Patent Description:
Rotary cutting tools can be provided with a threaded coupling mechanism, or "tool joint", for securely retaining a replaceable cutting head within a tool holder.

The replaceable cutting head can include a male coupling member and the tool holder can include a female coupling member. The male coupling member can include an external thread. The female coupling member can include an internal thread that corresponds to the external thread on the male coupling member.

In some such rotary cutting tools, the internal and external threads are both straight threads. An example of such a rotary cutting tool is disclosed in, for example, <CIT>.

In other such rotary cutting tools, the internal and external threads are both tapered threads. Examples of such a rotary cutting tool are disclosed in, for <CIT>, <CIT> and <CIT>.

<CIT> describes a coupling mechanism for a cutting tool.

In accordance with a first aspect of the subject matter of the present application there is provided a rotary cutting tool according to the features of claim <NUM>.

In accordance with another aspect of the subject matter of the present application there is provided a tool holder according to the features of claim <NUM>.

It is understood that the above-said is a summary, and that features described hereinafter may be applicable in any combination to the subject matter of the present application, for example, any of the following features may be applicable to the rotary cutting too and/or the tool holder:.

The cone angle can be equal to exactly <NUM>°.

Only the internal thread groove can extend about a respective cone.

In a cross-sectional view taken in an axial plane containing the internal thread axis, the internal top surface forms a plurality of internal thread crests that can be parallel to the internal thread axis and co-linear with each other and the internal bottom surface forms a plurality of internal thread roots are parallel to the internal thread axis and follow a pattern of decreasing distance therefrom in the rearward direction.

The forward and rearward internal flank surfaces are offset from the internal thread axis by a distance that can decrease as the internal ridge extends helically about the internal thread axis in the rearward direction.

The external thread comprises an external thread ridge, extending helically about an external thread axis, and comprising forward and rearward external flank surfaces and an external top surface extending therebetween, the forward and rearward external flank surfaces generally face in opposite axial directions and delimit a helical external thread groove that comprises an external bottom surface;
the forward external flank surface and the forward internal flank surface face in the forward direction and the rearward external flank surface and the rearward internal flank surface face in the rearward direction; and in the locked position:
the rearward internal flank surface can abut the forward external flank surface.

In the locked position the forward internal flank surface can be spaced apart from the rearward external flank surface. The internal top surface can be spaced apart from the external bottom surface. The internal bottom surface can be spaced apart from the external top surface.

In a cross-sectional view taken in an axial plane containing the external thread axis, the external top surface forms a plurality of external thread crests that can be parallel to the external thread axis and co-linear with each other and the external bottom surface forms a plurality of external thread roots that are parallel to the external thread axis and co-linear with each other.

In a cross-sectional view taken in an axial plane containing the head longitudinal axis, the external thread defines an external thread form that can be trapezoidal.

In a cross-sectional view taken in an axial plane containing the holder longitudinal axis, the internal thread defines an internal thread form that can be trapezoidal.

The external thread comprises an external thread ridge, extending helically about an external thread axis, and comprising forward and rearward external flank surfaces and an external top surface extending therebetween;.

For a better understanding of the present application and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings, in which:.

For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity, or several physical components may be included in one functional block or element. Where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

In the following description, various aspects of the subject matter of the present application will be described. For purposes of explanation, specific configurations and details are set forth in sufficient detail to provide a thorough understanding of the subject matter of the present application. However, it will also be apparent to one skilled in the art that the subject matter of the present application can be practiced without the specific configurations and details presented herein.

Attention is first drawn to <FIG> showing a rotary cutting tool <NUM> of the type used for milling operations, specifically fast face milling, in accordance with embodiments of the subject matter of the present application. The rotary cutting tool <NUM> has a tool longitudinal axis L around which the tool rotates in a direction of rotation R.

The rotary cutting tool <NUM> includes a replaceable cutting head <NUM> that has a head longitudinal axis A, around which the replaceable cutting head <NUM> rotates in the direction of rotation R. The head longitudinal axis A extends in the forward DF to rearward direction DR. The replaceable cutting head <NUM> can be typically made from cemented carbide.

The rotary cutting tool <NUM> also includes a tool holder <NUM> having a holder longitudinal axis C. The tool holder <NUM> can be typically made from steel. The replaceable cutting head <NUM> can be removably retained in the tool holder <NUM> by means of a threaded coupling mechanism. Such a threaded coupling mechanism could possibly be advantageous for other types of rotary cutting operations than that stated hereinabove, such as, for example, reaming or drilling.

