Title:
UNIBIT WITH REPLACEMENT BLADE
Kind Code:
A1


Abstract:
A unibit with replacement blade provides economical refreshing of the many cutting facets of a unibit drill bit with a unibit replacement blade that is releasably secured in the unibit body. In one aspect of the invention, a replacement blade with cutting edges on one or both opposite side edges is releasably locked into the unibit body by a transverse locking screw. The blade can be provided with an integral tip drill when desired. In another aspect of the invention, one or more replacement blades is releasably secured in a recess in the unibit body with a simple blade lock mechanism, the blades being positioned symmetrically around the axis of the drill. In one embodiment, the blade lock is an eccentric cam member that rotates into and out of locking engagement with the blade. Other blade locks include clamping screws, screws through the blade, cam plates, tapered blades, and blade receiving grooves. Another aspect of the invention provides a replaceable tip drill.



Inventors:
Seeley, Scott C. (Grand Rapids, MI, US)
Application Number:
11/842424
Publication Date:
02/07/2008
Filing Date:
08/21/2007
Primary Class:
International Classes:
E21B10/00
View Patent Images:



Primary Examiner:
HOWELL, DANIEL W
Attorney, Agent or Firm:
Oppenhuizen Law PLC (Grand Rapids, MI, US)
Claims:
What is claimed is:

1. A unibit with replacement blade comprising: a body of rotation having an axis, the body including a generally conical head having a base and a tip at opposite axial ends thereof and having an inclined outer surface extending between the base and the tip, the head further including a mounting shaft extending axially from the base for mounting the unibit in a rotating tool; the head including an axially extending recess in at least one side thereof, the recess being formed in the outer surface of the head and extending inwardly toward an interior of the head; a replacement blade that fits in the recess, the blade having a stepped cutting surface on at least one outer side that extends outwardly beyond the outer surface of the conical head, such that the cutting surface of the blade engages edges of a hole in a work piece before the work piece engages the head; and a blade lock that releasably holds the blade in a secure cutting position in the recess in the head.

2. A unibit as in claim 1 wherein: the recess comprises an axial slot extending laterally all the way through the conical body such that the sides of the slot are open at opposite sides of the inclined outer surface of the head; the blade fits in the slot and includes stepped cutting surfaces on at least one of two opposite sides edges of the blade, the sides with stepped cutting surfaces protruding beyond the inclined surfaces of the body at the sides of the body; and the blade lock comprises a fastener that engages the blade and locks it in position in the body.

3. A unibit as in claim 2 wherein: the blade lock fastener comprises at least one locking screw that engages a threaded opening formed in the body transversely to the slot and extending from the inclined outer surface into the slot, the locking screw engaging and locking the blade in the slot when the screw is threaded into the opening, the blade being releasable by axially withdrawing the screw from the slot.

4. A unibit as in claim 2 wherein the blade includes stepped cutting surfaces on both of the opposite side edges of the blade and both side edges extend outwardly beyond the inclined surfaces on both opposite sides of the body.

5. A unibit as in claim 2 wherein cutting surfaces on the blade extend all the way to a tip end of the blade, the cutting surfaces at the tip serving as a tip drill to initiate a hole in material to be drilled.

6. A unibit as in claim 2 wherein the blade has a generally flat tip end without tip drill cutting edges for initiating a hole in previously undrilled material.

7. A unibit as in claim 1 wherein the blade lock comprises at least one fastener that extends through an opening in the body that extends transversely across the slot, the blade having a mating opening through which the fastener fits when the blade is in a mounting position in the slot.

8. A unibit as in claim 7 wherein the blade lock includes at least two spaced fasteners that extend through spaced openings in the body and blade.

9. A unibit as in claim 1 wherein the blade lock comprises a threaded fastener that extends first through an opening in the body on one side of the slot then through a mating opening in the blade, and then engages a threaded opening in the conical body on the opposite side of the slot.

10. A unibit as in claim 9 wherein the fastener has a head that includes a conical surface on an underside thereof, the conical surface engaging the opening in the blade and serving to center the opening in the blade with respect to the fastener.

