US3154851A

US3154851A - Electric shaver

Info

Publication number: US3154851A
Application number: US213219A
Authority: US
Inventors: Carl E Erickson
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-07-30
Filing date: 1962-07-30
Publication date: 1964-11-03
Anticipated expiration: 1981-11-03

Description

Nov. 3, 1964 c. E. ERICKSON 3,154,351

ELECTRIC SHAVER Filed July 30, 1962 3 Sheets-Sheet 1 if 4- INVENTOR.

BYgm a ATTORNEY,

Nov. 3, 1964 c. E. ERICKSON 3,154,851

ELECTRIC SHAVER Filed July 30, 1962 3 Sheets-Sheet 2 INVENTOR. Car/ 4 ff/C/YJOH BY 0M 4M ATTORNEY.

Nov. 3, 1964 c. E. ERICKSON 3,154,851

ELECTRIC SHAVER Filed July 30, 1962 3 Sheets-Sheet 3 INVENTOR. 60// f. 5/7 cksan BYgmq/x ATTORNEY United States Patent 3,154,851 ELECTREQ SHAVER Carl E. Erickson, 678 tlarroll Drive, Moraga, Quit.

' Filed .luly 3t), 1962, Ser. No. 213, l9

15 Claims. (til. 3il=-4l.5)

This invention relates to electric shavers. The main objects of this invention are:

First, to provide an electric shaver which is easy to manipulate and is highly eflicient.

Second, to provide an electric shaver which includes a blade unit comprising a driven shaft and a plurality of axially spaced parallel disk-like blades of the same size and shape fixedly mounted on the shaft for rotation therewith.

Third, to provide a rotatably driven blade unit which comprises relatively thin disk-like blades of the same shape and which are positioned so that they have a reverse stroke or movement relative to the face or" the shaver on each rotation of the unit.

Fourth, to provide a blade unit having these features in which the blade supporting shaft is tubular and constitutes a collector, there being inlets thereto between the several blades, and which may be cleaned without removal of the blade unit from the body member.

Fifth, to provide a shaver which includes the rotatably driven blade unit and an electric motor which is disposed with its rotor in parallel relation to the axis of the blade urit, and has driving connection thereto.

Sixth, to provide a shaver having these features in which the housing or body member provides a handle which may be conveniently and effectively grasped for manipulation of the shaver.

Objects relating to details and economies of the invention will appear from the description to follow. The invention is defined and pointed out in the claims.

A preferred embodiment of the invention is illustrated in the accompanying drawing in which:

FIG. 1 is a side view of a shaver embodying my invention.

FIG. 2 is an end view thereof.

FIG. 3 is a longitudinal section on a line corresponding to line 33 of FIG. 2.

FIG. 4 is a transverse section on a line corresponding to broken line 4-4 of FIG. 3.

FIG. 5 is an enlarged side elevational view of the blade unit, one position of the blades being indicated by full lines and a second position of some of the blades being indicated by dotted lines.

FIG. 6 is an enlarged fragmentary view on a line corresponding to line 6-6 of FIG. 5.

FIG. 7 is a perspective view of a fragmentary portion of the shaft, one of the blades and one of the blade supporting collars.

FIG. 8 is a fragmentary side view illustrating the assembled relation of the parts shown in FIG. 7.

In the accompanying drawing, some of the parts or elements are shown mainly conventionally as the details thereof may be varied, particularly in the matter of design and proportioning. However, it should be understood that the drawings do illustrate a practical and desirable embodiment of my invention except in the matter of size, it being deemed impractical to illustrate parts in commercial dimensions and such dimensions may be varied.

In the accompanying drawing, a housing designated generally by the numeral 1 comprises a pair of complementary members 2 which are substantial duplicates so far as desigi is concerned and they are desirably formed of molded plastic material.

These housing members have forwardly projecting laterally spaced flange-like portions 3 and opposed inwardly facing complementary transversely curved portions 4 which provide a chamber 5 of curved cross section, the purpose of which will appear as the description proceeds.

These housing members have inwardly curved outer side portions 6 merging into the outwardly curved outer or rear edge portion 7 and this provides an effective handhold or handpiece.

These body members have complementary inwardly projecting flange-like portions 8 and 9 having arcuately curved outer peripheral or edge portions 111) on which the fixed cutter and shield unit 14) is supportedly mounted. In this embodiment the unit it; is fixedly secured upon these flange-like portions 8 and 9 of the housing member by the screws conventionally illustrated at 11. The two housing members are secured together'by the bolts 12.

