US3143635A

US3143635A - Thermal wire stripper

Info

Publication number: US3143635A
Application number: US237041A
Authority: US
Inventors: James R Hooker
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-11-13
Filing date: 1962-11-13
Publication date: 1964-08-04
Anticipated expiration: 1981-08-04

Description

Aug. 4, 1964 JQ R. HOOKER 3,143,635

THERMAL .WIRE STRIPPER' Filed NOV. 13, 1962 Fig. 5

INVENTOR. /4 James R. Hoo/rer la v BYNNHTW United States Patent 3,143,635 THERMAL W STRWPER James R. Hooker, 4357 Vetter Place, La Mesa, Calif.. 'Filed Nov. 13, 1962, Ser. No. 237,041

7 Claims. (Cl. 21'9-221) This application is a continuation-in-part of abandoned application S.N. 133,273 tiled August 22, 1961, by I ames R. Hooker.

This invention relates to a device for stripping insulation from the ends of an insulated electric wire, and more particularly, to a hand-manipulated, hand-held, electrically-heated thermal wire stripper.

The removal of insulation from the ends of insulated electric connecting wires in order to prepare the wires for connection to associated apparatus has long been a troublesome chore. A number of solutions have been adopted in the art, the most acceptable one in the present state of the art being the so-called thermal wire stripper. The mechanical stripper which was popular in the prior art when connecting wires were heavier than they have presently become, can no longer be used when a high degree of reliability and ruggedness is demanded of the fabricated electronic article. The reason for this is that the trend toward lighter and more compact electronic assemblies has led to lighter and thinner electrical conductors. The smallest nick and even a shallow scratch, especially at the end of the insulation sleeve remaining on the conductor drastically increases the susceptibility of the wire to breakage. In addition, the removal of any strands from a multi-strand conductor is not permissible where the conductor is closely dimensioned to a given current capacity or other electrical or mechanical characteristic. It follows that although the mechanical wire stripper is a useful tool under certain circumstances when carefully used, there are hazards and disadvantages to its use which it is desirable to avoid. l

The present connecting wires in the electrical and electronic arts are generally insulated with a plastic material such as rubber, neoprene, nylon, teflon, etc., and these materials can be severed by melting or burning. This feature has been recognized in U.S. Patent 2,978,565 to Sullivan issued April 4, 1961, which shows a manual type thermal wire stripper. This type device hasnone of the disadvantages of the mechanical stripper, but in the .present state of theart there is lacking certain conveniences which it is the purpose of the present invention to alleviate.

Manual thermal strippers have thermal elements which perform the insulation severing process. The thermal velements must be sturdy enough so that even when heated to red heat, they will not soften and distort even after -performing the insulation removing lprocess many times. This requirement for strengthnecessitates that the thermal elements be of low electrical resistance, that is, less than an ohm with the consequence that a lowstorage, high amperage source must be utilized for heating the elements. This consideration as well as considerations of safety compel the use vof a step-down transformer so that the usual power line source can be used.

The step-down transformer for the purpose described must be capable of deliveringflS or 20 watts. In the present state of the art as shown by Patent 2,978,565, refer e'nced above, this transformerA is not an` integral part vof the manual ther-mal stripper and there is no limitation on its 'size and weight. There does not apepar to be a transformer of sufficient compactness and suitable shape in the prior art to be considered for inclusion as an integral element in a unitary handle shaped manipulated thermal wire stripper. At the same time, the use of the separate ltransformer presents a number of disadvantages. The thermal wire stripper has two stripper elements and in 3,143,635 Patented Aug. 4.,k 1964 order to avoid cross currents, arcing, etc., the step-down transformer must be provided with two separate secondary windings so that the excitation of each element is independent of the other. This requirement results in the necessity for two pairs of heavy flexible insulated electric cable to be connected to the stripper tool.

These leads are required to carry a current of ten amperes or more without appreciable heating or voltage drop. It follows that the leads must be of thick conductors and they are heavy and cumbersome and interfere with the deft manipulation of the stripper. Further, such leads are expensive, because the need for extreme flexibility requires that the leads be cable of many strands of very ine wire.

