in contact with the outer
surface of said magnet and interference fitted in said bore to
retain said magnet in said bore, said bore having a portion
outboard of said retaining structure of non-circular transverse
cross section defining a bit-receiving socket, said retaining
structure including a discrete retaining member friction fitted in
said bore outboard of said magnet, said retaining member being
generally bowl-shaped and convex toward said magnet, said retaining
member and said inner end surface cooperating to retain said magnet
therebetween.
12. The hand tool of claim 11, wherein said magnet is formed of
neodymium.
13. The hand tool of claim 11, wherein said portion of said bore
defining said socket comprises a counterbore having a
cross-sectional size larger than that of the remainder of said
bore.
14. The hand tool of claim 11, wherein said bore has the same cross
section along its entire length..Iadd.
15. A bit holder comprising: a body having a distal end surface,
said body having a bore formed in said end surface, a magnet
received in said bore and having an outer surface, and a discrete
retaining member friction fitted in said bore outboard of said
magnet and substantially covering said outer surface of said magnet
to retain said magnet in said bore, said bore having a portion
outboard of said retaining member defining a bit-receiving
socket..Iaddend..Iadd.
16. The bit holder of claim 15, wherein said magnet is a permanent
magnet..Iaddend..Iadd.
17. The bit holder of claim 15, wherein the portion of said bore
outboard of said retaining member is non-circular in transverse
cross section..Iaddend..Iadd.
18. The bit holder of claim 15, wherein said retaining member is
generally bowl-shaped and convex toward said
magnet..Iaddend..Iadd.
19. The bit holder of claim 15, wherein said body has an axis of
rotation extending through said end surface, said bore being formed
axially in said end surface..Iaddend..Iadd.
20. The bit holder of claim 15, wherein said bore terminates at an
inner end surface, said retaining member cooperating with said
inner end surface to retain said magnet
therebetween..Iaddend..Iadd.
21. The bit holder of claim 15, wherein said retaining member is a
substantially circular disk..Iaddend..Iadd.
22. A bit holder comprising: a body having a distal end surface,
said body having a bore formed in said end surface, a magnet
received in said bore and having an outer surface, and a discrete
retaining member friction fitted in said bore outboard of said
magnet to retain said magnet in said bore, said retaining member
having a continuous outer periphery such that any two points on the
periphery can be joined by a straight line segment which does not
extend outside the periphery, said bore having a portion outboard
of said retaining member defining a bit-receiving socket..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to hand tools and, in particular, to
tools incorporating a bit holder for receiving interchangeable
bits, such as screwdriver bits or the like. The invention has
particular application to tools in which bits are magnetically
retained in a bit holder.
2. Description of the Prior Art
Typical current magnetic bit holders include a cylindrical body
having a socket formed axially in one end thereof for mateably
receiving an associated bit. The inner end surface of the socket
has further formed therein an axial hole of reduced cross section
receiving an associated magnet to retain the bit in place in the
socket. A suitable permanent magnet is press-fitted or crimped into
the magnet hole for magnetically retaining the associated bit in
place. The magnet is commonly formed of a material such as Alnico
and has considerable mass, typically being approximately one inch
long and approximately one-quarter inch in diameter.
Other permanent magnet materials, such as neodymium, have been
provided which can afford greater magnetic holding power with
significantly reduced magnet mass. However, neodymium magnets are
extremely brittle and cannot be press fit or crimped, nor can they
be impacted in use by a bit, since such handling may cause the
magnet to fracture and separate from the tool.
SUMMARY OF THE INVENTION
It is a general object of the invention to provide an improved
magnetic bit holder which avoids the disadvantages of prior bit
holders while affording additional structural and operating
advantages.
An important feature of the invention is the provision of a
magnetic bit holder which obviates the drilling of a separate hole
for retention of a permanent magnet.
A further feature of the invention is the provision of a bit holder
of the type set forth, which can effectively use a neodymium
magnet.
Yet another feature of the invention is the provision of a bit
holder of the type set forth which can effectively retain a
neodymium magnet in place, minimizing the risk of fracture thereof
and assuring adequate retention even in the event of fracture.
Yet another feature of the invention is the provision of a hand
tool incorporating a bit holder of the type set forth.
These and other features of the invention are attained by providing
a bit holder comprising: a cylindrical body having a distal end
surface and an axis, the body having formed in the end surface an
axial bore terminating at an inner end surface, a permanent magnet
received in the bore and having an outer surface, and retaining
structure in contact with the outer surface of the magnet and
interference fitted in the bore to retain the magnet in the bore,
the bore having a portion of non-circular transverse cross section
outboard of the retaining structure defining a bit-receiving
socket.