The fixed cutter and shield unit 10 is of curved cross section and'it extends transversely of the housing and comprises a pluralityof axially spaced spirally disposed slot-like openings 13 and a plurality of closely spaced apertures 14 between these slot-like openings. The edges of the slots 13 in the member it are desirably serrated as is indicated at 15.

As stated, no attempt was made to illustrate the slots 13 and the apertures 14 in use proportions and it should be understood that they may be substantially varied in size and arrangement. The fixed cutter and shield unit illustrated is however highly desirable particularly in combination with the cooperating blade unit of my invention which comprises a tubular shaft 16 rotatably mounted in ball bearings 17 which are supportedly mounted in openings 18 provided therefor in the flangelilze portions 8 and 9 of the housing member. A plurality of disk-like blades 19 are fixedly mounted on the shaft 16 in inclined relation to its axis and in laterally spaced relation to each other. These blades 19 are oval or slightly out of round in shape as is shown in FIG. 7. They are sleeved upon the shaft 15 and are fixedly supported thereon, desirably by means of the supporting collars 2t and 21, the supporting collars 28 being arranged between the blades, and the collars 21 at the outer side of the end blades, see FIGS. 3, '5 and 6.

As illustrated in FIGS. 7 and 8, the shaft 16 is provided with a longitudinal rib 22 and the blades 19 have notches 23 adapted to receive the rib 22 which insures that the blades are rotated with the shaft.

The blade spacing the collars 26 also has notches 24 therein which receive the ribs so that they are rotated with the shaft and with the blades as a unit. These collars 243 in the embodiment illustrated have opposed notches 24 so that they can be selectively positioned as illustrated in FIG. 8. With this arrangement, the several blades are all in the same co-operating relation to the relatively fixed shield and cutter unit it? and as the shaft is rotated, the cutting edge of each blade has a rotative and also laterally sweeping movement relative to the fixed cutter and shield 19 and that movement is indicated by dotted lines in FIG. 5 and all of the blades have the same movement. This is a compound movement and results in a highly effective shearing action between the fixed cutter unit and the rotating blade unit. It also results in a complete shaving action from end to end of the fixed cutter and shield unit 10.

This compound cutting movement of the blades is highly eificient and does not result in excessive wear on the cutting edges of the blade which are continuous and the blades cannot become deflected or displaced in use.

The blade supporting collars are mounted on the shaft between the blade and at the outer sides of the end blades and have inclined blade engaging ends which eifectively.

support the blades in their inclinedrelation to the axis the shaft. The blades are further connected to the shaft by the tubular conduits which are disposed through holes 26 provided therefor in the collars and Which engage the holes 27 in the shaft, see FIG. 6.

These conduits desirably project outwardly from the collars and are provided with blade-like portions 28 on their projecting ends, see FIGS.'3, 6 and Z.' With this arrangement, the blade unit produces a suction current of air and the severed whiskers or beard particles are drawn into the tubular cutter shaft which in the embodiment i1lustrated,'is provided with foraminate end closures 29 removably mounted in the ends of the shaft. See FIG. 3. With this arrangement, after use the closure members 29 are removed, the collected material can be brushed out of the tubular shaft.

In the embodiment illustrated a special form or design of electric motor 130 is provided, this comprising an elongated tubular housing 30 in which the fixed stator element '31 is mounted, the rotor element 32 including a shaft 33 which is rotatably mounted in bearings 34 pro,- vided therefor in the end member 35 of the housing. The electrical connections are conventionally illustrated at 361. The shaft 33 is provided with a gear 341 which is connected to the gear 35 on the blade unit by means of

gears

36 and 37 which are supported on spindle bearings 38 projecting inwardly from the supporting plate 3? which is secured to the housing members 2 by means of screws =conventionally illustrated at 40. The housing members are chambered or recessed at 41 to receive these gears.

' With this arrangement, all movable parts are eifectively housed and protected and the driven blades are shaped and mounted so that they have a lateral oscillating movement or strokes relative to the fixed cutter and shield unit and they are guarded so that they cannot injure the skin of the user and they are housed and supported so that they cannot be dulled or injured in the event the shaver is laid or held upon a surface with the motor running. It will be understood that the rotary element is driven at high speed in use.

