The shell type straight machine reamers with centesimal progression, DIN 219 / UNI 6855, made of HSSE steel, 1/30 taper bore fitting and 6° left-hand spiral form B, are precision cutting tools designed for finishing, sizing and dimensional correction of existing holes on conventional and CNC machine tools. They are used when a hole must be brought to its final size with high accuracy, good roundness, controlled surface finish and consistent dimensional repeatability.

The main feature of these reamers is the shell type construction. Unlike reamers with an integral shank, a shell reamer is mounted on a dedicated arbor or toolholder through a 1/30 taper bore fitting. This solution allows the same support system to be used with different reamer diameters, making the tooling more modular and suitable for production, maintenance and setup operations where flexibility in size selection is required.

A reamer is not intended to create the hole, but to finish it after drilling, boring or rough machining. It removes a small and controlled amount of material from the internal diameter, improving the geometric quality of the seat and correcting minor irregularities left by the previous tool. The result is a more accurate hole, with improved cylindricity, better surface finish and higher dimensional consistency.

The centesimal progression is a key advantage when the hole must meet very precise dimensional requirements. Diameter availability in hundredth increments allows the most suitable size to be selected for the required fit, reducing the risk of excessive clearance, unwanted interference or non-conforming assemblies. This is especially useful for dowel pin seats, pins, bushes, guides, small shafts, centering components and mechanical parts intended for precision assembly.

The HSSE steel construction provides higher wear resistance than standard HSS and ensures good cutting edge stability in professional machining operations. It is suitable for steels, alloys, cast irons, ferrous and non-ferrous materials, depending on the machine, coolant, stock allowance and cutting parameters. HSSE is a suitable choice when tool life, reliability and constant precision are required in hole finishing.

The 6° left-hand spiral flutes, form B, support stable and controlled cutting. The left-hand spiral helps limit the tendency of the tool to self-feed into the hole and contributes to smoother machining behavior. Form B is suitable for reaming operations where cutting control, good surface finish, geometric accuracy and predictable tool behavior during feed are required.

For correct results, the hole must be prepared with a suitable stock allowance. If the pre-hole is too small, the reamer must remove too much material, increasing cutting force, heat, wear and risk of sticking. If the pre-hole is too close to the final size, the tool may not cut uniformly over the full surface, leaving geometric errors or uneven finish. Correct hole preparation is therefore essential for obtaining an accurate and repeatable seat.

The 1/30 taper bore fitting must be clean, undamaged and correctly matched with the arbor or support being used. Chips, dirt, dents or residues on the taper surface can compromise concentricity, rigidity and final accuracy. Before mounting, it is advisable to check both the reamer taper bore and the toolholder taper, ensuring that the coupling is stable and free from abnormal play.

During use, a stable machine, constant feed, suitable lubrication and accurate alignment between tool and hole are essential. The rigidity of the machine-toolholder-workpiece system is decisive for avoiding vibration, ovality, taper, scoring or dimensional errors. Reverse rotation while the reamer is inside the hole should also be avoided, as it may damage the cutting edges and compromise the quality of the machined surface.

These reamers are used in precision machine shops, CNC departments, machine building, industrial maintenance, automotive, toolrooms and subcontract machining. They are particularly suitable for finishing calibrated holes, cylindrical seats, holes for dowel pins, pins, bushes, guides, centering components and parts where hole accuracy directly affects assembly performance.

The HSSE shell type straight machine reamers with centesimal progression are a professional solution for producing accurate, calibrated and repeatable holes with a modular tooling system. The combination of shell type construction, 1/30 taper bore fitting, HSSE steel, 6° left-hand spiral form B and centesimal progression enables reliable machining on conventional and CNC machine tools, improving dimensional control, hole quality and productivity.