11. A unibit as in claim 2 and further comprising stability means for enhancing the stability of the blade and proper positioning of the blade in the body, the stability means comprising a mating projection and slot in the edge of the blade and interior of the handle recess that properly positions the blade in the recess.

12. A unibit with replacement blade, comprising: a body of rotation having an axis, the body of rotation having first and second opposing ends, the body having a shaft extending along the axis toward a second end from the first end, the body having a head extending toward the first end from the second end, the head comprising two blade support members separated by an axial slot, with the head having a tip at the second end and a base at an opposite end of the head; and a replacement blade releasably secured in the slot, the blade having two inclined sides, with cutting edges on at least one of the sides, the cutting edges including a series of steps and ramps of increasing diameter, the blade being secured in the slot so the cutting edges extend beyond the body in a direction that is radially outward from the axis.

13. The unibit of claim 12 wherein the replacement blade further includes a tip drill with a cutting tip at one end opposite the base.

14. The unibit of claim 12 wherein the replacement blade is releasably secured between the blade support members with one or more screws mounted transversely in the body for engagement with the blade.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of co-pending U.S. patent application Ser. No. 11/430,458, entitled Unibit With Replacement Blade and filed on May 9, 2006, by Scott C. Seeley, now co-pending, the disclosure of which is incorporated here by reference.

BACKGROUND OF THE INVENTION

The invention relates generally to hole drilling bits that are used to drill holes in sheet metal and other sheet materials. More specifically, the invention relates to a stepped multiple hole size drill bit, which is commonly known as a unibit or step drill. Unibits are relatively more expensive than single size twist drills and tend to be used frequently because of their versatility of being capable of drilling a variety of hole sizes. This frequent use also causes them to have a relatively short life. Further, unibits are typically not re-sharpened when worn because of the level of effort and expense to sharpen their many cutting facets.

One object of the present invention is to provide a unibit that can economically be resharpened by means of one or more easily replaceable blades.

BRIEF SUMMARY OF THE INVENTION

Accordingly, a unibit with a replacement blade of the invention provides economical refreshing of the many cutting facets of a unibit with a unibit body and replacement blade that is releasably secured to the unibit body by a blade lock without a complicated mechanism. In one preferred embodiment of the invention, a single replacement blade having cutting edges on one or both opposite side edges is secured in a slot in a conical head of a body then are threaded by screws that extend through the body on one side of the slot, then through an opening in the replacement blade, and into the second side of the body the blade can be provided with or without an integral tip drill. The conical head can have straight or stepped sides. In another embodiment of the invention, one or more replacement blades having cutting edges on one side are locked in blade retaining recesses formed in the conical head of the unibit body. The blade lock can be an eccentric cam member that rotates into and out of locking engagement with the blade. In other embodiments of the invention, other types of novel blade locks are employed to lock the replacement blade in place. Another aspect of the invention provides a replaceable tip drill and a fastener that urges the tip drill into a seated position in the unibit body. The unibit of the invention may be provided with one or more replaceable blades.

These and other features or benefits of the invention will be recognized from this specification, including the claims and the drawing figures, by one having ordinary skill in the art and by those who practice the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an exploded side elevation view of a first alternative embodiment of a unibit with replacement blade of the invention;

FIG. 2 is a top plan view of a replacement blade thereof, along line II-II of FIG. 1;

FIG. 3 is a bottom plan view thereof,

FIG. 4 is a top plan view of a body of the unibit with replacement blade of FIG. 1;

FIG. 5 is an end view of the embodiment of FIG. 1;

FIG. 6 is an end view of a second alternative embodiment thereof,

FIG. 7 is an end view of a third alternative embodiment thereof,

FIG. 8 is an end view of a fourth alternative embodiment thereof,

FIG. 9 is an end view of a fifth alternative embodiment thereof,

FIG. 10 is a perspective view of a sixth alternative embodiment of a unibit with replacement blade of the invention;

FIG. 11 is a plan view thereof;

FIG. 12 is a side elevation view thereof,

FIG. 13 is an end view thereof, taken from the tip end thereof,

FIG. 14 is a side elevation view of a seventh alternative embodiment of a unibit with replacement blade of the invention;