I have illustrated and described my invention vin a highly practical embodiment thereof. As stated, some of the parts are shown mainly in conventional form and I have not illustrated or described various possible modifications or embodiments as it is believed this disclosure will enable those skilled in the art to embody or adapt my invention as may be desired.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent is:

1. In a razor, a housing of generally rectangular form and comprising a pair of complementary housing members disposed side by side and having forwardly projecting laterally spaced flanges provided with curved edge portions, 'said housing members having opposed complementary curved portions in their inner sides extending longitudinally thereof and providing a chamber of curved cross section extending transversely of said housing, said housing members having merging curved rear edge portions and inwardly curved side portions merging into said curved rear edge portion providing a handpiece,

ing laterally spaced flanges providedwith curved edge flanges and having a plurality of axially spaced spirally disposed slots therein and a plurality of apertures in the portions thereof betweenv the slots and at theouter sides of the end slots, a blade unit comprising a tubular shaft rotatably mounted on said flanges of said body member and opening therethrough, a plurality ,of oval disk-like blades mounted on'said shaft in inclined relation to. its axis and in parallel relation to each other and in coacting relation'to said cutter and shield unit," blade supporting collars mounted on said shaft between the blades and portions, said housing members having opposed cornplementary curved portions in their inner sides extending longitudinally thereof and providing a chamber of curved cross section extending transversely of said housing, a fixed cutter and shield unit of curved cross section supportedly mounted on and extending between said flanges and having a plurality of axially spaced spirally disposed slots therein and a plurality of apertures in the portions thereof between the slots and at the outer sides of the end slots, a blade unit comprising'a tubular shaft rotatably mounted on said flanges of said body member and opening therethrough, a plurality of oval disk-like blades mounted on said shaft in inclined relation to its axis and in parallel relation to each other and in coacting relation to said cutter and shield unit, blade supporting collars mounted on said shaft between the blades and at the outer sides of the outer blades and having inclined ends in axial thrust supporting engagement with inner portions of said blades, said shaft and collars having registering openings therein between adjacent blades and at the outer sides of the outer blades, a motor mounted in said chamber in said housing and including a rotor provided with a shaft disposed transversely of the housing, and gear connections for said motor shaft to said blade shaft disposed within said housing.

3. In a razor, a housing of generally rectangular form plementary curved portions in their inner sides extending longitudinally thereof and providing a chamber of curved cross section extending transversely of said housing, a fixed cutter and shield unit of curved cross section supportedly mounted on and extending between said flanges and having a plurality of axially spaced spirally disposed slots therein and a plurality of apertures in the portions thereof between the slots and at the outer sides of the end slots, a blade unit comprising a tubular shaft rotatably mounted on said flanges of said body member and opening therethrough, a plurality of oval disk-like blades mounted on said shaft in inclined relation to its axis and in parallel relation to each other and in coacting relation to said cutter and shield unit, blade supporting collars mounted on said shaft between the blades and at the outer sides of the outer blades and having inclined ends in axial thrust supporting engagement with inner portions of said blades, said shaft and collars having registering openings therein between adjacent blades and at the outer sides of the outer blades, conduits mounted in said openings in said shaft and, collars and having pick up portions projecting from said collars, foraminate closures for the ends of said blade unit shaft removably mounted on said housing, a motor mounted in said chamber in said housing and including a rotor provided with a shaft disposed transversely of the housing, and gear connections for said motor shaft to said blade shaft disposed within said housing.

4. In a razor, a housing of generally rectangular form having forwardly projecting laterally spaced flanges, said housing also having a curved rearedge and inwardly curved side portions merging into said curved'r'ear edge providing arhandpiece portion which as a chamber. there;

in, a foraminate fixed cutter and shieldunit of curved.

cross sectionextending between said flanges, a blade unit comprising a tubular shaft rotatably mounted on said flanges of said body member and opening therethrough, a plurality of disk-like blades mounted on said shaft in inclined relation to its axis and in laterally spaced parallel relation to each other and in coacting relation to said cutter and shield unit, blade supporting collars mounted on said shaft between the blades and at the outer sides of the outer blades and having inclined ends in axial thrust supporting engagement with inner portions of said blades, said shaft and collars having registering openings therein between adjacent blades and at the outer sides of the outer blades, conduits mounted in said openings in said shaft and collars and having pick-up portions projecting from said collars, a removable foraminate closure for one end of said tubular blade unit shaft, a motor mounted in said chamber in said housing and including a rotor provided with a shaft disposed transversely of the housing, and driving connections for said motor shaft to said blade shaft disposed within said housing.