It should be appreciated that use of the terms "forward" and "rearward" throughout the description and claims refer to a relative position of the replaceable cutting head <NUM> to the tool holder <NUM> of the assembled rotary cutting tool <NUM>, as seen in <FIG>. The terms "forward" and "rearward" may also be applied in a direction of the head longitudinal axis A towards the left and right, respectively, in <FIG>, and also in a direction of holder longitudinal axis C towards the left and right, respectively, in <FIG>.

Reference is now made to <FIG>. The replaceable cutting head <NUM> has a forward portion that forms a cutting portion <NUM> and a rearward portion that forms a mounting portion <NUM>. In accordance with some embodiments of the subject matter of the present application the replaceable cutting head <NUM> can be formed from a unitary integral one-piece construction. This provides an advantage in that the replaceable cutting head <NUM> has no detachable cutting inserts (not shown).

Referring to <FIG>, the cutting portion <NUM> includes at least one peripheral cutting edge <NUM>. In this non-limiting example shown in the drawings there can be exactly two peripheral cutting edges. Each peripheral cutting edge <NUM> is formed at the intersection of a peripheral relief surface <NUM>, and a peripheral rake surface <NUM>. The peripheral relief surface <NUM> is located rotationally behind the peripheral cutting edge <NUM> and the peripheral rake surface <NUM> is located rotationally ahead of the peripheral cutting edge <NUM>, both in respect to the direction of rotation R. The orientation of the peripheral cutting edge <NUM> allows metal cutting operations to be performed.

In accordance with some embodiments of the subject matter of the present application the cutting portion <NUM> can include at least one flute <NUM> for evacuating chips (not shown) that are produced during the cutting operation. One flute <NUM> is associated to each peripheral cutting edge <NUM>. The replaceable cutting head <NUM> can include one or more end cutting edges 30b at an end face <NUM> of the cutting portion <NUM>. In this non-limiting example shown in the drawings, the replaceable cutting head <NUM> can include exactly two end cutting edges 30b. Each of the two end cutting edges 30b may have an associated side cutting edge 30a.

Making reference now to <FIG>, the mounting portion <NUM> includes a male coupling member <NUM> that protrudes rearwardly from a head base surface <NUM>. The head base surface <NUM> extends transversely with respect to the head longitudinal axis A and defines a boundary between the cutting portion <NUM> and the mounting portion <NUM>. That is to say, the cutting portion <NUM> is formed forward of the head base surface <NUM> and the mounting portion <NUM> is formed rearward of the head base surface <NUM>. In accordance with some embodiments of the subject matter of the present application the male coupling member <NUM> can be rigid. The head base surface <NUM> can be perpendicular to the head longitudinal axis A. The head base surface <NUM> is intended to abut a corresponding surface on the tool holder <NUM> when the rotary cutting tool <NUM> is in a locked position, as will be described hereinafter.

The male coupling member <NUM> includes an external thread <NUM>. Referring to <FIG>, the external thread <NUM> includes an external thread ridge <NUM> that extends helically about an external thread axis B. The external thread axis B is co-incident with the head longitudinal axis A. Thus, the external thread portion <NUM> and the replaceable cutting head <NUM> are co-axial. The external thread ridge <NUM> includes forward and rearward external flank surfaces <NUM>, <NUM> and an external top surface <NUM> that extends therebetween. The forward and rearward external flank surfaces <NUM>, <NUM> face in opposite axial directions DF, DR, with the forward external flank surface <NUM> facing in the forward direction DF and the rearward external flank surface <NUM> facing in the rearward direction DR. The forward and rearward external flank surfaces <NUM>, <NUM> delimit an external thread groove <NUM>. The external thread groove <NUM> extends helically about the external thread axis B and includes an external bottom surface <NUM>.

In a cross-sectional view taken in an axial plane (that is, a plane that contains the external thread axis B) the external top surface <NUM> forms a plurality of external thread crests <NUM> and the external bottom surface <NUM> forms a plurality of external thread roots <NUM>. In accordance with some embodiments of the subject matter of the present application, the plurality of external thread crests <NUM> can be parallel to the external thread axis B and co-linear with each other. The plurality of external thread roots <NUM> can be parallel to the external thread axis B and co-linear with each other.