FIG. 14a is an enlarged fragmentary view of an edge thereof, showing an undercut at a junction between successive steps of a body thereof,

FIG. 15 is a plan view of the embodiment of FIG. 14;

FIG. 16 is a side elevation view of a clamping screw thereof,

FIG. 17 is ahead end view thereof;

FIG. 18 is a tip end perspective view of a replacement blade of the embodiment of FIG. 14;

FIG. 19 is a side elevation view thereof,

FIG. 20 is an edge view thereof,

FIG. 21 is a cross section view thereof, taken along line XXI-XXI of FIG. 19;

FIG. 22 is a side elevation view of the tip drill of the embodiment of FIG. 14;

FIG. 23 is a plan view of the tip drill of FIG. 22;

FIG. 24 is an end view of the tip drill of FIG. 22;

FIG. 25 is a perspective view of one preferred embodiment of a unibit with replacement blade of the invention;

FIG. 26 is an exploded perspective view of the embodiment of FIG. 25;

FIG. 27 is a plan view of the unibit of FIG. 25;

FIG. 28 is an end view of the embodiment of FIG. 25, taken from the tip or left end as shown in FIG. 27;

FIG. 29 is an end view of the embodiment of FIG. 25, taken from the shaft or right end as shown in FIG. 27;

FIG. 30 is a cross-sectional view of the embodiment of FIG. 25 taken along line XXX-XXX of FIG. 27;

FIG. 31 is perspective view of the replacement blade of FIG. 25;

FIG. 32 is a plan view of the replacement blade of FIG. 31;

FIG. 33 is an edge view of the replacement blade of FIG. 31;

FIG. 34 is a cross-sectional view of the replacement blade of FIG. 31, taken along line XXXIV-XXXIV of FIG. 32; and

FIG. 35 is an end view of the replacement blade of FIG. 31, taken from the tip or left end as shown in FIG. 31.

DETAILED DESCRIPTION OF THE INVENTION

With general reference to the drawing figures, a first embodiment of a unibit with a replacement blade according to the invention 20 has at least a body 22, a replacement blade 24 (sometimes referred to as a replaceable blade), and a blade lock 26. The body is a body of rotation about an axis “A” and has two opposing ends 27 and 29 (FIG. 4). A shaft portion 28 extends from one end 29 (first end) toward the opposing end 27 (second end) and a generally conical head 30 extends from the opposing end 27 toward the shaft. The head 30 includes a tip 31 at end 27 and a base 33 that joins the shaft 28. The base can have an enlarged rim 35 that restrains the head from passing entirely through a drilled hole in sheet material. The enlarged rim is optional and may not be employed in all cases. In the first embodiment, the head 30 has an inclined outer surface 37 that includes a series of steps 32 of progressively increasing diameter and a series of ramps 34 interposed between and connecting adjacent steps. While the steps and ramps in the head do not have cutting edges, they improve the fit and orientation of the unibit in the drilled hold in the panel or sheet material being drilled and improve the drilling action.

The shaft 28 is adapted to be secured into a rotating machine, such as a drill or the like (not shown). For example, the unibit 20 may be used with one-quarter inch, one half inch or other sizes of drills and the like. Thus, the shaft may be sized accordingly and in consideration of torque loading on the head 30, as is understood by one having ordinary skill in the art. The body 22 may be made of any appropriate cutting tool holding or foundation material, such as 4140 or 6150 steel, with 4140 steel being less hard and generally less expensive. Other types of steel or alloys will work. Unlike conventionally known unibits, which have a cutting edge integral with their body, the cutting edge of the unibit according to the invention is incorporated in a separate replacement blade. Thus, the body does not need to be formed of the same hardened cutting tool material as the blades and their cutting edges. This can reduce the cost of the tool significantly.

