Abstract:
A circle cutting attachment device for a cutting torch. A torch tip sleeve is attached to the front end of the device and has a cylindrical opening passing therethrough that has a longitudinal axis that is angled forwardly through the body of the torch tip sleeve. A cradle arm adapted to engage the barrel of a cutting torch extends substantially perpendicularly above the rear end of the device. When the tip of a cutting torch is inserted into the cutting torch tip sleeve and the cradle engages the torch barrel, the torch attachment and torch are placed under bending stress which lockingly engages the tip of the torch to the torch tip sleeve and the cradle to the barrel of the torch.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an attachment device for a metal cutting torch which allows the user to accurately cut circular holes through a metal workpiece. 
     There have been a number of devices proposed over the years for aiding in cutting circular holes through a metal workpiece. One such device is described in U.S. Pat. No. 4,157,814 issued to Miller. The Miller torch attachment includes an elongated body having a torch tip support member for receiving the torch tip and which can lock the torch tip into place by a thumb screw. The gas lines connected to the other end of the torch merely rest in a U-shaped cradle. A longitudinally adjustable V-shaped scribe member is placed into a hole located at the center of the circle to be cut. In practice the Miller device is not very satisfactory because the gas lines merely rest on the cradle, thereby allowing the torch to twist out of vertical alignment which causes the torch tip to be at an angle to the workpiece resulting in the edges of the hole being cut to not be perpendicular to the planar surfaces of the workpiece. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a circle cutting attachment device for a cutting torch that is locked to the torch in a manner that eliminates any movement of the torch relative to the attachment during use. 
     The circle cutting torch attachment device includes an elongated rack having a longitudinal axis, a front end, and a rear end. The rack has a lower planar surface with a plurality of gear teeth extending therefrom. 
     A torch tip sleeve is attached to the front end of the rack. The torch tip sleeve has a body with a cylindrical opening passing therethrough. The cylindrical opening has a longitudinal axis that is at an angle to the vertical. 
     A cradle arm extends substantially perpendicularly above the rear end of the rack. A U-shaped cradle is attached to the outer end of the cradle arm. The U-shaped cradle is adapted to tightly engage the barrel of a cutting torch. 
     A centering pin carriage is located on the rack. The rack passes through a channel in the carriage. The carriage has an internally located gear wheel with a plurality of gear teeth positioned and adapted to engage the gear teeth of the rack. The carriage has means for lockingly engaging the rack. 
     A centering pin extends downwardly from the centering pin carriage, and is adapted to engage and pivot about a guide hole located in the center of a metal workpiece. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of the circle cutting torch attachment device of the present invention; 
     FIG. 2 is a side elevation view of the circle cutting torch attachment device of the present invention showing the relative positions of the attachment device and a cutting torch prior to locking the attachment device to the cutting torch; 
     FIG. 3 is a side elevation view of the circle cutting torch attachment device of the present invention showing the relative positions of the attachment device and cutting torch during the attachment process; 
     FIG. 4 is a side elevation view of the circle cutting torch attachment device of the present invention showing the relative positions of the attachment device and a cutting torch in the fully locked together mode; 
     FIG. 5 is a partial bottom plan view of the pinion gear carriage mechanism of the circle cutting torch attachment of the present invention, shown with the pinion gear guard removed; 
     FIG. 6 is a side elevation view, partially in phantom, of the pinion gear carriage mechanism of the circle cutting torch attachment device of the present invention; 
     FIG. 7 is a top plan view of the torch tip sleeve of the circle cutting torch attachment device of the present invention; 
     FIG. 8 is a side elevation view of the torch tip sleeve of the circle cutting torch attachment device of the present invention; 
     FIG. 9 is a partial, front elevation view of the torch cradle of the circle cutting torch attachment device of the present invention; and 
     FIG. 10 is a side elevation view of the shoulder bolt used to hold the pinion gear to the pinion gear carriage. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Circle cutting torch attachment  10  is shown in FIG.  1 . Attachment  10  includes an elongated horizontal rack  12  that can be made of bar stock having a substantially square cross section. The thickness of the bar stock should not be so great as to prevent rack  12  from being slightly flexible, but large enough so that rack  12  is not permanently bendable. The length of rack  12  is such as to accommodate a cutting torch, as will be discussed below. 
     The bottom planar surface of rack  12  has a plurality of gear teeth  14  extending therefrom along the entire length thereof. Rack  12  is part of a rack and pinion gear system which will become apparent from the description to follow. 
     The rear end of rack  12  is bent upwardly at substantially a right angle to the longitudinal axis of rack  12  to form vertical cradle arm  16 . A U-shaped cradle  18  is attached to the outer end of cradle arm  16 , such as by welding. 
     The front end of rack  12  is “T” shaped and fits snugly into a T-shaped slot in torch tip sleeve  20 . The T shape stabilizes sleeve  20  against movement. Torch tip sleeve  20  is attached to the front end of rack  12  by means of flat head screw  21  and dowel pin  23 . 
     Tip sleeve  20  includes a body  22  through which cylindrical opening  24  passes. The longitudinal axis “A” of cylindrical opening  24  is at an angle to the vertical as seen in FIG.  8 . By “vertical” is meant a line “V” that is perpendicular to the normally horizontal longitudinal axis extension of rack  12  (line “L” in FIG.  8 ). The angle between lines V and A is slight, being about two degrees. The direction of the angle of axis A of cylindrical opening  24  is “forwardly”, i.e., axis A angles forward from its location at top  26  to its location at bottom  28  of torch tip sleeve  20 . The purpose of angling cylindrical opening  24  forwardly will be explained below. 
