Abstract:
A bevel gear manufacturing face cutter head ( 2 ) for face hobbing and face milling wherein the face cutter head includes a positive blade seating and stick-type rectangular or square cross-section cutting blades ( 6 ) are clamped tight to the positive seating surfaces ( 14, 18 ). The cutting blades are adjustable radially by axial movement by a non-self-locking system.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to cutting tools for gears and in particular to face cutters having a cutter head with stick-type cutting blades and means to clamp the cutting blades in the cutter heads. 
     BACKGROUND OF THE INVENTION 
     Bevel and hypoid gears can be cut in a single indexing process (face milling) or in a continuous indexing process (face hobbing). A basic cutting setup in the generating or cradle plane will put the center of the cutter head in a position which is away from the generating gear center (cradle axis) by the amount of the so-called radial distance. The silhouette of the cutter blades represents one tooth of the generating gear while the cutter rotates). Common face cutters for bevel gear cutting have several blade groups with each group having between one and four blades. Most common types of face cutters are alternating (completing) cutters with one outside and one inside blade. 
     In most stick blade cutter systems, the cutting blades have a rectangular blade cross section are usually secured in a cutter head via a friction seating between clamp blocks or clamp screws and a radial seating surface of the cutter head. An example of positive blade seating is shown in U.S. Pat. No. 6,120,217 which incorporates a pentagon shaped cross section with two specially oriented seating surfaces. It is very important for cutting blade (especially if the blade material is carbide) to achieve a stiff and precise seating between the blades and the cutter head. One purpose of a clamping system is the precise positioning and a high seating stiffness of cutting blades without any blade movements during a tool life run which, for example, may be more than 8 hours of continuous gear cutting. 
     There are some known types of cutter systems with positive blade seating which have found limited industrial utilization. Included in these cutter systems are those utilizing blades with circular or half circle shaped cross sections (for example, U.S. Pat. No. 5,934,841 and EP 1240966 A2). Tapered wedge clamp combinations are used in those systems to press the cylindrical blade sticks into round holes oriented around the circumference of the cutter head body. US 2011/0164931 uses a complex differential tandem wedge to clamp blades with a rectangular cross section into the corner of a rectangular cutter head slot. In the above cases, round or rectangular, the blades are wedged into the seating surfaces with self-locking clamp components. Truing requires tapping with a hammer in order to release the wedges and free the blades for axial movement. Precise cutter head building requires the ability to relieve the clamping forces of the clamping system without disturbing the axial blade location in order to move the blades axially by small amounts relative to their previous position. Such a truing procedure is not possible with self- locking systems wherein impacts from a tool, such as a hammer or screwdriver for example, are required before a blade can be axially moved. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a bevel gear manufacturing face cutter head for face hobbing and face milling wherein the face cutter head includes a positive blade seating and stick-type rectangular or square cross-section cutting blades are clamped tight to the positive seating surfaces. The cutting blades are adjustable radially by axial movement by a non-self-locking system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1( a )  shows a cross section of a cutter head with a stick blade which is connected to the cutter head with a clamp block and one clamp screw.  FIG. 1( b )  shows a similar cross section but with the clamp block pressed against the blade with two clamp screws. 
         FIG. 2  shows to top view onto a section of a cutter head. The stick blade is pressed from a single screw and a clamp block onto the radial seating surface 
         FIG. 3  shows a three dimensional view of a cutter head section with a rectangular stick blade pressed with two clamp screws and a clamp block onto the radial seating surface. The connection between blade and cutter head is a friction seating. 
         FIG. 4  shows a top view onto a cutter head section with one rectangular slot. The stick blade in the slot is pressed by two corner screws and an angular clamp block against the tangential and radial seating surfaces. 
         FIG. 5  shows a three dimensional view of a cutter head section with one blade slot. The rectangular blade is pressed with one corner screw and an angular clamp block against the tangential and the radial seating surfaces. 
         FIG. 6  shows a three dimensional view of a cutter head section with one blade slot. The rectangular blade is pressed with two corner screws and an angular clamp block against the tangential and the radial seating surfaces. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The terms “invention,” “the invention,” and “the present invention” used in this specification are intended to refer broadly to all of the subject matter of this specification and any patent claims below. Statements containing these terms should not be understood to limit the subject matter described herein or to limit the meaning or scope of any patent claims below. Furthermore, this specification does not seek to describe or limit the subject matter covered by any claims in any particular part, paragraph, statement or drawing of the application. The subject matter should be understood by reference to the entire specification, all drawings and any claim below. The invention is capable of other constructions and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purposes of description and should not be regarded as limiting. 
     The details of the invention will now be discussed with reference to the accompanying drawings which illustrate the invention by way of example only. In the drawings, similar features or components will be referred to by like reference numbers. 
     The use of “including”, “having” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order. 
     Although references may be made below to directions such as upper, lower, upward, downward, rearward, bottom, top, front, rear, etc., in describing the drawings, there references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally or limit the present invention in any form. In addition, terms such as “first”, “second”, “third”, etc., are used to herein for purposes of description and are not intended to indicate or imply importance or significance. 
       FIG. 1( a )  shows a cross sectional view of a cutter head  2  having a top surface  3 , a bottom surface  4  and a blade positioning slot  5  (see  FIG. 2 ) and further including a stick blade  6  which is positioned and held in the cutter head  2  with a clamp block  8  and one clamp screw  10  or an equivalent means to exert a force on clamp block  8 . The blade  6  is pressed against the radial seating surface  14 . The main cutting force is perpendicular to the clamp force. The friction between the seating surface  14  and the blade  6  should prevent the blade from moving perpendicular the drawing plane. Due to the intermitted cutting forces and tolerances on the flatness of the contacting surfaces of cutter head  2  and blade  6 , an initial blade movement can occur. Such a movement slides the blade  6  perpendicular to the drawing plane until the back side of the blade contacts the back side of the slot  5 . 
       FIG. 1( b )  shows a similar cross section of a cutter head  2  with a rectangular stick blade  6 . In this drawing the clamp block  8  is pressed against the blade  6  with two clamp screws  10 ,  12 . 