The invention consists of certain novel features and a combination
of parts hereinafter fully described, illustrated in the
accompanying drawings, and particularly pointed out in the appended
claims, it being understood that various changes in the details may
be made without departing from the spirit, or sacrificing any of
the advantages of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
For the purpose of facilitating an understanding of the invention,
there is illustrated in the accompanying drawings a preferred
embodiment thereof, from an inspection of which, when considered in
connection with the following description, the invention, its
construction and operation, and many of its advantages should be
readily understood and appreciated.
FIG. 1 a side elevational view of a hand tool incorporating a
magnetic bit holder in accordance with the present invention, shown
retaining an associated bit;
FIG. 2 is an enlarged fragmentary view in horizontal section taken
along the line 2--2 in FIG. 1, and illustrating a cushion member
for the permanent magnet and a bowl-shaped metal retainer
therefor;
FIG. 3 is a further enlarged view in vertical section taken along
the line 3--3 in FIG. 2;
FIG. 4 is a top plan view of a flat, disk-like, plastic magnet
retainer;
FIG. 5 is a sectional view taken along the line 5--5 in FIG. 4;
FIG. 6 is a view similar to FIG. 2 showing an alternative
embodiment of the present invention;
FIG. 7 is a view similar to FIG. 2 showing yet another embodiment
of the present invention utilizing an encapsulated magnet;
FIG. 8 is a sectional view of the encapsulated magnet of FIG. 7;
and
FIG. 9 is a view similar to FIG. 8 showing a partially-encapsulated
magnet.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is illustrated a hand tool 10 having an
elongated shank 11, provided at one end thereof with an enlarged
handle 12 and provided at the other end thereof with a
substantially cylindrical bit holder 20. The shank 11 and the bit
holder 20 are preferably of unitary, one-piece construction, being
formed of a suitable metal, while the handle 12 may be formed of
any desirable material, such as wood, plastic or the like. The
handle 12 may have an axial bore to receive the adjacent end of the
shank 11 or, alternately, may be formed around the handle end of
the shank 11, as by a suitable molding process, all in a known
manner.
Referring also to FIG. 2, the bit holder 20 includes a circularly
cylindrical body 21 having a distal end surface 22 in which is
formed an axial bore 23, which has a transverse cross-sectional
shape which is non-circular, such as polygonal. Preferably, the
bore 23 is hexagonal in transverse cross section. The bore 23
terminates at an inner end surface 24.
A permanent magnet 25 is freely received in the bore 23, the magnet
25 preferably being formed of a strong magnetic material, such as
neodymium. The magnet 25 is preferably cylindrical in shape, having
a diameter smaller than the across-sides width of the bore 23. It
will be appreciated that the size of the magnet 25 shown in the
drawing is simply for purposes of illustration and that the magnet
may actually be quite small and still provide sufficient holding
force to retain an associated bit.
In order to retain the magnet 25 in place, there is also provided a
retainer 26 which is in the shape of a flat, circular disk, and may
be formed of a suitable metal. The retainer 26 is dimensioned to be
interference-fitted in the bore 23 against the outer surface of the
magnet 25. Thus, it will be appreciated that the retainer 26 serves
to effectively retain the magnet 25 in place against the inner end
surface 24. The retainer 26 is as thin as possible, preferably
0.005 inch or less, so as to maximize the magnetic coupling force
between the permanent magnet 25 and the associated bit. A
shock-absorbing cushion 27, formed of rubber or other suitable
shock-absorbing material, may be provided between the magnet 25 and
the inner end surface 24 of the bore 23. This serves to cushion the
brittle neodymium magnet 25 against shock. While the cushion 27 is
preferably provided, it is not essential and could be dispensed
with.
The portion of the bore 23 outboard of the retainer 26 defines a
socket or cavity for receiving an associated bit 30. More
specifically, the bit 30 has a working end 31, which may be in the
nature of a screwdriver bit, such as a cross-tip bit, a flat blade
bit or the like, and also includes a hexagonal end 32 shaped and
dimensioned for mating engagement in the bore 23 for driven
engagement therewith. As can be seen in FIG. 2, the hex end 32 of
the bit 30 bottoms against the retainer 26 and is magnetically
retained in place therein by the magnetic holding force of the
permanent magnet 25.
It will be understood that, even in the event that the permanent
magnet 25 should fracture with use, the retainer 26 will
effectively serve to retain the magnet 25 in place and prevent
escape of any magnet parts from the bore 23. It will be also
understood that a significant aspect of the invention 0is that it
obviates the drilling of an additional magnet-retaining hole in the
body 21 of the bit holder 20, thereby reducing the fabrication
costs.
