Machining

4 편 절 삭 가 공

relieving 선반에서 cutter 및 hob의 여유면을 가공하기 위한 bite 다양한 운동기구의 예
cutter의 relieving 방법	relieving lathe
(1) Lathe Attachment for Relieving
An ingenious lathe attachment for backing off the teeth of milling cutters is shown in the above figure. In a device of this character either the tool or the work must be given a slight in-and-out motion for each tooth on the cutter being relieved. In the case shown, the tool is held in the tool post and advanced to its cut in the ordinary manner. The mandrel A of the attachment has its centers slightly eccentric, the amount of the eccentricity being enough to produce the desired amount of relief on one tooth of the cutter if mounted directly on the mandrel. The arm L is secured to the mandrel and driven from the face-plate by the carrier D. The sleeve B, which carries the cutter being operated upon, revolves freely upon the mandrel. The gear b is secured to the sleeve and the gear a is loose on the sleeve, and is held from rotating by the arm d which is secured to it and rests upon the top of the tool t. Pinion c is carried loose on the stud D and gears with a and b. Gear b has a smaller number of teeth than a, and as a does not rotate, the rotation of the pinion c around a advances b and the sleeve and cutter a certain fixed amount at each revolution of the mandrel. The geared ratio is such for any given number of teeth in the cutter that the advance per revolution is exactly equal to the circular pitch of the teeth in the cutter. The turning is such as to bring a tooth to the tool when the center of the mandrel is farthest from the tool, thus giving the relief as the tooth advances to the tool. It is evident from the above that the space between the teeth must be at least equal to the length of the tooth. As this division of space and tooth in relieved milling cutters is not usual, it is necessary to allow the cutter blank to stand still while the mandrel is moving though a part of its revolution. This is accomplished by making the circular pitch of the teeth on about one-half the circumference of b equal to that of the teeth on a and the the teeth on the balance of b of somewhat greater circular pitch. For that portion where the teeth are the same on a and b , the pinion simply turns around both and the sleeve remains stationary. During the balance of the revolution, however, the sleve will advance an amount equal to the circular pitch of the cutter's tooth.
(2) Milling Cutter Nomenclature OUTSIDE DIAMETER. The outside diameter is the diameter of the cylinder passing through the peripheral cutting edges. ROOT DIAMETER. The root diameter is the diameter of the circle passing tangent to the bottom of the fillet. SIDE TOOTH LENGTH. Length of the raised land along the side tooth. Required to calculate the number of resharpenings available and the modification possibilities. CUTTER FACE WIDTH. The cutter face is the surface at the side or end of the cutter body which is perpendicular to the axis of the cutter. The distances between the two faces of plain, helical and side milling cutters, or the length of the outside diameter cylinder is the cutter width, if small, or cutter length,with respect to the diameter. TOOTH FACE. The tooth face is that surface of the cutting tooth against which the chip is forced in the metal cutting operation. LAND. The land is that part of the back of the tooth adjacent to the cutting edge which is relieved to avoid interference between itself and the surface being machined. A raised land permits numerous resharpenings before a secondary clearance has to be ground. CUTTING EDGE. The cutting edge is the intersection of the face of the tooth with the leading edge of the land. FLUTE. The flutt, is the chip space between the back of one tooth and the face of the following tooth. RELIEF ANGLE. The peripheral relief angle is the angle between the surface formed by the land and a tangent to the cutter outside circle passing through the cutting edge in a diametral plane. It is to prevent the land from rubbing on the surface of the work being cut. Relief and clearance are measured in degrees or in radial fall in inches at a certain specified distance back of the cutting edge on the land. For this latter measurement, a dial indicator may be used to measure the radial fall in thousandths of an inch from the outside or cutting edge diameter back of the cutting edge. RADIAL RAKE ANGLE. The radial rake angle of a milling cutter is the angle formed in a diametral plane between the face of the tooth and a radial line passing through the cutting edge. This may be positive, negative, or zero degree. AXIAL RAKE ANGLE OR HELICAL RAKE. When a milling cutter has helical teeth, that is, when its cutting edge is formed along a helix about the cutter axis, the resulting rake is called helicall rake. If the cutting edge is straight, its rake is axial rake. The axial rake or helical rake angle is the angle formed between the line of the peripheral cutting edge and the axis of the cutter, when looking radially at the point of intersection. This applies in the case of helical mills, half-side mills, staggered tooth mills, face mills, and metal slitting saws having face cutting edges. GASH DEPTH. Gash depth is the distance from the outside diameter of the cutter to the fillet radius or root diameter. FILLET RADIUS. The fillet radius is the curved surface at the bottom of the flute which joins the face of one tooth to the back of the tooth immediately ahead. DISH OR CONCAVITY. The progressive decrease in cutter width from the periphery toward the center. RADIAL OFFSET. The radial offset of a milling cutter is the physical dimension that a tooth is behind(for positive rake) or ahead (for negative rake) of a center line drawn parallel with flat, tooth face. It is calculated by multiplying the sine function of the radial rake angle times the radius of the milling cutter. DEPTH OF RECESS. The distance from the cutting edge on the land of the side tooth (or the hub which is the same width as the cutter) to the recess is the depth of recess. This dimension is required to determine width and angle modification limits. HUB DIAMETER. The hub is the raised ground section between the bore and recess. It is the same width as the cutter. Collar spacers butt adjacent to the hub for holding and spacing of the cutter on the arbor. The hub diameter dimension is required to determine the allowable depth or cut and clearance between cutter and workpiece.
아래 그림 (A)와 (B)에서와 같이 출처에 따라 같은 명칭인 1번 여유각(1st clearance angle, primary clearance)과 2번 여유각(2nd clearance angle, secondary clearance)의 위치가 다를 수 있으므로 해당 문구에서 전후 사정으로 위치를 파악하기 바란다. 그림 (A)에는 1번 여유각이 relief angle이고 그림 (B)에서는 1번 여유각(primary angle)이 relief angle를 포함한다. 그림 (A)와 (B)에서 1번 여유각과 2번 여유각은 위치가 다르나, 우리의 관심사인 relief angle은 같은 곳의 각을 의미 하므로 혼돈 없기 바란다. 보통 여유각이라 하면 relief angle을 의미하며, 선반에서 relieving(cutting-off)은 relief angle(여유각)을 생기게 하는 것이며, cutter 축에 수직한 평면 내에서 land면과 절인의 법선 사이의 각으로서 cutter 절인의 밑면이 가공면을 문지르지 않도록 여유각(relief angle)을 두는 것이다.
(A) plain cutter	(B) plain cutter