In the first embodiment, a blade receiving recess 40 is formed in each side of the head 30 and releasably receives a corresponding replacement blade 24. As shown in the drawings, the blade receiving recess is a generally V-shaped sectional void in the head 30 that resembles a quarter-section-like portion from the head. This is not a true quarter-section, however, in that the sides or walls 42 and 48 of the section are not aligned (coplanar) with the axis of rotation “A.” Rather, as shown in the end view of the FIG. 5, the plane of side 48 is overextended beyond the axis. The extent of overextension is preferably about the thickness of the replacement blade 24, such that a cutting edge 46 of the replacement blade at a face surface 54 of the blade lies in a plane that extends generally through the axis “A.”

The replacement blade 24 is a generally triangular shaped plate member that is constructed of a suitably hard material, such as 6264 tool steel, for example. In the first embodiment, the blade has two long legs 44 and 45 and a short leg 47. One of the long legs 44 forms an inclined outer edge of the blade. This leg has a stepped cutting edge 46 that is defined by a series of flats 50 and ramps 52. In use, the head and blade will be rotated and the blade cutting edge will be along a leading face or surface 54 of the blade, relative to the direction of rotation.

The flats 50 are generally parallel with the reference axis “A” when the blade 24 is installed in the head 30, and are spaced a progressively increasing distance from the axis. Again, as with the stepped configuration of the head, the ramps 52 of the replacement blade extend between adjacent flats. The flats 50 and ramps 52 of the blade correspond to the steps 32 and ramps 34 of the head but extend slightly radially outward from the head 30. Thus, the cutting edge is exposed to do its job of cutting, while the head is a foundation for the blade and holds and positions the blade.

The blade lock 26 releasably secures the blade 24 in the receiving recess 40 and is configured in the first embodiment of the invention as an eccentric cam 59 rotatably mounted in the blade receiving recess 40 of the head 30. The blade lock 26 has an eccentric cam head 60 on a pivot shaft 62. The shaft extends into a corresponding hole in the head. Preferably, the shaft and the hole are provided with cooperating screw threads that engage in forced fit. Thus, disengagement or removal of the blade lock from the head in use is resisted by the force fit engagement of the shaft with the head and their screw threading.

Another feature of the first embodiment of the invention is that an inner end 63 of the blade receiving recess 40 in the head 30 of the unibit is curved outwardly. This curved end directs metal shavings radially outwardly from the tool and prevents shavings from collecting in the recess.

In a second embodiment of the invention, shown in FIG. 6, rather than locking the blade in place with the eccentric cam 60 of FIG. 1, the blade can be locked in place by a blade lock 26′ that includes a cam plate in the form of angle plate 71 that bears against the outside of the blade. A bolt 73 extends through a slot 72 in the angle plate and screws into a threaded, inclined opening 75 in the body of the unibit. Tightening the bolt urges the bolt against an inclined outer surface of the angle plate and causes the angle plate to clamp the blade in position.

In a third embodiment of the invention, shown in FIG. 7, blade lock 26″ includes a screw or bolt 77 that extends into a threaded opening 79 that is parallel with the side of the blade. A cam plate 81 with an inclined side is positioned between the blade and a screw head 83, so that the head of the screw urges the plate against the blade as the screw is screwed into the opening.

As an alternative to the use of a cam plate, the replacement blade itself 85 can be formed with an inclined side 87, as shown in blade lock 26′″ in FIG. 8. In this fourth embodiment, axial movement of screw 89 into hole 90 causes the head 91 of the screw to engage the inclined surface and urge the blade into a locked position. The head of the screw can be tapered to mate with the incline of the sides of the blade.

In a fifth embodiment of the invention, shown for exemplary purposes in FIG. 9, the blade receiving recess 40′ of the body of the unibit can be provided with an elongated groove 93 that extends axially in wall 42 adjacent wall 48. The groove receives an inner edge 45 of the blade and holds it in place while any of the blade locks clamp the blade in position. The groove 93 for the blade lock is shown for illustrative purposes in connection with the embodiment of FIG. 9. This groove also can be used, however, for other embodiments.