       FIG. 2  shows to top view onto a section of a cutter head  2 . The stick blade  6  is pressed from a single screw  10  and a clamp block  8  onto the radial seating surface  14 . A gap  16  which is required in order to allow the placing of a blade  6  in the slot  5  is shown in front of the blade  6 . As a result of cutting, the gap will be partially in the front of the blade and partially between the back of the blade and the tangential seating surface  18 . It is very likely the gap will exist in the front of the blade at the top of the cutter and in the back of the blade at the bottom of the cutter. Between the top and bottom of the cutter, the gap will be partially in the front and partially in the back of the cutting blade  6 . This type of seating principle is known as “friction seating” since no clamp force component exists which would press the blade  6  against the tangential seating surface  18 . The tangential seating surface  18  is therefore not a qualified seating surface. Dynamic cutting forces can change the split of gap components between front and back continuously during the cutting process. 
       FIG. 3  shows a three dimensional view of a cutter head section with a rectangular stick blade  6  pressed with two clamp screws  10 ,  12  and a clamp block  19  onto the radial seating surface  14 . The connection between blade  6  and cutter head  2  is a friction seating. The main cutting force direction is perpendicular to the clamping force. Only the friction between radial seating surface  14  and blade  6  prevent the blade from a tangential movement. 
     The inventor has developed a bevel gear cutter head having stick-type cutting blades with a rectangular or square cross section and a blade clamping mechanism which provides a stiff positive seating of the stick blades in the cutter head slots of both face milling and face hobbing cutters. 
       FIG. 4  shows a top view onto a face milling cutter head section with one rectangular slot  5  illustrated. The stick blade  6  in the slot is pressed by two corner screws  10 ,  12  and an “L-shaped” angular clamp block  20  against at least a portion of both the tangential seating surface  18  and the radial seating surface  14 . The radial seating surface  14  provides a precise and stiff radial positioning of the blade  6  while the tangential seating surface  18  backs the blade up against the main cutting force with a high contact stiffness. The clamp screw  10  is oriented under an angle γ (with respect to a reference line perpendicular to radial seating surface  14 ) on the front outside corner of the cutting blade, its force F 1  acts with the F 1a  component radially and with the F 1b  component tangentially as shown in  FIG. 4 . The force F 2  of a similarly positioned lower second clamp screw  12  acts also with the F 1a  component radially and with the F 2b  component tangentially (not shown in  FIG. 4 ). The seating principle is a positive seating or form seating. 
       FIG. 5  shows a three dimensional view of a cutter head section with one blade slot  5  illustrated. The rectangular blade  6  is pressed with one corner screw  10  and an L-shaped angular clamp block  22  against at least a portion of both the tangential seating surface  18  and the radial seating surface  14 . The stiff tangential seating provides high blade stiffness in the cutting process and prevents blade vibrations. The stiff radial seating provides a precise blade location and also prevents blade movement and vibrations during the gear cutting process. 
       FIG. 6  shows a three dimensional view of a cutter head section with one blade slot  5  illustrated. The rectangular blade  6  is pressed with two corner screws  10 ,  12  and an angular clamp block  22  against the tangential seating surface  18  and the radial seating surface  14 . Depending on the design of the clamp block  22  and the clamping length of the blade  6 , it can be an advantage to use a second clamp screw. In such a case, the upper clamp screw  10  may be located with some distance to the upper face  3  of the cutter head  2  and the lower clamp screw  12  might be located at the lowest possible point relative to the clamp block  22 . 
     The inventive cutter head uses stick blades with square or rectangular blade cross section. With respect to the direction of cutter rotation, the clamp block  22  preferably contacts at least a portion of the front surface  24 , at least a portion of the outside surface  26  and the blade corner  28  defined by the intersection of the front and outside surfaces (as defined by a cutting blade positioned in a cutter head illustrated by  FIGS. 4-6 ). The clamp block  22  extends longitudinally by a distance not exceeding the length of the slot  5  between the top surface  3  and the bottom surface  4 . One or more clamp screws  10 ,  12  are positioned to contact the corner area, preferably a flat area  30 , of the clamp block  22  and are oriented under an appropriate angle γ (e.g. 45°) to the reference line perpendicular to radial seating surface  14  (see  FIG. 4 ). The radial clamp force F 1a  component presses the stick blade  6  against the radial seating surface  14  and provides precise positioning as well as radial seating stiffness. The tangential force component F 1b  presses the stick blade  6  against the tangential seating surface  18  and provides a defined position and a stiff seating of the blade in tangential direction. The main cutting force direction finds a reaction force coming from the tangential seating surface without tangential blade movement and dynamic disturbances. The inventive seating arrangement provides a positive blade seating between square or rectangular stick blades and a cutter head. 
     As can be seen in  FIGS. 4-6 , when a cutting blade  6  is positioned in a blade positioning slot  5  of a cutter head  2 , three of the blade corners are located next to one or both of the radial seating surface  14  and the tangential seating surface  18 . The fourth blade corner  28 , defined by the intersection of the blade front surface  24  and the outside surface  28  (with respect to the direction of cutter rotation) is therefore defined as the front outside corner and is located remote from both the radial seating surface  14  and the tangential seating surface  18 . A clamping force, F 1 , oriented at an angle γ to the reference line of the slot  5 , is applied by one or more clamping screws (e.g.  10  and/or  12 ), preferably via a clamp block  20 ,  22 , which applies the clamping force to the front outside (i.e. remote) corner  28 . Alternatively, the clamping force may be applied to an area of the blade front surface  24  and/or the outside surface  28  located near to the corner  28  (i.e. the “remote corner region”) of the cutting blade. 
     The clamp screw angle γ may be lower than 45° in order to have high radial seating contact force and generate, in the tangential direction, just enough force to get a defined and stiff seating on the tangential seating surface  18 . The main cutting force vector F 1  will deliver an additional force against the tangential seating surface  18  in the upper area. The main cutting force will also try to separate the tangential seating surface  18  in the lower area of the slot  5 . The tangential pressure component (from one or more clamp screws) in the lower area acts to prevent the surface separation in this area. In case of two clamp screws (e.g.  10 ,  12 ), it is also possible to use a lower torque on the top clamp screw  10  and a higher torque on the lower clamp screw  12  or vice versa. 
     Controlling different radial and tangential force components of the upper and lower clamp screw may be accomplished by the use of different angular orientations of the upper and lower clamp screws  10 ,  12 . For example, the upper clamp screw  10  may have a more radial orientation (e.g. γ 1 =30°) and the lower clamp screw  12  may have a more tangential orientation (e.g. γ 2 =60°). In case of a chosen angle γ, the force components of F 1  which act onto the two seating surfaces  14 ,  18  are:
 
