Contents
Brief introduction of reamers
A reamer has a plurality of cutting edges, usually an even number, and is a rotary tool used to finish machined holes and remove thin layers of metal from the surface.
Reamers generally have straight or helical edges and are used to ream holes, which have high dimensional accuracy and good surface roughness.
Number of teeth, even pitch, uneven pitch
The number of teeth of the reamer is determined according to the size of its edge diameter, machining accuracy and the size of the chip space. Generally made into an even number, easy to measure its edge diameter. Reamer tooth spacing can be made equal or unequal. The purpose of the latter is to avoid periodic traces on the hole wall when reaming.
Helix angel
The helical angle of the reamer is generally made into a straight edge (0°). For reaming non–continuous surface of the hole or in order to further require the surface roughness of the reamed hole, can be designed into a spiral edge, which is divided into the left spiral and the right spiral which will affect the direction of chip removal.
Traight flute, right cutting
Most popular structure. Easy for re-grinding, more economic.
Left helix, right cutting
Better surface while worse cutting force for thinner allowance. Chips will be evacuated to the unmachined area for better surface. Not suitable for blind holes.
Right helix, right cutting
Surface grade worse than left helix, good cutting force, and suitable for thicker allowance. Chips will be evacuated to the machined area, leading to worse surface. Good for blind holes.
Rake angle
Due to the small amount of reaming allowance, reaming is only carried out at the tip area, and the rake surface of the teeth is rarely in contact, so the rake angle is generally designed for 0 degrees. It can also differ for the material to be processed. The following examples can be used as a reference:
Cast iron: 0°
Hardened steel: 0°~ 3°
Soft steel, copper, aluminum alloys: 6°~ 8°
Alloy steel, stainless steel: 8°~ 10°
Heat-resistant steel, high-chromium invisible steel: 8°~ 10°
Hardened steel: -15°~ -5°
Land margin
The outer diameter of the corrected part of the reamer and its inverted cone outer surface should be left with an land margin, which is to facilitate the measurement of the reamer edge diameter and to maintain stability in the reaming process. The surface roughness level of the land margin should be lower than the surface roughness of the processed hole by 1~2 levels. The width of the land margin is generally designed to be 0.02~0.03 times the diameter of the reamer, and the size of the width will affect the dimensional accuracy of the reamed hole (reaming and shrinkage) and surface roughness.
Back taper
The back taper part avoids the friction between the reamer and the reamed surface. The value of back taper is generally set at 0.03~0.04/100mm (the difference between large diameter and small diameter), and can also be different for the reamed material.
The following examples can be used as reference.
Reaming bronze, brass, cast iron, aluminum alloy and other light alloys: for 0.03 ~ 0.05/100 mm.
Soft steel, hard steel: for 0.05 ~ 0.07/100 mm.
Alloy steel, stainless steel: 0.07~0.10/100mm.
Heat–resistant steel, high chromium stainless steel: 0.1~0.25/100mm.
Leading chamfer
In order to make it easier for the reamer to reach into the hole, the front end of the reamer is usually ground with an chamfer with angle of 45°, while for high alloy steel and hardened steel, with an leading angle of 25°~30°.