In a cross-sectional view taken in an axial plane containing the external thread axis B, the forward and rearward external flank surfaces <NUM>, <NUM> can be inclined at an external flank angle α with respect to a radial plane perpendicular to the external thread axis B. Preferably, the external flank angle α can be around <NUM>°. The external thread <NUM> defines an external thread form <NUM> that can be trapezoidal. The external top surface <NUM> and external bottom surface <NUM> can smoothly transition into the forward and rearward external flank surfaces <NUM>, <NUM>, respectively, defining a radius. Alternatively, the external thread form <NUM> can be triangular.

The external top surface <NUM> and external bottom surface <NUM> can form an edge. The plurality of external thread crests <NUM> define the major diameter and the plurality of external thread roots <NUM> define the minor diameter of the external thread <NUM>, respectively. The major diameter minus the minor diameter, divided by two, equals the external thread height HE of the external thread <NUM>. The external thread height HE can be constant. In accordance with some embodiments of the subject matter of the present application, the external thread <NUM> can have approximately three turns.

The external thread <NUM> is a straight thread. It should be appreciated that the term "straight thread" throughout the description and claims relates to a thread where the thread ridge extends about a cylinder and thus the thread crests are equidistant from the thread axis. Similarly, it should be appreciated that the term "tapered thread" throughout the description and claims relates to a thread where the thread ridge extends about a cone, whose surface tapers radially inwardly towards the thread axis in the rearward direction, and thus the thread crests decrease in distance from the thread axis in the rearward direction.

As shown in <FIG>, the male coupling member <NUM> includes a forward bearing portion <NUM>. The forward bearing portion <NUM> is located on the forward side of the external thread <NUM>. The forward bearing portion <NUM> includes a forward head abutment surface <NUM> that tapers radially inwardly towards the head longitudinal axis A in a rearward direction DR. That is to say, the forward head abutment surface <NUM> has a conical shape facing radially outwards. It is noted that the forward head abutment surface <NUM> is intended to abut a corresponding surface on the tool holder <NUM> when the rotary cutting tool <NUM> is in a locked position, as will be described hereinafter.

It should be appreciated that use of the terms "radially inward/inwardly" and "radially outward/outwardly" throughout the description and claims refer to a relative position in a perpendicular direction in relation to the head longitudinal axis A and/or holder longitudinal axis C, towards and away from the respective axis, in <FIG> and <FIG>.

Referring now to <FIG>, the tool holder <NUM> has a holder longitudinal axis C that extends in the forward DF to rearward direction DR. The tool holder <NUM> includes a female coupling member <NUM> that extends rearwardly from a holder forward surface <NUM>. The holder forward surface <NUM> extends transversely with respect to the holder longitudinal axis C. In accordance with some embodiments of the subject matter of the present application the holder forward surface <NUM> can be perpendicular to the holder longitudinal axis C.

The female coupling member <NUM> includes an internal thread <NUM>. As shown in a longitudinal cross-sectional view of the female coupling member <NUM> containing the internal thread axis D (i.e. <FIG>), the internal thread <NUM> includes an internal thread ridge <NUM> that extends helically about an internal thread axis D. The internal thread axis D is co-incident with the holder longitudinal axis C. Thus, the internal thread portion <NUM> is co-axial with the tool holder <NUM>. The internal thread ridge <NUM> includes forward and rearward internal flank surfaces <NUM>, <NUM> and an internal top surface <NUM> that extends therebetween. The forward and rearward internal flank surfaces <NUM>, <NUM> face in opposite axial directions DF, DR, with the forward internal flank surface <NUM> facing in the forward direction DF and the rearward internal flank surface <NUM> facing in the rearward direction DR. The forward and rearward internal flank surfaces <NUM>, <NUM> delimit an internal thread groove <NUM>.

The internal thread groove <NUM> extends helically about the internal thread axis D and includes an internal bottom surface <NUM>. In a cross-sectional view taken in an axial plane (that is, a plane that contains the internal thread axis D) the internal top surface <NUM> forms a plurality of internal thread crests <NUM> and the internal bottom surface <NUM> forms a plurality of internal thread roots <NUM>. The plurality of internal thread crests <NUM> are parallel to the internal thread axis D and co-linear with each other. The plurality of internal thread roots <NUM> are parallel to the internal thread axis D and follow a pattern of decreasing distance therefrom in the rearward direction DR.