F 1a =F 1  cos γ 1  
 
F 1b =F 1  sin γ 1  
 
F 2a =F 2  cos γ 2  
 
F 2b =F 2  sin γ 2  
 
     The illustration in  FIG. 4  indicates γ=γ 1 =γ 2    
     In  FIG. 4  only the upper clamp screw  10  is visible. Clamp screw  12  (Force=F 2 , clamp screw angle=γ 2 ) is located below the upper clamp screw  10  and is hidden in the view of  FIG. 4 . 
     For ease of understanding and explanation of the invention, the Y-axis of the coordinate system in  FIGS. 5 and 6  has been chosen parallel to the cutter head axis of rotation and the extension of the Z-axis to the left (negative direction) intersects with the cutter head axis of rotation. The theoretical blade front is oriented in the plane which is defined by the Y and Z axes. Although stick blades in actual cutter heads are commonly inclined with their length direction versus the Y-axis and have an offset with their theoretical front face versus the Z-axis, the principle function of the adjustment will not change and the resulting blade tip position and angle changes will only differ in the single percent range if actually realized cutter head designs are considered. 
     The inventive clamping system is also applicable to those cutters which do not utilize clamp blocks. The clamp screws of those cutters types usually include a provision for a rotating tip (e.g. swivel head) or blades with a flat area perpendicular to the clamp screw axis in order to provide a surface for defined and stable contact between the tip of a clamp screw and a stick blade. 
     While the invention has been described with reference to preferred embodiments it is to be understood that the invention is not limited to the particulars thereof. The present invention is intended to include modifications which would be apparent to those skilled in the art to which the subject matter pertains without deviating from the spirit and scope of the appended claims.