Another feature of the previous embodiments of the invention is a replaceable tip drill 64 that is releasably mounted in the tip of the unibit. The tip drill 64 may be provided either in combination with a unibit having a replacement blade feature, or in a unibit having a fixed, non-replacement blade. Tip drill 64 includes a shaft 66 that is securely and releasably received in a cooperating shaft receptacle 68 in the tip 31 of the unibit head 30. A set screw 70 or the like may be used to secure the tip drill to the unibit head. Other means for non-rotatably securing the tip drill in the head can be employed, including a mating non-circular (e.g., square) shaft and receptacle. The tip drill is formed of a cutting tool material, such as 6240 steel. The tip drill has a sharpened drill point 80 for starting a drill hole. Desirably, the tip drill also has at least one drill step comprising a ramp 82 and a flat 84 at an increased diameter that mates with the smallest diameter flats and ramps at the top of the body. It should be noted that a tip drill is not necessarily employed in every case. In some instances, such as when the bit is employed in sheet material having a pre-formed hole, the bit might not employ a tip drill at all.

The unibit 20 has at least one replacement blade according to the inventive concept. As shown in FIG. 1, a second replacement blade preferably is provided in the first embodiment in a generally diametrically opposed and rotationally balanced position. One having ordinary skill in the art may identify uses and situations where more than two blades is desired, in which case the blades are disposed symmetrically around the head.

A sixth embodiment of the present invention is shown in FIGS. 10-13. In this embodiment, as in the previous embodiment, unibit 100 includes a body 102, a replacement blade 104, and a blade lock. The blade lock includes a screw 106 positioned adjacent to the replacement blade 104 that extends parallel to or preferably at a slight inward angle toward the replacement blade. The blade lock also includes a screw 108 that extends through an opening 110 in the heel 128 of the blade. The unibit 100 (also called a step drill) can include an enlarged rim 112 at the base 113 of the conical head 111 to prevent the drill from passing all the way through an opening in sheet material. The enlarged rim is optional and may not be employed in all circumstances. A mounting shaft 114 extends axially from the base 113 of the head 111. Shaft 114 has flattened portions 116 spaced around the shaft to prevent the shaft from rotating in the driver. The drill includes a replaceable drill tip 118 having a stepped conical head 120 mounted on a shaft 122 that extends into an opening in the end of the drill. Shaft 122 has a flattened surface that faces set screw 124, which is threaded in opening 126 adjacent the end of the drill. Set screw 124 holds the tip drill in place.

The primary difference between the drill in FIGS. 10-13 and the drill of FIG. 1 is the manner in which the replacement blade is mounted to the head of the drill. Screw 106 is similar to screw 60 in FIG. 1, except that it does not require an eccentric outer surface as in FIG. 1. Preferably, screw 106 is at a slight angle with respect to the surface of the blade, and the head of the screw has a slightly tapered surface (similar to FIGS. 7-9).

The screw thus tightens against the sides of the blade as it is advanced inwardly into the tapered screw hole. Another distinctive feature of the embodiment of FIGS. 10-13 is that screw 108 firmly retains the heel 128 of the blade in place. Screw 108 has a head with a tapered outer surface that mates with a tapered surface in opening 110 so that screw 108 can be countersunk into the opening and still clamp the heel of the blade to the body of the unibit. A screw having a head larger than the opening through which the screw fits also would serve the same clamping purpose, although a protruding screw head could have the disadvantage of impairing somewhat the discharge of shavings from the drill bit. The use of the additional clamping screw 108 more securely attaches the replacement blade in place in the body of the unibit.

In order to provide an even more secure attachment of the replacement blade to the body of the unibit, the recess in which the blade of FIG. 10 is mounted can have a groove 130 formed therein in which the adjacent edge of the unibit fits, in the manner of groove 93 in FIG. 9.

The blade formed in the foregoing manner provides a more secure attachment for the replacement blade than that described in the first six embodiments. This embodiment may therefore be preferred for at least some applications where one of the first six embodiments is used.

A seventh embodiment 200 of the present invention is shown in FIGS. 14-24. Unibit 200 includes a body 202 and a replacement blade 204. The body includes a shaft 208 at one end 209 and a conical head 210 at a second end 207 of the body, all as in the prior embodiments. The outer surface of head 210 includes a plurality of steps 212 progressively increasing in diameter and a series of ramps 214 interposed between the adjacent steps.

