To improve the inner surface of the holes in accordance with the quality requirements of the used tool with multiple cutting edges – scan.
Holes in metal workpieces which are being finalized scan was obtained using drilling, boring cutters or countersinking. Achieve deployment of 6 to 9 precision quality class and surface roughness not more than 0,32-1,25 µm. Such a high quality is achievable due to the fact that unlike the cutter or drill bit, reamer has an increased number of cutting edges, which are cut more thin layer of metal from the blank from a few hundredths of a millimeter.
a Reamer is a rod in the form of a cylinder, consisting of a working part with cutting planes and smooth part of the shank square and bevel serving to secure the tool in the machining process. The working part, in turn, consists of several parts with differing geometries. A small area in the front is sharpened by the cone, and then cutting or the receiving period, after it is the guide cylindrical section. The last working part of the sweep cut back in the idea of the reverse cone. The cutting process occurs while applying translational and rotational motions, similar to drilling or reaming.
Scan produced with straight cutting edges or helical. Helical scan in the left-hand version is used when running in the clockwise direction, on the right when the rotation is counterclockwise. If it is wrong to choose the type of spiral, the scan is tightened in the hole. The machine can pop out of the machine spindle, as the possible breakdown of the shank and the attachment. Manual will experience heavy loads during operation and jam. Anyway, for all helical scan is characterized by high effort during the cutting process. It is advisable to apply them, subject to the availability in the bore of the cuts or grooves, which fall teeth sweep. The beginning and the end of the cutting of the spiral will be located on the required length on both sides of the recess in the tool with sufficient amount of tilt of the helix. The value of the tangent of this angle must be greater than the ratio of twice the width of the notch in the length of the processed holes.
Because of the uneven action of forces on each spiral in the radial direction on the surface of the hole can be formed by small grooves, alternating with ridges, which should not be quality parts. When you reprocess all these defects remain, since the position of the teeth relative to each other at the same distance will not change. The only way out is change the geometry of the helices, the location of their uneven. Upon rotation of the spiral every turnover will go to a new place, the edges of the hole. To avoid complex measurements during control of the tool, it is better to have cutting edges opposite in pairs, but through a different distance.
So the scan is always made with an even number of teeth, spaced unevenly along the arc measuring 180 degrees, the subsequent arc of 180 degrees similar to the first. Grooves upon receipt of the scan are cut corners (with an angle of teeth 80-85 degrees), or shaped krivozerye by mills. The height of the groove is usually equal to 0.20-0.28 pitch of the spirals, and the occipital groove angle is equal to 5-6 degrees. The width of the chamfer may have a value of 0.1 mm when the tool diameter is 3-7 millimeters to 0.30 millimeters in diameter more than 100 millimetres. Also, depending on the diameter and design the number of teeth is different. Form the cutting portion is rounded with a radius of 1 mm for a diameter scan 3-5 mm; 1.5 mm to 5-8 mm; 2,0 – for 8-14 mm and the tool diameter more than 14 mm the radius of curvature is taken to be 2.5 mm. The rounded shape suggests difficulties in sharpening and manufacture of the scanner. More simple configuration is a hollow beveled chamfer of the cutting portion.
Its length should be sufficient, since most of the work during cutting will be executed in this segment. The angle of inclination of the cutting when machining cast-iron workpieces on machine – 4-5 degrees, and the machining of iron and steel – 10-12 degrees. Length of cutting area for hand tools, much more, about one-fourth of the entire length of the sweep. For example, when the diameter of 3-6 mm, its value of 12.5 millimeters plus three-tenths of the diameter, and the diameter 27 millimeters – 25 millimeters plus six tenths of the diameter of the tool. For removing metal where the holes where allowance on deployment may be a bit more acceptable, uses a short front part in the form of a cone with an angle of 45-50 degrees. That is, first, there is a draft, and then finish the deployment. Half of the teeth in the scan system May processed in accordance with the finishing allowance, the second half has a short initial phase and performs a rough deployment.
the Transition of the cutting and guiding of the cylindrical parts is not sharp, otchitalsya abrasive tool. The length of the guide cut hand reamers are much more than machinery, or about three times. The magnitude of the reverse cone at the rear of the manual scans smaller (0,000125), machine – 0,001–0,003, and for tools operating in a turret machine, this value is multiplied by 2 or 3.
All scanner are divided into manual and machine type work. Tool design can be of several types – shell, adjustable, Gisholt (pritertymi teeth), permanent (common) and the surge in manual and machine performance. Form scan can be cylindrical or conical. Openings with a knob to get manual scans with a diameter of from 3 to 50 mm. For removing large allowances manually used the tool with a front section on which there is screw-thread. It contributes to a more accurate and smooth flow sweep.
For manual deployment through holes is used an expansion reamer having a conical screw. Most of the work is the middle part of the tool. Progressive scan – a more advanced tool. But it is also used for through holes or deaf, provided that they are not changing the diameter along the entire length of the hole. For this scan characteristic symmetrical shape, varying in diameter and an elongated front part in front of the cutting part. Conical screw 2 by 2 degrees to move the scan, the lock nuts are tightened plug-in blades made of tool steel (or high speed). The use of high-speed steel is not recommended as less resistant for small speeds and low temperature. Of cast open hearth steel get the body of the instrument.
Fixed scanner have a greater number of teeth than the adjustable. The range of diameters from 15 to 150 mm, number of teeth – 6-12. Teeth permanent hand and machine reamers are sharpened differently. Shank hand tools make a square, and that the machine is round or conical.
Scan after two or three shanks are reduced in diameter, and reduces the machining accuracy. So often the scans are preventie teeth (system Gisholt). They are periodically removed, put in their place a brass or a thick paper, thus increasing the diameter, and then grinding reaches the desired sweep.
Rarely used in the work expansion machine scans due to their low strength. Mainly used machine reamers with adjustable teeth, anchoring nuts for through holes and clamping straps or round dowels with tapered screws for blind holes.
There are also design scans with raznonaklonennymi teeth, improving the surface smoothness of the hole. Scan trailing cutters handle large holes.
Conical scan receive correspondingly tapered holes. If the hole is very large, first it rassverlivajut, and then expand set scan. After the passage of the first scan of a cylindrical stepped hole is formed. Rough passage and the second scan remove the corners. The third performs a finish machining.
a Small conical holes are deploying conical scans with a steeply slanted spiral, wherein the cut away a layer of metal is removed very easily. More perfect would be for this operation the combined tool bit plus conical scan, allowing complete operation in one pass. For the deployment of very small holes use five-sided tapered rod, called the scan system Stubs.
depending on workpiece material cutting speed range from the lowest 2-4 m/min for bronze up to 10-15 m/min on copper. Steel is 3-4 m/min when processing scan from tool steel and 4-5 m/min when cut with high speed steel tools. The feed rate will be smaller for harder materials.