5. in a razor, a housing having forwardly projecting laterally spaced flanges, a foraminate fixed cutter and shield unit of curved cross section extending between said flanges, a blade unit comprising a tubular shaft rotatably mounted on said flanges of said body member and opening therethrough, a plurality of disk-like blades mounted on said shaft in inclined relation to its axis and in laterally spaced para l relation to each other and in coacting relation to said cutter and shield unit, blades supporting collars mounted on said shaft between the blades and at the outer sides of the outer blades and having inclined ends in axial thrust supporting engagement with inner portions of said blades, said shaft and collars having registering openings therein between adjacent blades and at the outer sides of the outer blades, conduits mounted in said openings in said shaft and collars and having pick-up portions projecting from said collars, a removable foraminate closure for one end of said tubular blade unit shaft, a motor mounted in said chamber in said housing and including a rotor provided with a shaft disposed transversely of the housing, and driving connections for said motor shaft to said blade shaft disposed within said housing.

6. in a razor, a housing of generally rectangular form having forwardly projecting laterally spaced flanges, said housing also having a curved inner edge and inwardly curved side portions merging into said curved inner edge portion providing a handpiece portion which has a chamoer therein, a foraminate fixed cutter and shield unit of curved cross section extending between said flanges, a blade unit comprising a tubular shaft rotatably mounted on said flanges of said housing and opening therethrough, a plurality of oval disk-lilac blades mounted on said shaft in inclined relation to its axis and in laterally spaced parallel relation to each other and in coacting relation to said cutter and shield unit, said blades having continuous peripheral shearing edges and having their major diameters incline-d longitudinally of said shaft in a common plane passed through the shaft, said major diameters being of such a length that when multipled by the cosine of the angle or" inclination of the blades gives a dimension greater than the spacing between adjacent blades measured along the axis of said shaft so that the sweep of the ends of a major diameter of one blade laterally across said cutter and slu'eld unit overlaps the sweep of the opposite ends or" adjacent blades longitudinally of said cutter and shield unit, a motor mounted in said housing, and driving connections for said motor to said blade shaft disposed within said housing.

7. in a razor, a housing of generally rectangular form and comprising a pair of complementary housing members disposed side by side and having inwardly pr jecting laterally spaced flanges provided with curved edge portions, said housing members having merging curved rear edge portions and inwardly curved side portions merging into said curved rear edge portion providing a handpiece,

a fixed cutter and shield unit of curved cross section supportedly mounted on and extending between said flanges and having a plurality of axially spaced spirally disposed slots therein and a plurality of apertures in the portions thereof between the slots and at the outer sides of the end slots, a blade unit comprising a tubular shaft rotatably mounted on said flanges of said body member and opening therethrough, a plurality of disk-like blades mounted on said shaft in inclined relation to its axis and in spaced parallel relation to ecah other and in coacting relation to said cutter and shield unit, said shaft having inlet openings between said blades, a foraminate closure for one end of said blade unit shaft removably mounted on said housing, a motor mounted in said housing and including a rotor provided with a shaft disposed transversely of the housing, and driving connections for said motor shaft to said blade shaft disposed within said housing.

8. in a razor, a housing, a nxed cutter and shield unit of C11; ed cross section supportedly mounted on said housing, a blade unit compirsing a tubular shaft rotatably mounted in said housing and opening therethrough, a plurality of oval disk-like blades mounted on said shaft in inclined relation to its axis and in spaced parallel relation to each other and in coacting relation to said cutter and shield unit, said blades having continuous peripheral shearing edges and having their major diameters inclined longitudinally of said shaft in a common plane passed hrough the shaft, said major diameters being of such a length that when multipled by the cosin of the angle of inclination of the blades gives a dimension greater than the spacing between adjacent blades measured along the axis of said shaft so that the sweep of the ends of a major diameter of one blade laterally across said cutter and shield unit overlaps the sweep of the opposite ends of adjacent blades longitudinally of said cutter and shield unit, said shaft having inlet openings between said blades, a foraminate closure for one one of said blade unit shaft removably mounted on said housing, a motor mounted in said housing and including a rotor provided with a shaft disposed transversely of the housing, and driving connections for said motor shaft to said blade shaft disposed within said housing.