An additional disadvantage inherent in the use of the separate step-down transformer is the impracticality of remotely switching it on and off each time the stripper performs a stripping operation. The result is that the transformer is left energized continuously thereby wasting electrical energy and uselessly dissipating the life of the transformer. Still another disadvantage attendant the use of the separate transformer is that the switch must be in the heavy current secondary circuit.

It is a primary purpose of the present invention to provide an electrically energized thermal wire stripper which avoids the shortcomings of prior art devices.

It is another object of the present invention to provide a lightweight hand-size, handle-shaped thermal wire stripper which contains as an integral part, its own step-down transformer, and therefore requires for its energization only one light electrical feed cord.

Still another object of the present invention is to provide a step-down transformer of handle shape and improved eiciency to cooperate structurally and functionally as yan integral part of a hand held and manipulated thermal wire stripper.

Another object of the present invention is to provide thermal wire stripper thermal elements of improved eiiiciency to cooperate with a small eflicient step-down transformer.

Another object is to provide a thermal Wire stripper of improved ease in handling and improved economy and durability in operation.

Still another object is to provide a thermal wire stripper which is comfortably carried in one hand and in which manipulation for energization and stripping are conveniently all accomplished by the same hand.

For a better understanding of my invention together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing made a part of this specification, and in which:

FIGURE lis a perspective view of a thermal wire stripper in accordance with this invention,

FIGURE 2 is a'perspective view of the interior of the housing half cases inexploded relation,

FIGURE 3. is a vertical side view of a complete thermal wire stripper in accordance with the present invention with one half case removed, and FIGURE 3a is a modiiication thereof.

FIGURE 4 is a toppartly-in-section View of the lower thermal element and its support,

FIGURE 5 is a vertical plan View of a thermal element, and l FIGURE 6 is a schematic diagram of the step-down transformer.

Referring tothe drawing in detail, FIGURE 1 shows the stripper housing lor case -11 to comprisey two

half cases

30 and 30. Throughout this description, like parts of half case 3) and half case 30 are indicated by reference numorals and their primes respectively. yThe half cases are with few exceptions, mirror images of one another. Case frial.

case

30, 30 has an elongated

flat face

40, 40 respectively of the narrow flange.

,with pin 60'.

' o 11 is of handle shape, that is, a size and shape to be comfortably and conveniently gripped by a hand, and I have found that an elongated shape of five inches in length and transverse dimensions of one and one-half inches by one 4and one eighth inches to be suitable for manipulation by the average adult hand. The dimensions may be varied somewhat to suit smaller hands, if desirable.

In more detail, case 11 comprises a columnar portion A V34, 34' with rounded-edges and a length of about three and three eighthinches, a front

truncated pyramidalportion

35, 35 having a length of about one and one eighth inches and a rear truncated

pyramidal portion

37, 37 with a length of about one half inch. The terms front and u i rear as used herein refer to the device as grasped for Vuse with the thumb end as front. This is also the end from which the thermal stripper elements are supported.

Case 11 provides the handle for the stripper, the houslator bar 12, anchorage for a single electric supply line 76 and

insulationsupports

78 and 100 for stripper

element supporting stanchions

13, 14 and 15, 16. The stripper thermal elements V17 and 18 are electrically and ing for the transformer, the socket and support for manipumechanically affixed to the ends of

stanchons

13, 14 and u ported on

stanchions

15, 16 and can be locked in any selected position to permit accurate stripping of a selected length of insulation from a plurality of conductors.

AThe assembly of a handle, a lower fixed pair of stanchions and stripper element, and a pivoted upper pair of stanchions with its stripper element resembles and is aptly described as a jaw or mandible arrangement.