Referring now also to FIGS. 4 and 5, there is illustrated an
alternative form of retainer, generally designated by the numeral
35, which is a generally bowl-shaped, circular retainer, which is
preferably oriented in use with its convex side facing the magnet
25 and is also dimensioned to be press-fitted in the bore 23. The
retainer 35 is illustrated as being formed of a suitable plastic
material. It will be appreciated, however, that either of the
retainers 26 or 35 could be formed or either metal or plastic. The
bowl-shaped configuration of the retainer 26 also affords a certain
flexible resilience, which can provide an additional cushioning
effect to reduce the shock forces applied to the permanent magnet
25.
Referring to FIG. 6, there is illustrated an alternative bit holder
generally designated by the numeral 40, which is similar to the bit
holder 20, described above, except for the nature of the bore
therein. More specifically, the bit holder 40 has a cylindrical
body 41 in which is formed an axial bore 43 terminating at an inner
end surface 44. The bore 43 may have any desired cross-sectional
configuration, but is preferably circularly cylindrical. The bore
43 is provided with an enlarged cross section counterbore 45 which
is non-circular in transverse cross section, preferably being
hexagonal.
In this embodiment, the magnet 25 is dimensioned to fit freely in
the bore 43 and, again, the cushion 27 may or may not be provided.
The retainer 26 (or the retainer 35) is then mounted in the
counterbore 45 in the same manner as was described above in
connection with FIG. 2, for retaining the magnet 25 in place.
Referring now to FIG. 7, there is illustrated another embodiment of
the invention, utilizing an encapsulated magnet 50. More
specifically, the magnet 25 is completely surrounded with an
encapsulation 51. The thickness of the encapsulation 51 along the
side of the magnet 25 is such as to provide an interference fit in
the bore 23, so that the magnet may be retained in place without
the use of the retainers 26 or 35. The thickness of the
encapsulation 51 along the outer surface of the magnet 25 is such
as to provide the necessary protection of the magnet 25 from shock
as a result of contact with the bit 30. Also, it will be
appreciated that, in the event that the magnet 25 is fractured, the
encapsulation 51 will prevent the escape of any pieces of the
magnet 25.
In the embodiment illustrated in FIG. 7, the encapsulation of the
magnet is in the nature of a settable adhesive which may be
deposited in liquid form around the magnet 25 in the bore. Thus, a
thin layer of adhesive could first be deposited in the bore and the
magnet set thereon and then the remainder of the adhesive flowed
around the sides and outer surface of the magnet. Alternatively,
the magnet could be set on the end surface of the bore and then
adhesive flowed around the magnet in the manner described above.
After the adhesive has set, it serves not only to retain the magnet
in the bore 23 of the bit holder 20 or the bore 43 of the bit
holder 40, but would also provide a buffering protective layer
between the magnet and the associated bit 30.
While, in the embodiment of FIG. 7, the encapsulation of the magnet
is provided in situ in the bore, it will be appreciated that the
encapsulation could be provided before the magnet is inserted in
the bore of the bit holder. Referring to FIG. 8, there is
illustrated another embodiment of an encapsulated magnet 55,
wherein the magnet 25 is completely surrounded with an
encapsulation 56, which may be formed of any suitable material,
including plastic, rubber, brass or the like, but for purposes of
illustration is shown as having a metal encapsulation. The
dimensions of the encapsulation 56 may be similar to that of the
encapsulation 51 of FIG. 7 and for the same reasons. In this case,
the prefabricated encapsulated magnet 55 is press-fitted into the
bore 23, the encapsulation 56 protecting the magnet 25 from
fracture during the press-fitted insertion.
Referring to FIG. 9, there is an alternative embodiment of the
encapsulated magnet, generally designated by the numeral 60, which
utilizes encapsulation 61 covering only the outer and side surfaces
of the magnet 25. If desired, any of the magnets 50, 55 or 60 could
be used together with the cushion 27 between the magnet and the end
surface of the bore. Also, while the encapsulated magnet has been
illustrated as mounted in the bore 23 of the bit holder 20, it will
be appreciated that it could also be disposed in the bore 43 of the
bit holder 40.
From the foregoing, it can be seen that there has been provided an
improved bit holder and a hand tool incorporating same, which
afford the improved magnetic holding ability of a neodymium magnet,
while at the same time minimizing risk of fracture of the magnet,
and assuring retention of the magnet in place, even in the event of
fracture.
* * * * *