Shaft 208 includes flattened portions 216 spaced around the periphery of the shaft for non-rotatably mounting the shaft in a driver chuck.

The head 210 of the body is similar to the previous embodiment except that a small undercut portion 217 is formed between the adjacent steps and ramps of each step in the drill, as shown in FIG. 14a. In a typical drill having a maximum outer diameter of about 1 inch, the undercut may be approximately 0.008 inches deep.

Replacement blade 204 is constructed in a manner similar to replacement blade 104 of FIGS. 10-13, except that the heel 220 of the blade includes a slot 222 instead of a hole. A screw 224 extends through the slot into a threaded opening in the head of the drill body. The slot makes it possible to adjust blade position or replace a blade simply by loosening the screw and sliding the blade out of the slot instead of having to remove the screw 224 completely from the body.

Another feature of replacement blade 204 is that the blade includes a groove 226 adjacent and parallel to the leading edge of the blade. This groove improves the operation of the blade.

The replacement blade 204 is held in position by means of clamping screw 228, shown in FIGS. 16 and 17. In an exemplary embodiment, screw 228 includes a threaded shank 230, which is about 0.13 inches in diameter and 0.22 inches long. A beveled collar 232 is formed at an angle of about 30 degrees from the axis of the screw. A cylindrical band 234 having a diameter of about 0.26 inches adjoins the tapered collar, and an inwardly tapered outer end 236 is formed at the end of the screw. A hex drive opening 238 is formed in the end of the screw for rotating the screw.

The screw fits in a hole 239 having a tapered opening that mates with tapered collar 232. When the screw first enters the hole, the screw threads permit some sideways movement of the screw in the hole but as the screw advances further into the hole, the hole draws the screw into more fixed axial alignment with the hole. When the tapered screw collar engages the tapered opening in the hole, the band on the screw is brought tightly into holding engagement with the side of the blade. Thus, an out of round or cam type of screw connection is not required in this embodiment. To further improve the blade holding power of the screw, the hole can be at a slight angle, so that the collar on the screw is brought into increasingly tight contact with the side of the blade as the screw is advanced into the hole.

Another feature of this embodiment is the tip drill 240 that fits in an opening 242 in the end of the drill. Tip drill 240 has a shank 244, which has an inclined locking surface 246 thereon. A set screw 248 extends at an angle through a threaded hole in the body, such that an end of the set screw bears against the inclined locking surface and urges the shank of the tip drill axially inwardly into the opening in the drill body so as to tighten the engagement of the tip drill in the drill body as the set screw is tightened. The tip drill has a cutting surface and step on the outer end 250 thereof that mates with the steps of the drill formed along the head of the drill body and the outer end of the replacement blade.

In operation, step drill 200 operates in the same manner as the previous embodiments.

The eighth embodiment 300 of the present invention is one of the preferred embodiments, and is shown in FIGS. 25-35. Unibit 300 includes a body 302 and a replacement blade 304. The body includes a shaft 308 at one end 309 and a conical head 310 at a second end 307 of the body, all as in the prior embodiments. Conical head 310 has an inclined outer surface. In the illustrated embodiment, the outer surface is generally smooth and straight. The outer surface, however, could have the steps and flats of prior embodiments, such as steps and flats 32 and 34 of the FIG. 1 embodiment. Providing steps and flats in the body increases the expense of the product and the unibit works without steps and flats in the head. However, the steps and flats seem to improve the smoothness of the operation of the unibit by facilitating the orientation and advancement of the unibit in the drilled hole and by reducing any tendency of the blade to bind in the hole.

Shaft 308 includes flattened portions 316 spaced around the periphery of the shaft for non-rotatably mounting the shaft in a driver chuck. The unibit body 302 can include an enlarged rim 312 at a base 314 of the conical head 310 to prevent the drill from passing all the way through an opening in sheet material. The enlarged rim is optional and may not be employed in all circumstances.