The case 11 is constructed of any strong thin material such as sheet metal or high impact strength plastic mate- Referring to FIGURE 2, it is seen that each half sol and two inwardly converging faces 42, 44, and 42', 44 s ,flange 46 extending from the front end of the case half to the rear end of flat face 40 and at right angles to flat v.face 40. A wide fiange 48 having a width equaluto` half the case thickness extends from the front end of the case to and around the rear end of the case to the front edge of the rear truncated portion Where it joins the rear end Half casef has

similar flanges

46 and 48'.l Attached to the inside surface of the narrow flange are depending

tabs

50, 52 and 5W, 52 which act as channels for the power supply line directed to and from V,the switch Vassociated with, switch button 19 at the front end of the device. The rear face of

Wide flanges

48, 48,

Vare provided with a rectangular cut-outto anchor a rubber substantially, and being affixed to flat face proximately at the rear end `near the Vwide flange thereof. A second.

element 58 of elongated cylindrical shape and having an internally Athreaded free end serves as a pivot pin for manipulator bar 12, as well as the nut for a small bolt for securing the case halves together. A ferrule 58 in case half 30 cooperates' with pivot pin 58 to support pin 58 and alsoto secure the case halves together.

A third anchor pin 60' is aixed to the front end of half case L30 along the median line thereof and at a point one-third the length of the truncated face 42 from the line ofjuncture with fiat face 40. Interiorly. of the front end of halfV case 30 is a short ferrule 60 located to cooperate Also provided lin case half 30 is a ferrule (not shown) corresponding to ferrule 56 in case half 30.

Half-case 30' is the mirror image of half case 30 with 4the exception ofthe anchor and pivot pinsas described above and two other elements. Only case half 30 is prod. former in place.

wide flange 48 a distance equal to the cross-sectiona1 height of transformer core 75. These brackets hold transformer 7 4 firmly in place in case lll.

The mechanical cooperation between the various elei land compactness. It must be capable, in spite of its small size, of energizing the thermal elements without becoming uncomfortably warm to the hand. The heat of continuous magnetization current is avoided by the provision of a switch in its primary circuit so that it is energized only when severing the insulation during a stripping operation. Even so, it is necessary that this transformer be of unique efficiency and capacity to fulfill its function in spite of its compactness. In this respect the thermal elements are also of unique shape to cooperate with the transformer by minimizing the power demand to a value compatible with the ability of the transformer.

The core 75 of transformer 74 is limited in size by the necessity for a comfortable manipulative size of the case 11. The dimensions of the case restrict the cross section of the transformer core to no greater than one and onequarter square inches. I have found that the usual transformer irons, such as A.I.S.I. types M-l4 to M-l9 are not capable of the required performance. These irons demand a prohibitively high magnetization current. In fact, with the usual transformer iron the magnetization current alone causes this smallcore to operate close to` saturation and the generation of heat in the core is excessive. I have found that a core of the diminuative size required meets the requirements capably if made of grain oriented silicon steel A.I.S.I. type M-6. This steel has a saturation level of 14,000 gausses and in the transformer Vo-f the construction shown, requires only milliamperes Aconfiguration and 0.0143 inch thick, approximately.

Each lamination has two winding windows each having a width of 0.225 inch and a height of 0.60 inch approximately. As mentioned above, the transformer primary 87 is energized by power cable '76 through a switch controlled by button 19. e

Transformer 74 is provided with two

secondary windings

88 and 88 as shown in FIGURE 6. Secondary 88 has two terminals which exit from the winding 84 on opposite sides thereof. Thus terminal 90 is connected to thermal element stanchion 16 and terminal 92 shown in FIGURE 6 but hidden in FIGURE 3 by the transformer winding is connected to stanchion 15. Terminals 90 and 92' of secondary 88 are likewise connected to

stanchions

14 and 13 respectively. The connections to stanchion's 13 and 14, are of flat flexible preferably resilient laminations to permit ready fiexure as upper jaw is operated during a stripping operation.

Referring to FIGURES l and 3, itis seen that

stanchions

15 and 16 are stationary relative to case l11. These stanchions provide both electrical connection to and mechanical support for thermal element -18. Insulation block 78 provides a rigid mechanical support for

stanchions

15 and 16. It follows that insulation block 78 itself must be rigidly affixed with respect to case 11. To Y Arms 70 and 72 are spaced apart the i length of core 75 (see FIG. 3) of transformer 74.

Flanges.y

66 and 68 are colinear with one another and spaced from the rend that block 78 will be rigidly supported and providestrong support for stanchions and 16, it is of strong `insulation material such as cloth reenforced phenolic condensate. It is roughly of truncated triangular shape in outline in its longitudinal section. Its base portion contains an arcuate relief to provide an arcuate saddle 80 for structural support with the end 82 of transformer winding 84. A rectangular relief or slot 86 is provided to enable connections to be made to the inner ends of

stanchions

15 and 16.