     A pinion gear carriage  30  having a body  31  is located on rack  12 , best seen in FIGS. 5 and 6. Rack  12  passes through a channel  33  in body  31  of pinion gear carriage  30 . In FIG. 6 body  31  is shown in phantom for sake of clarity. 
     Centering pin  32  extends from the lower surface of body  31 . The base of centering pin  32  is positioned in an opening in the bottom of carriage  30  and held in place by screw  42 . 
     Pinion gear wheel  34  is rotatably attached to body  31  by shoulder bolt  60  which acts as an axle. Shoulder bolt  60  is shown in detail in FIG. 10, and includes head  62 , shank  64  and threaded extension  66 . 
     Pinion gear  34  has a hub including a hub extension  63  extending from one side thereof, as shown. Adjustment knob  38  is removably attached to hub extension  63  by means of screw  40 . Adjustment knob  38  rotates about head  62  of shoulder bolt  60 . Hub  63  of pinion gear  34  rotates about shank  64  of shoulder bolt  60 . Threaded extension  66  of shoulder bolt  60  is screwed into the mating threads of journal  35 . 
     The teeth of pinion gear wheel  34  mesh with teeth  14  of rack  12 . When thumb set screw  36  is loosened, pinion gear carriage  30  is free to move back and forth along rack  12  by merely pushing body  31 . Fine positioning can be made by turning adjustment knob  38 . 
     A pinion gear guard  37  covers the open bottom and open rear end of pinion gear carriage  30  (as seen in FIG. 6) and is attached to the bottom of the carriage by pan head set screws  139  engaging tapped holes  39 . 
     In operation, a cutting torch  50  is positioned so that the cutting tip  52  thereof passes through cylindrical opening  24  of torch tip sleeve  20  with shoulder  54  being in abutment with body  22 . The diameter of cylindrical opening  24  is such as to cause the walls thereof to tightly engage cutting tip  52 . Because the axis A of opening  24  is at a forward angle to vertical (as shown by line V), the rear of torch  50  and the rear of attachment  10  are inclined towards each other, i.e., the distance between the longitudinal axis of torch  50  and the longitudinal axis of rack  12  decreases as the distance away from tip sleeve  20  increases, as can best be seen in FIG.  2 . In this unstressed mode (cradle  18  being positioned beside and adjacent to barrel  56  of torch  40 ) the bottom of cradle  18  is located above the bottom of barrel  56  of torch  50 . 
     To lock torch  50  to attachment  10 , the outer end of rack  12  is pulled downwardly until the top of cradle  18  is just below the bottom of barrel  56 , as seen in FIG.  3 . Rack  12  is then pushed toward barrel  56  (the tip  42  located within torch tip sleeve  20  acting as a pivot rod) so that the longitudinal axes of rack  12  and torch  50  come into alignment. Rack  12  is then released so that cradle  18  is urged upwardly into tight engagement with the bottom of barrel  56 , as seen in FIG. 4, due to the upward bending stress imposed on rack  12  by virtue of the fact it is slightly bent and downward bending stress imposed on torch  50  by virtue of the fact is also slightly bent. 
     At the same time, the bending stresses imposed between torch  50  and attachment device  10  cause the outer surface of tip  52  of torch  50  to be urged into tight engagement with the wall of cylindrical opening  24  of torch tip sleeve  20 . Thus, attachment device  10  is tightly locked to torch  50  at both the torch tip sleeve  20  and cradle  18 . 
     The distance between the torch tip  52  and the tip “T” of centering pin  32  is adjusted by loosening thumb set screw  36  and moving pinion gear carriage  30  along rack  12 , using adjustment knob  38  for final adjustment to obtain the desired radius of the circle to be cut, and thumb set screw  36  tightened to lock in place the position of pinion gear carriage  30  on rack  12 . A hole is drilled or punched into or through the metal substrate at the center of the hole to be cut, and the tip of centering pin  32  inserted. The torch  50  is lit, and the user slowly turns the attachment  10  and attached torch  50  around the pivot formed by the tip of placement pin  32  to cut the desired circular hole through the metal substrate. 
     Upon completion of cutting the circular hole, the attachment  10  is removed from torch  50  by reversing the steps discussed above for its attachment. 
     Any cutting torch having a configuration similar to that illustrated in the drawings may be used with the hole cutting attachment  10  of the present invention. One such torch is a Victor Model CA2460 journeyman&#39;s torch. 
     Herein whenever the phrases “upper” or “lower” are used, it is with reference to the position of the components as they are illustrated in FIGS. 1-4, with “upper” being toward the top of the drawing and “lower” being toward the bottom of the drawing. Similarly, the phrases “vertical” and “horizontal” refer to the vertical or horizontal axes of FIGS. 1-4, and as described relative to lines V and L, respectively, in FIG.  8 . The “front” end of attachment  10  or torch  50  refer, respectively, to the ends containing the torch tip sleeve  20  or torch tip  52 , with the “rear” end being the end opposite the front end. 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. The scope of the present invention should, therefore, be determined only by the following claims.