In a cross-sectional view taken in an axial plane containing the internal thread axis (D), the forward and rearward internal flank surfaces <NUM>, <NUM> can be inclined at an internal flank angle β with respect to a radial plane perpendicular to the internal thread axis D. Preferably, the internal flank angle β can be around <NUM>°. The internal thread <NUM> defines an internal thread form <NUM> that can be trapezoidal. Referring now to <FIG>, the sides of the trapezium may not be equal in length. The internal top surface <NUM> and internal bottom surface <NUM> can smoothly transition into the forward and rearward internal flank surfaces <NUM>, <NUM>, respectively, defining a radius. Alternatively, the internal thread form <NUM> can be triangular.

The internal top surface <NUM> and internal bottom surface <NUM> can form an edge. The plurality of internal thread crests <NUM> define the minor diameter and the plurality of internal thread roots <NUM> define the major diameter of the internal thread <NUM>, respectively. The major diameter minus the minor diameter, divided by two, equals the internal thread height HI of the internal thread <NUM>. The internal thread height HI can be constant, or increasing or decreasing in the rearward direction DR depending on which of the internal thread ridge <NUM> and internal thread groove <NUM> extend about a respective cone K In this non-limiting example shown in the drawings, the internal thread height HI decreases in the rearward direction In accordance with some embodiments of the subject matter of the present application, the internal thread <NUM> can have approximately three turns. The internal thread <NUM> is a conical thread. It should be appreciated that the term "conical thread" throughout the description and claims relates to a thread where at least one of the thread ridge and the thread groove extend about a respective cone, whose surface tapers radially inwardly towards the thread axis in the rearward direction, and thus at least one of the thread crests and thread roots decrease in distance from the thread axis in the rearward direction. Such a conical thread may be formed by threading the hollow forward end of a cylindrical steel rod with an internal turning insert. As the steel rod rotates and moves in the axial direction to form the internal thread it also moves radially away from the 'static' cutting insert so that the thread has a conical configuration. The cone and the thread are co-axial. In <FIG>, the cone is defined by the points where the internal bottom surface <NUM> transitions into the rearward internal flank surface <NUM>.

In accordance with some embodiments of the subject matter of the present application, at least one of the internal thread ridge <NUM> and the internal thread groove <NUM> can extend about a respective cone K having a cone angle γ. The cone angle γ is in the range of <NUM>° ≤ γ ≤ <NUM>°. Advantageously, the cone angle γ can be equal to exactly <NUM>°. Only the internal thread groove <NUM> can extend about a respective cone K Moreover, the internal thread ridge <NUM> can extend about a cylinder Y. It should further be appreciated that use of the term "cone angle" throughout the description refers to an angle formed by the tapered surfaces of a cone, in a longitudinal cross-section. It is noted that the term "longitudinal cross-section" refers to a cross-section taken in a plane containing the longitudinal axis. Such a longitudinal cross-section results in an axial plane containing the longitudinal axis.

As shown in <FIG>, the female coupling member <NUM> includes a forward supporting portion <NUM> The forward supporting portion <NUM> is located on the forward side of the internal thread <NUM>. The forward supporting portion <NUM> includes a forward holder abutment surface <NUM> that tapers radially inwardly towards the holder longitudinal axis C in a rearward direction DR. That is to say, the forward holder abutment surface <NUM> has a conical shape facing radially inwards.

Assembly of the rotary cutting tool <NUM> is known, for example, from <CIT>, which is hereby incorporated by reference in its entirety. It is noted that the rotary cutting tool <NUM> is adjustable between a released position and a locked (or assembled) position.

In the released position the male coupling member <NUM> is located outside of the female coupling member <NUM>.

In the locked position the male coupling member <NUM> is removably retained in the female coupling member <NUM>. Also, the external and internal threads <NUM>,<NUM> threadingly engage each other. Referring now to <FIG>, the forward head abutment surface <NUM> abuts the forward holder abutment surface <NUM>. In accordance with some embodiments of the subject matter of the present application, the rearwardly facing head base surface <NUM> can abut the forwardly facing holder forward surface <NUM>. The rearward internal flank surface <NUM> can abut the forward external flank surface <NUM>. The forward internal flank surface <NUM> can be spaced apart from the rearward external flank surface <NUM>. The internal top surface <NUM> can be spaced apart from the external bottom surface <NUM>. The internal bottom surface <NUM> can be spaced apart from the external top surface <NUM>.