Block 78 by virtue of saddle 80 is mechanically coupled tightly to transformer 74 so that the length of the connections from the transformer secondary to the ther- ,mal element stanchions is a minimum and the voltage drop during use is negligible. In order to achieve these conditions, the transformer secondary terminals are located adjacent the corresponding stanchion to which connection will be made. In addition, arcuate saddle 80 engages transformer winding end 82 to prevent any relative motion between the two, with the result that block 78 is unable to work with respect to the transformer.

FIGURE 4 shows that the outer or narrow end of block 78 is provided with two parallel sockets 94 which penetrate from the front surface to slot 86. These sockets have a diameter such that threaded end portions 96 of '

cylindrical stanchions

15, 16 have a tight screw t therein. Other mechanical couplings between the block 78 and the stanchions are permissible provided the fit is suilicie'ntly secure to insure against movement of the stanchions relative to block 78 even under conditions of abuse such as dropping.- The jumper conductor 93 composed of a plurality of ribbon-like conductors of copper v.61. The saddle 80 of block 78 engages the end 82 of transformer 74 to provide resistance against pivoting of block 78 and to prevent relative motion between block 78and the transformer in order to avoid Working and fatigue of the jumper connections. In addition faces 103 and 104 of block 78 bear against

flanges

35, 35 and 48, 48 of housing 11.

Transformer 74 core 7S fits snugly between flanges 30, of the case 11 and right angle brackets 62, 64 (see FIGURES 2 and 3). The transformer thus supported, has its arcuate end 82 in proximity to establish mutual support with insulation block 78 and provide short electrical connections as aforesaid.

n The provision of a movable mandible-type thermal stripper element relative to the lixed element requires a movable insulated support for the moving element. To this end an insulation block 100 is aixed to the free end of manipulation bar 12. Manipulation bar 12 is provided with a loop portion at the posterior or back end to provide a socket 102 for engaging hinge pin 58 (FIG- URE 3). The manipulation bar 12 is lof any strong material and as shown, may be of metal channel crosssectional shape. It has a width such that it can move freely between the inner edges of

flanges

46, 46 of hous-y ing 11 when the

half cases

30, 30 are joined. The manipulation bar V12 manipulation part proper is a little longer than the transformer core. The forward end is provided with means for rigidly securing to it for motion therewith insulation block 100. Insulation block` insulation blocks are so supported as to form a fixed jaw and a movable jaw in biting relation.

Block has a pair of sockets located similarly to the sockets in block 78, for the support of stripper element stanchions 13 and 14. The sockets are so arranged that with respect to the plane of rotation of manipulation bar 12,

stanchions

13 and 15 lie inone plane parallel to the plane of rotation and 16 and 18 lie in a second plane of rotation parallel'to but spaced a selected distance away from the plane of rotation of

stanchions

13 and 15.

A leaf spring having a semi-elliptic leg 106 and a at leg 107 is provided to urge the movable stripper element away from the fixed element. Flat leg 107 rests directly upon transformer core 75 wherein proper positioning and support for spring 105 is obtained. Semielliptic leg 106 rests in the channel of manipulator bar 12.

Stripper

thermal elements

17 and 18 are shown in detail in FIGURE 5 and are required to have efficient electrical and thermal characteristics as Well as strong mechanical properties. In addition these elements must have negligible corrosion susceptibility. The desired electrical and thermal characteristics are obtained by a proper reduction in cross section of the element in the working zone and by a T-shaped relief symmetrically positioned to provide thermal isolation of the Working zone. The element is seen to have a pair of opposed similar re-entrant portions. The working zone is indicated by numeral 109. The element is provided with spaced

tab portions

112 and 113, each provided with a centrally located

aperture

114 and 115, respectively for attaching screws or the like. The tab portions are integrally connected to the working zone portion 109 by reduced