9. in a razor, a housing of generally rectangular form and comprising a pair of complementary housing members disposed side by side and having inwardly projecting laterally spaced flanges provided with curved edge portions, said housing members having merging curved rear edge portions and inwardly curved side portions merging into said curved rear edge portion providing a handpiece, a fixed cutter and shield unit of curved cross section supported-1y mounted on and extending between said flanges and having a plurality of axially spaced spirally disposed slots therein and a plurality of apertures in the portions thereof between the slots and at the outer sides of the end slots, a blade unit comprising a tubular shaft rotatably mounted on said flanges of said housing members and opening therethrough, a plurality of oval disk-like blades mounted on said shaft in inclined relation to its axis and spaced parallel relation to each other and in coacting relation to said cutter and shield unit, said blades having continuous peripheral shearing edges and having their major diameters inclined longitudinally of said shaft in a common plane passed through the shaft, said major diameters being of such a length that when multipled by the cosine of the angle of inclination of the blades gives a dimension greater than the spacing between adjacent blades measured along the axis of said shaft so that the sweep of the ends of a major diameter of one blade laterally across said cutter and shield unit overlaps the sweep of the opposite ends of adjacent blades longitudinally of said cutter and shield unit, a motor mounted in said housing and including a rotor provided with a shaft disposed transversely of the housing, and driving 7 connections for said motor shaft to said blade shaft disposed within said housing.

10. In a razor, a housing, a fixed cutter and shield unit of curved cross section supportedly mounted on said housing, a blade unit comprising a tubular shaft rotatably mounted in said housing and opening therethrough, a plurality of oval disk-like blades mounted on said shaft in inclined relation to its axis and in spaced parallel relation to each other and in coacting relation to said cutter and shield unit, said blades having continuous peripheral shearing edges and having their major diameters inclined longitudinally of said shaft in a common plane passed through the shaft, said major diameters being of such a length that when multipled by the cosine of the angle of inclination of the blades gives a dimension greater than the spacing between adjacent blades measured along the axis of said shaft so that the sweep of the ends of a major diameter of one blade laterally across said cutter and shield unit overlaps the sweep of the opposite ends of adjacent blades longitudinally of said cutter and shield unit, a motor mounted in said housing and including a rotor provided with a shaft disposed transversely of the housing, and driving connections for said motor shaft to said blade shaft disposed within said housing.

11. In a razor, a housing constituting a handpiece and having forwardly projecting laterally spaced support members thereon, a foraminate fixed cutter and shield unit of curved cross section supportedly mounted on said support members and having a plurality of axially spaced spirally disposed slots therein and a plurality of apertures in the portion between the slots thereof, a blade unit comprising a shaft rotatably mounted in said housing and provided 7 with a plurality of oval disk-like blades mounted on the shaft in inclined relation to its axis and in spaced parallel relation to each other and in coacting relation to said cutter and shield unit, said blades having continuous peripheral shearing edges and having their major diameters inclined longitudinally of said shaft in a common plane passed through the shaft, said major diameters being of such a length that when multipled by the cosine of the angle of inclination of the blades gives a dimension greater than the spacing between adjacent blades measured along the axis of said shaft so that the sweep of the ends of a major diameter of one blade laterally across said cutter and shield unit overlaps the sweep of the opposite ends of adjacent blades longitudinally of said cutter and shield unit, and means for driving said blade unit shaft including an electrically powered motor disposed within said housing and having driving connections to said shaft.

12. In a razor, a housing constituting a handpiece, a foraminate fixed cutter and shield unit of curved cross section supportedly mounted onsaid housing and having a plurality of axially spaced spirally disposed slots therein and a plurality of apertures in the portion between the slots thereof, a blade unit comprising a shaft rotatably mounted in said housing andprovided with a plurality of oval disk-like blades mounted on the shaft in inclined relation to its axis and in spaced parallel relation to each other and in coacting relation to said cutter and shield unit, said blades having continuous peripheral shearing edges and having their major diameters inclined longitudinally of said shaft in a common plane passed through the shaft, said major diameters being of. such a length that when multipled by the cosine of the angle of inclination of the blades gives a dimension greater than the spacing between adjacent blades measured along the axis of said shaft so that'the sweep of the ends of a major diameter of one blade laterally across said cutter and shield unit overlaps the sweep of the opposite ends of adjacent blades longitudinally of said cutter and shield unit, and means for driving said blade unit shaft.

13; In a razor, a housing constituting a handpiece,a foraminate fixed cutter'and shield unit of curved cross section supportedly mounted on said housing and having a plurality of apertures therein, ablade unit comprising a shaft rotatably mounted on said housing and provided with a plurality of blades mounted on the shaft in inclined relation to its axis and in spaced parallel relation to each other and in coacting relation to said cutter and shield unit, said blades having continuous peripheral shearing edges and having their major diameters inclined longitudinally of said shaft in a common plane passed through the shaft, said major diameters being of such a length that when multipled by the cosine of the angle of inclination of the blades gives a dimension greater than the spacing between adjacent blades measured along the axis of said shaft so that the sweep of the ends of a major diameter of one blade laterally across said cutter and shield unit overlaps the sweep of the opposite ends of adjacent blades longitudinally of said cutter and shield unit, and means for driving said blade unit shaft including an electrically powered motor disposed within said housing and having driving connections to said shaft.