Attention is now drawn to <FIG> showing a schematic view of the internal thread form <NUM> of a conical internal thread <NUM>. By means of dashed lines an imaginary internal thread form <NUM> of a straight internal thread and an imaginary external thread form <NUM> of a straight external thread, which are threadingly engaged with each other, are superimposed thereupon. It is noted that the cone angle γ of the internal thread <NUM> that forms the internal thread form <NUM> is exaggerated in order to clearly show the internal thread forms <NUM>, <NUM> in relation to each other, and thus distances do not represent of true values.

Each turn of the internal thread form <NUM> is offset from the thread axis D by a distance that, by virtue of the internal thread <NUM> being conical, decreases as the internal thread <NUM> extends helically about the thread axis in the rearward direction DR. Thus, each ridge portion of the internal thread form <NUM> extends beyond (or stated differently, has a part that "overhangs") a corresponding ridge portion of the imaginary internal thread form <NUM> such that each rearward internal flank surface <NUM> is distanced from the respective imaginary rearward internal flank surface <NUM> by a flank distance E. Moreover, the flank distance E increases in magnitude in the rearward direction DR. That is to say, the flank distance E increases in magnitude for successive thread turns in the rearward direction DR. Similarly, each ridge portion of the internal thread form <NUM> extends over as to partly cover (i.e. overlaps) a corresponding ridge portion of the imaginary external thread form <NUM> such that each rearward internal flank surface <NUM> is distanced from the respective imaginary forward external flank surface <NUM> by the same flank distance E. Thus clearly, when assembled (i.e., threadingly engaged), the frictional engagement between the external thread <NUM> and the internal thread <NUM> increases in a direction from the forwardmost turn of the external thread <NUM> towards the rearmost turn.

Reference is now made to <FIG>, showing four diagrams showing the contact force distribution exerted on straight external threads that are threadingly engaged with straight and conical internal threads, respectively, when the rotary cutting tool is assembled and working. The lengths of the arrows represent the magnitude of the contact forces. It can be seen that the distribution of the contact forces, when the rotary cutting tools <NUM> are assembled and working, on a straight external thread threadingly coupled with a conical internal thread (the two diagrams on the right), are located further in the rearward direction DR compared with a straight internal thread threadingly engaged with a straight internal thread (the two diagrams on the left). In particular, it can be seen that when the rotary cutting tool <NUM> having the conical internal thread is assembled there are hardly any contact forces located at a forward area A1 of the straight external thread. Moreover, when said rotary cutting tool <NUM> is working there are contact forces at a rear area A2 of the straight external thread. By virtue of the foregoing threaded engagement the rotary cutting tool <NUM> has improved stability against lateral cutting forces.

Claim 1:
A rotary cutting tool (<NUM>) having a longitudinal axis (L) and extending in a forward (DF) to rearward direction (DR), comprising:
a tool holder (<NUM>), having a holder longitudinal axis (C) and comprising a female coupling member (<NUM>) having an internal thread (<NUM>) extending rearwardly from a holder forward surface (<NUM>), the holder forward surface (<NUM>) extending transversely with respect to the holder longitudinal axis (C); and
a replaceable cutting head (<NUM>) having a head longitudinal axis (A) and comprising:
a forward portion forming a cutting portion (<NUM>); and
a rearward portion forming a mounting portion (<NUM>), the mounting portion (<NUM>) comprising a male coupling member (<NUM>) having an external thread (<NUM>) and protruding rearwardly from a head base surface (<NUM>), the head base surface (<NUM>) extending transversely with respect to the head longitudinal axis (A), and defining a boundary between the cutting portion (<NUM>) and the mounting portion (<NUM>);
wherein:
the internal thread (<NUM>) of the female coupling member (<NUM>) is conical thread; and
the rotary cutting tool (<NUM>) is adjustable between:
a released position in which the male coupling member (<NUM>) is located outside of the female coupling member (<NUM>), and the internal and external threads (<NUM>, <NUM>) are not threadingly engaged to one another, and
a locked position in which the male coupling member (<NUM>) is removably retained in the female coupling member (<NUM>) with the internal and external threads (<NUM>, <NUM>) threadingly engaged to one another;
characterized in that the external thread (<NUM>) of the male coupling member (<NUM>) is a straight thread.