vertical legs

117 and 118, and

horizontal portions

119 and 121. A V-sllaped relief 110 and an arcuate relief 111 are provided in the working zone portion. The V-shaped relief performs two functions; it provides suflicient heat coupling with the insulated wire to be stripped to sever the insulation, and it localizes most of the heat generation in the working zone. The V-shaped or other shape such as semi-circular-shaped relief is limited in size somewhat by the smallest diameter insulated wire to be stripped in the case of directly abutting elements such as shown in FIGURE 3. It is sometimes desirable, where the depth of the relief in the Working surface is too limited by the size of the wire to be stripped to give the desired heat concentration, to provide for additional concentration of resistance in the working zone by providing additional relief such as shown by 111 in the nether surface of the elements. An increased adaptability to a wide range of wire sizes is obtained by the over-bite or overlap arrangement shown in FIGURE 3a` inasmuch as deeper V-shaped recesses can be provided to together form an adjustable diamond-shaped orifice to engage the wire to be stripped.

The concentration of resistance in the working zone results in reducing the demand for electrical energy to only that required for heating the actual working zone. In addition, rapid heating is obtained thus reducing the transfer of heat to non-working and reducing waiting and lost time in the use of the device. The foregoing described conguration of the thermal elements permits the use of a transformer of lower power capacity than would be required with the thermal elements of the prior art.

The stripper thermal elements are composed of an alloy chosen to have the characteristic above stated. The `constituent metals are cobalt 0.5 to 2.5%, chromium 20.5 to 25%, molybdenum 8 to 10%, tungsten 0.20 to 1.0%, iron 17.0 to 20%, carbon 0.05 to 0.15%, silicon not exceeding 1.0%, manganese not exceeding 1.0%, and the balance nickel. This material has excellent oxidation resistance to 2200 degrees F.

The transformer windings for the dimensional embodiment given supra are as follows: Primary winding- 440 turns of No. 28, secondary windings-each 4 turns of No. 14.

D An operating example of a stripper element has the following dimensions:

' Inches Total height 0.312 Thickness 0.032 Total width 0.563 Width and height of

tabs

112 and 113 0.186

Length portions

117 and 118 0.054 Width of

side legs

117 and 118 0.062

Radius Vof relief 111 and length of arc 0.500 and 0.2

Manipulator bar 12 is limited in the extent of opening by member 112. This member is anchored in any convenient manner in fixed jaw '7S and is accommodated by lslot 101 in jaw 100. Member 112 is provided at its free Vtactor 95 against the tension of spring 97 into contact with contacts 108l to bridge them. One of contacts 10S is connected to one of conductors 76 and the other of contacts 108 connects to one terminal of transformer primary 87. The other conductor of supply line 76 connects directly to the other terminal of transformer primary S7. In operation, the manipulator bar 12 is compressed to cause the thermal elements to press against the insulation to be severed, switch 19 is pressed inward to energize the transformer and heat the thermal elements. When the insulation is severed, switch button 19 is released while bar 12 remains squeezed down to pull the severed insulation off of the conductor being prepared. It is, therefore, seen that the transformer need be energized only for the severing operation and that this is a very brief period, resulting in maximum efficient use of electrical energy and a minimum demand on the transformer. An additional advantage of this system is that the stripping elements are not continuously heated during the stripping operation with the result that the cool elements cleaner strip the severed insulation sleeve off the wire and avoid the generation of excess molten debris. Furthermore, the fumes generated by heating some plastic materials to a melting or higher temperature are irritating and even to some extent, toxic, and the present device keeps the generation of such fumes to an absolute minimum.

This invention has been described with reference to a preferred embodiment, but it is apparent that there may be numerous equivalents of the specific details given which may be in accordance with the spirit of this invention;

accordingly, it is desired that it be understood that this invention is to be considered limited only by the appended claims taken in the light of the prior art,

What is claimed is:

1. A manually held thermal wire stripper comprising in combination a fixed jaw and a movable jaw each having a thermal stripper member on the working end thereof, a hollow elongated case of channel cross sectional shape and hand gripping size and having a uniform cross section middle portion and truncated front and rear ends, an electrical transformer supported in said case middle portion and having primary and first and second secondary windings, said fixed jaw comprising a dielectric block having a front portion and a rear portion, said front portion having an intermediate part inwardly inclined and an end part at right angles with respect to the fore and aft direction thereof, a pair of co-extensive parallel elongated conductive stanchions spacedly supported at one end in the front right angle part of said dielectric block, means fxedly supporting said dielectric block in the front truncated portion of said case with the fore and aft direction of the block aligned with the direction of elongation of the case vand with the rear end of the dielectric block abutting the adjacent end of the transformer; a resistance plate member electrically connected to and affixed in bridging transverse relation to the `working end of the stanchions; said movable jaw comprising an elongated movable manipulator bar, a pair of moving conductive stanchions and a movable resistance plate member, said manipulator bar having a middle portion and front and rear end portions and having an overall length equal approximately to the length of the transformer plus-the length of the fixed jaw dielectric block in-the direction of elongation of the case, means pivotably supporting the rear end of the manipulator bar in the rear end p0rtion of the case with an elongated portion of said manipulator bar positionedwithin the open side of the case in close proximity to the adjacent case walls and extending outwardly of said case along the length thereof, said ,manipulator bar front end portion having an intermediate part inwardly inclined with respect to the manipulator bar middle portion, and an end part at a right angle to the manipulator bar middle portion, means anchoring one end of each of said movable stanchions in the end part of the manipulator bar front end portion, means supported on said transformer for resiliently biassing said manipulator bar away from the transformer in said case, and limit stop-means limiting the outward travel of the manipulator bar, means electrically connecting and mechanically affixing said movable resistance plate member to the working end of the movable stanchion; an Velectrical pushV button switch, means iixedly supporting said switch on the inner surface of the manipulator bar front end portion inwardly inclined part with the push button thereof extending through and outwardly of the manipulator bar; said transformer primary winding being connected in electrical series with said switch and a power connect'mg cable, means electrically connecting the terminal ends of one of the secondary windings to the fixed ends of the fixed jaw stanchions, and exible electrical connecting means connecting the terminal ends of the other secondary winding to the manipulator bar end of the said movable stanchions, whereby the thermal wire stripper is adapted to be powered directly from standard alternating current sources, and said manipulator bar is adapted to be manually urged inwardly by the palm of the hand to engage said resistance plates with insulation to be severed and said push button is adapted to be operated by the thumb of the same hand to energize said transformer to heat the resistance plate members only so long as is necessary to complete a stripping process.

2. The device of claim 1 in which each resistance plate member has a working portion and a working edge, and is a rigid metal plate of generally rectangular external configuration, said resistance plate member having a T-shaped section symmetrically removed therefrom and completely severing the plate portion opposite the working portion to provide a pair of separated mounting tabs, the working portion of the plate member having a wire insulation receiving notch in the central portion thereof, and being further progressively reduced in cross section toward the center thereof by an arcuate relief convex toward the working edge thereof, whereby the electric power demand for adequate heating of the resistance plate member is minimized by the concentrated utilization of energy in a confined working zone area to thereby permit the effective utilization of the contained transformer and whereby the strength and rigidity of the r-,esistance .plate is at the same time maximized.

3. A hand-held thermal wire stripper comprising in combination,

(a) an upper andV a lower electrically conductive jaw member each having an anchored end anda working end,

(b) an elongated housing of channel cross sectionalV shape having a front portion, a middle portion and a rear portion, said front portion being truncated and hand grip wall members extending adjacent to and partially enclosing said jaw members,

(c) a resistance plate member having a working zone for severing insulation and having concentrated electrical resistance in the working zone, attached to the working end of each jaw member,

(d) first insulation block means having a length substantially equal to the length of the housing truncated front portion, means iixedly attaching the anchored end of the lower jaw member to said in sulation block means, means ixedly supporting said insulation block means in the housing truncated front portion,

(e) an elongated manipulator bar of dielectric material, means pivotably supporting one end of the manipulator bar in said housing open side proximate the rear end thereof, said manipulator bar having a hand manipulating portion equal substantially to the length of the housing middle portion and having a lower elongated portion thereof confined within the adjacent walls of the housing to prevent lateral movement thereof and an upper elongated portion extending outwardly of said housing along the length thereof and a front portion adjacent the case front truncated portion extending inwardly; means fixedly attaching the anchored end of the upper jaw member to said manipulator bar inwardly extending portion whereby said upper jaw member is movably supported for motion in a xed plane toward and away from the xed lower jaw,

(f) an elongated electrical transformer supported in the housing in the uniform cross section portion, said transformer having a magnetic core, a primary winding adapted to be connected to a power source, and two secondary windings, means electrically connecting one of said secondary windings in series with the lower jaw resistance plate member,v and means for flexibly electrically connecting the other of said secondary windings to the movable jaw resistance plate member,

(g) resilient biassing means supported on said transformer magnetic core to support said transformer against movement in said housing and to urge said manipulator bar outwardly along the housing.