14. In a razor, the combination of a housing member constituting a handpiece and including a foraminate fixed cutter and shield unit of substantial length and of cylindrically curved cross section, a blade unit comprising a driven shaft rotatably mounted in said housing member in spaced parallel relation to said fixed cutter and shield unit and: relative to which said fixedcutter and shield unit is concentrically disposed, and a plurality of disc-like blades having continuous peripheral cutting edges fixedly mounted on said shaft in inclined relation to its axis and in paral lel relation to each other, said blades having continuous peripheral shearing edges and having their major diameters inclined longitudinally of said shaft in a common plane passed through the shaft, said major diameters being of such a length that when multiplied by the cosine of the angle of inclination of the blades gives a dimension greater than the spacing between adjacent blades measured along the axis of said shaft so that the sweep of the ends or" a major diameter of one blade laterally across said cutter and shield unit overlaps the sweep of the opposite ends of adjacent blades longitudinally of said cutter and shield unit and continuously contact the inside of said cutter and shield unit.

15. A razor comprising a foraminate cutter and shieldunit of substantial length and of spherically curved cross section, a blade unit comprising a driven shaft rotatably mounted in spaced parallel relation to said fixed cutter and shield unit and relative to which said fixed cutter and shield unit is concentrically disposed, and a plurality of disc-like blades fixedly mounted on said shaft and having continuous peripheral cutting edges in inclined relation to its axis and in parallel relation to each other, said blades having major and minor radii the ends of which extend to the inside of said cutter and shield unit upon rotation of said shaft, said major radii being inclined relative to the axis of said shaft at such an angle that the length of the major radii multiplied by the cosine of the angle gives a dimension that is greater than one half the spacing be'- tween adjacent blades, whereby the sweep of the ends of the major radii overlap axially of the shaft upon rotation thereof.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain June 13, 1951

Claims

6. IN A RAZOR, A HOUSING OF GENERALLY RECTANGULAR FORM HAVING FORWARDLY PROJECTING LATERALLY SPACED FLANGES, SAID HOUSING ALSO HAVING A CURVED INNER EDGE AND INWARDLY CURVED SIDE PORTIONS MERGING INTO SAID CURVED INNER EDGE PORTION PROVIDING A HANDPIECE PORTION WHICH HAS A CHAMBER THEREIN, A FORAMINATE FIXED CUTTER AND SHIELD UNIT OF CURVED CROSS SECTION EXTENDING BETWEEN SAID FLANGES, A BLADE UNIT COMPRISING A TUBULAR SHAFT ROTATABLY MOUNTED ON SAID FLANGES OF SAID HOUSING AND OPENING THERETHROUGH, A PLURALITY OF OVAL DISK-LIKE BLADES MOUNTED ON SAID SHAFT IN INCLINED RELATION TO ITS AXIS AND IN LATERALLY SPACED PARALLEL RELATION TO EACH OTHER AND IN COACTING RELATION TO SAID CUTTER AND SHIELD UNIT, SAID BLADES HAVING CONTINUOUS PERIPHERAL SHEARING EDGES AND HAVING THEIR MAJOR DIAMETERS INCLINED LONGITUDINALLY OF SAID SHAFT IN A COMMON PLANE PASSED THROUGH THE SHAFT, SAID MAJOR DIAMETERS BEING OF SUCH A LENGTH THAT WHEN MULTIPLED BY THE COSINE OF THE ANGLE OF INCLINATION OF THE BLADES GIVES A DIMENSION GREATER THAN THE SPACING BETWEEN ADJACENT BLADES MEASURED ALONG THE AXIS OF SAID SHAFT SO THAT THE SWEEP OF THE ENDS OF A MAJOR DIAMETER OF ONE BLADE LATERALLY ACROSS SAID CUTTER AND SHIELD UNIT OVERLAPS THE SWEEP OF THE OPPOSITE ENDS OF ADJACENT BLADES LONGITUDINALLY OF SAID CUTTER AND SHIELD UNIT, A MOTOR MOUNTED IN SAID HOUSING, AND DRIVING CONNECTIONS FOR SAID MOTOR TO SAID BLADE SHAFT DISPOSED WITHIN SAID HOUSING.