Head 310 has an axially extending slot 355 therein that extends laterally all the way through the cone substantially from the tip to the base of the head and has open sides at the inclined surfaces on both sides of the head. The head on both sides of the slot forms spaced blade support members 354, which are connected to one another and to the shaft 308 at the base 314. Each blade support member is generally triangular in shape, having two long legs 356 and one short leg 358, and the blade support members are positioned so that the replacement blade can be slid into the slot 355 between the blade support members. The long legs 356 of each blade support member 354 are curved outwardly where the blade support member attaches to the base. This curved end 357 directs metal shavings radially outwardly from the tool. Where the long legs of each prong join at the tip end 307, the prong tips 360 may be blunted to ensure that a tip drill 306 on the blade extends beyond the head.

The replacement blade 304 is a generally triangular shaped plate member that is constructed of a suitably hard material, such as 6264 tool steel, for example. In the eighth embodiment, the blade 304 can include an integral tip drill 306 at a tip end 309 of the blade and a base 314 that is positioned adjacent the shaft 308. The blade 304 has two long legs 318 and a short leg 320. The two long legs 318 join at the tip drill 306, which is formed integrally with the blade when a tip drill is desired. There are some instances where a tip drill is not desired, so the blade also can be formed without a tip drill 306. In such a case, the blade ends at blunt end 309 as shown in phantom in FIG. 32. The tip drill 306 has a sharpened drill point 352 for starting a drill hole. Each of the long legs 318 of the blade 304 forms an inclined outer edge of the blade. Each of these legs 318 has a stepped cutting edge 322 that is defined by a series of flats 324 and ramps 325. In use, the head 310 and blade 304 will be rotated and the blade cutting edges 322 will be along the leading face or surface 328 of the blade, relative to the direction of rotation. Each cutting edge 322 of the replacement blade 304 may include a groove 326 adjacent and parallel to the leading edge of the blade. This groove improves the operation of the blade.

The blade 304 includes two aligned blade holes 344 that are generally positioned along the axis of the blade and the blade holder body when the blade 304 is installed in the head 310. The blade holes 344 align with the head holes 342 when the blade is installed in the head. The base or short leg 320 of the blade 304 includes a slot 346 that is generally along the axis “A” when the blade is installed in the head. A pin 348 extends through and is wedged or otherwise secured in hole 350 that extends through the conical head and the slot in the head of the drill body to provide proper positioning of the replacement blade. The slot also makes it easier to replace a blade simply by removing screws 330 and sliding the blade 304 out of the head 310.

The flats 324 are generally parallel with the reference axis “A” when the blade 304 is installed in the head 310, and are spaced a progressively increasing distance from the axis. The ramps 325 of the replacement blade extend between adjacent flats. The tip drill 306, flats 324 and ramps 325 of the blade extend outward from the head 310. Thus, the cutting edges are exposed to do their job of cutting, while the head is a foundation for the blade and holds and positions the blade.

The replacement blade 304 is held in position by means of clamping screws 330 (similar to FIGS. 16 and 17). In an exemplary embodiment, each screw 330 includes a threaded shank 332, which is about 0.13 inches in diameter and is long enough to engage the threads of both holes 342 without protruding beyond the body so as to interfere with or impair the shaving achieved by the blade. A beveled collar 334 is formed at an angle of about 30 degrees from the axis of the screw. A cylindrical band 336 having a diameter of about 0.26 inches adjoins the beveled collar, and an inwardly tapered outer end 338 is formed at the end of the screw. A hex drive opening 340 is formed in the end of the screw for rotating the screw.

The screws 330 fit in holes 342. The screws 330 fit through the holes 342 in the near side of the head, extend through blade holes 344 in the blade 304, and then are threaded into threaded holes 342 in the opposite side of the head.

In operation, step drill 300, which is one of the preferred embodiments, operates in the substantially the same manner as the previous embodiments but provides simplified construction, an integral tip drill (when desired) and secured mounting.

One having ordinary skill in the art and those who practice the invention will understand that various modifications and improvements may be made without departing from the disclosed inventive concept. Various relational terms, including left, right, front, back, top, and bottom, for example, are used in the detailed description of the invention and in the claims only to convey relative positioning of various elements of the claimed invention and are not otherwise used to limit the scope of the invention.