4. The device of claim 3 in which said transformer secondary windings have terminals at the same end of the transformer, said transformer being supported in the housing with said terminals proximate the anchored ends of said jaws and the electrically connecting means connecting the terminals of the secondary windings to the respective jaw members are heavy iiexible electrical conductors of minimal length.

5. The device of claim 4, wherein the rst insulation block means has a front end extending out of the truncated front portion of the housing and a rear end iixedly supported in the truncated portion of said housing against said transformer core, a slot in said insulation block means transverse to the direction of elongation of the housing, a pair of spaced sockets extending from the front end of the insulation block means to the slot and lying in a plane transverse to the direction of manipulation of the upper jaw, said lower electrically conductive jaw member comprising a pair of rigid metal rods anchored at one end in said sockets, means electrically and mechanically attaching said heavy flexible electrical conductors to the metal rods in said transverse slot, said insulation block means being provided with an aperture transverse with respect to said sockets in the portion rearward of said slot, securing means passing transversely through the lateral walls of said housing and said insulation block aperture to fixedly secure said lower jaw and said transformer in and to said housing.

6. The device of claim 5 wherein the manipulator bar front inwardly inclined portion is provided with a switch button receiving aperture passing transversely therethrough, a push button electrical switch, means iixedly attaching said switch to the inside surface of the manipulator bar inwardly inclined portion with the switch push button extending outwardly of said manipulator bar through said aperture, electrical connecting means electrically connecting said switch in electrical series connection with the transformer primary winding and power supply connecting means, whereby said thermal wire stripper jaws are manipulated by the palm of the hand and the thermal resistance plate members are electrically heated at will by thumb manipulation of the switch button.

7. An insulation stripper element for a thermal wire stripper comprising a metallic resistance plate member of generally rectangular shape having a working edge, a generally T-shaped slot symmetrically located in said resistance plate member with the end of the stem of the T extending through the edge of the resistance plate member opposite the working edge thereby providing adjacent isolated terminal tab members in said resistance plate member, said resistance plate member working edge being provided with a wire receiving notch in the middle thereof, the cross of the T-slot extending parallel to the working edge of the resistance plate member, and the portion of the resistance plate member adjacent the upper edge of the cross of the T-slot having a centrally located arcuate relief, convex toward the working edge to concentrate the resistance of the resistance plate member in the middle portion of the working edge to thereby concentrate the generation of electrical heating in the middle portion while preserving the rigidity and strength of the resistance plate member to prevent distortion thereof as a result of stripping operations.

References Cited in the file of this patent UNITED STATES PATENTS 1,595,799 Massingham Aug. 10, 1926 2,192,056 Watts Feb. 27, 1940 2,709,743 Mitchell May 31, 1955 2,745,939 Lenk May 15, 1956 2,768,276 Arntzen Oct. 23, 1956 2,978,565 Sullivan et al. Apr. 4, 1961 UNITED".vk STATES PATENT OFFICE CERTIFICATE OF CORRECTION; Patent No. 3,143,635 August 4, 1964 g James Ra Hooker It is hereby certifiedl that error appears in the above numbered patient4 requiring correction and that the said Letters Patent should read as corrected below.,

Column I, line 56, for' nstorage" read voltage line 66, for "apepar". read appear Signed and sealed this 5th day of January 1965.

Att-esta; ERNEST We. SWIDER' EDWARD J. BRENNER` Attesting Officer Commissionerof Patents UNITED STATES PATENT GEEICE CERTIFICATE 0F CORRECTION August 4, 1964 Patent No. 3,143,635

James Ro Hooker in the above numbered pat#- that error appears ters Patent should read as It is hereby certified t the said Let ent. requiring correction and the,

Column l, line 56, for "storage" re line 66xl for "apepar" read appear Signed and sealed this 5th day of January 1965.

