After pre-drilling and reboring, it is advisable to countersink the hole with a 60 ° countersink so that the reamer cuts better. Often the reamers cut at the front also has an angle of 60 °. Then the hole is brought to nominal size with the help of the reamer. In this way, smaller tolerances can be produced.
The achievable dimensional tolerance is normally IT7 . In special cases IT6 or even IT5 is also possible. With the degree of accuracy, higher accuracies in form and position tolerances are also maintained. Rubbing improves roundness and cylindricity .
A reamer is similar to a flute drill for metal. However, the cutting edges are located on the circumference, only in exceptional cases also on the gate. The cutting edges and flutes are either straight and accordingly run along the axis of the reamer (i.e. in a purely axial direction) or in a helical shape as in a spiral groove drill / twist drill.
For normal through holes, helical cutting edges with a left-hand pitch are ideal. Due to the incline to the left, the chips produced during reaming are carried away to the front, so that the surface of the hole is prevented from being scratched by chips caught between the wall of the hole and the cutting edge of the reamer. Right-hand pitch reamers (as in common twist drills ) are used for blind holes so that the chips are conveyed out of the bore. The reamers with helical flutes are particularly indispensable for friction with interrupted cuts.
Above all, reamers with an even number of teeth (because the diameter can be measured more easily) and uneven tooth pitch (which reduces chatter) have proven to be particularly effective. Typical diameters are between 1 mm and 50 mm. Adjustable reamers as a special form of the reamer are not intended for a specific fit, but can be set for the production of individual diameters.
Materials for reamers can be:
- High speed steel (HSS),
- Carbide , either made of solid carbide, with brazed carbide cutting edges on a steel body, or equipped with exchangeable indexable inserts
- Polycrystalline diamond
- Boron nitride
A distinction is also made between machine and hand reamers.
- For better guidance, hand reamers have a long lead of approx. 1/4 the length of the cutting edge and a longer guide part. At the end of the shaft there is a square for holding in a tap wrench .
- Machine reamers have a short lead and guide part, as they are guided by the machine spindle. Because of the short lead, machine reamers are better suited for short blind holes.
- Basics of reaming, reamers, shapes and application, cutting data. Pre-drilling diameter, table: dimensions achievable with reamers, fit table. https://www.hhw.de/uploads/schnittdaten/Grundlagen_Reiben.pdf
- Oskar Gönner: Reaming as the fine machining of bores in metallic materials . In: Expansion , Issue 4/1957 (pp. 210–217), Issue 5/1957 (pp. 266–272), Issue 6/1957 (pp. 358–368), Paul-Christiani-Verlag, Konstanz 1957