(SE-ALJ Attest:

EDWARD J BRENNER.

ERNEST W. SWIDER Attesting Officer Commissioner. of Patents

Claims

3. A HAND-HELD THERMAL WIRE STRIPPER COMPRISING IN COMBINATION, (A) AN UPPER AND A LOWER ELECTRICALLY CONDUCTIVE JAW MEMBER EACH HAVING AN ANCHORED END AND A WORKING END, (B) AN ELONGATED HOUSING OF CHANNEL CROSS SECTIONAL SHAPE HAVING A FRONT PORTION, A MIDDLE PORTION AND A REAR PORTION, SAID FRONT PORTION BEING TRUNCATED AND HAND GRIP WALL MEMBERS EXTENDING ADJACENT TO AND PARTIALLY ENCLOSING SAID JAW MEMBERS, (C) A RESISTANCE PLATE MEMBER HAVING A WORKING ZONE FOR SEVERING INSULATION AND HAVING CONCENTRATED ELECTRICAL RESISTANCE IN THE WORKING ZONE, ATTACHED TO THE WORKING END OF EACH JAW MEMBER, (D) FIRST INSULATION BLOCK MEANS HAVING A LENGTH SUBSTANTIALLY EQUAL TO THE LENGTH OF THE HOUSING TRUNCATED FRONT PORTION, MEANS FIXEDLY ATTACHING THE ANCHORED END OF THE LOWER JAW MEMBER TO SAID INSULATION BLOCK MEANS, MEANS FIXEDLY SUPPORTING SAID INSULATION BLOCK MEANS IN THE HOUSING TRUNCATED FRONT PORTION, (E) AN ELONGATED MANIPULATOR BAR OF DIELECTRIC MATERIAL, MEANS PIVOTABLY SUPPORTING ONE END OF THE MANIPULATOR BAR IN SAID HOUSING OPEN SIDE PROXIMATE THE REAR END THEREOF, SAID MANIPULATOR BAR HAVING A HAND MANIPULATING PORTION EQUAL SUBSTANTIALLY TO THE LENGTH OF THE HOUSING MIDDLE PORTION AND HAVING A LOWER ELONGATED PORTION THEREOF CONFINED WITHIN THE ADJACENT WALLS OF THE HOUSING TO PREVENT LATERAL MOVEMENT THEREOF AND AN UPPER ELONGATED PORTION EXTENDING OUTWARDLY OF SAID HOUSING ALONG THE LENGTH THEREOF AND A FRONT PORTION ADJACENT THE CASE FRONT RUNCATED PORTION EXTENDING INWARDLY; MEANS FIXEDLY ATTACHING THE ANCHORED END OF THE UPPER JAW MEMBER TO SAID MANIPULATOR BAR INWARDLY EXTENDING PORTION WHEREBY SAID UPPER JAW MEMBER IS MOVABLY SUPPORTED FOR MOTION IN A FIXED PLANE TOWARD AND AWAY FROM THE FIXED LOWER JAW, (F) AN ELONGATED ELECTRICAL TRANSFORMER SUPPORTED IN THE HOUSING IN THE UNIFORM CROSS SECTION PORTION, SAID TRANSFORMER HAVING A MAGNETIC CORE, A PRIMARY WINDING ADAPTED TO BE CONNECTED TO A POWER SOURCE, AND TWO SECONDARY WINDINGS, MEANS ELECTRICALLY CONNECTING ONE OF SAID SECONDARY WINDINGS IN SERIES WITH THE LOWER JAW RESISTANCE PLATE MEMBER, AND MEANS FOR FLEXIBLY ELECTRICALLY CONNECTING THE OTHER OF SAID SECONDARY WINDINGS TO THE MOVABLE JAW RESISTANCE PLATE MEMBER, (G) RESILIENT BIASSING MEANS SUPPORTED ON SAID TRANSFORMER MAGNETIC CORE TO SUPPORT SAID TRANSFORMER AGAINST MOVEMENT IN SAID HOUSING AND TO URGE SAID MANIPULATOR BAR OUTWARDLY ALONG THE HOUSING.