Q&A on the Multi-Master Line of Milling Tools with Interchangeable Solid-carbide Heads

Iscar: introduced the Multi-Master family of rotating cutting tools with interchangeable solid-carbide heads in 2000. These tools now have a strong presence in the manufacturing industry and are widely accepted by metalworking specialists. To explain the line’s capabilities, Iscar has prepared an informative question-and-answer session.

The Multi-Master design features a solid-carbide head connected with the tool body (shank) via a specially shaped thread. The thread connection, being successfully produced directly on a solid-carbide part, changed preexisting views regarding such an approach and motivated other cutting-tool producers to create similar systems.

In Multi-Master, one shank can carry heads of various cutting shapes. This maximizes the family’s versatility and functionality, significantly decreases the need for specially tailored tools, and enables users to reduce tool inventory. A few combinations of Multi-Master heads and shanks produce a great variety of cutting tools that meet exacting performance requirements and ensure reductions in production and logistical costs. Unlike with regular solid tools, regrinding is unnecessary, and tungsten carbide consumption is lessened.

The following Q&A presents questions new Multi-Master users typically ask, with answers that make clear the technological advantages this tool family offers.

How is a head mounted into a shank? A head has two surfaces: a short taper and a rear noncutting face that determines the head location in a shank. The taper ensures high concentricity, and the face a face contact. The thread is intended for securing the head. Therefore the rear (tail) part of the head has two areas: tapered and threaded.

During mounting, the head is initially rotated by hand and then tightened by means of a key. The head has flats for applying a key.

What are the advantages of the face contact? First, the face contact considerably increases both the stiffness of an assembled tool and its ability to withstand impact loading. This factor allows for stable cutting, minimizes vibrations and reduces power consumption.

Second, the face contact ensures high repeatability of the head overhang with respect to the shank. As a result, no additional adjustment is necessary after a head is replaced. An operator can change the head without removing the shank from a machine tool spindle.

What is meant by the “initial gap”? When tightening a head, an operator first rotates the head by hand. The head stops rotating at some point, and a small gap remains between the contact faces of the head and the shank. This important “initial” gap measures several tenths of a millimetre, the exact value depending on the thread size. Further head tightening is possible only with the use of the key. Tightening of the head causes elastic deformation, in a radial direction, of the contact area of the shank section.

Why is behind the Multi-Master thread’s special profile? Multi-Master heads are produced from tungsten carbide, an extremely hard heat-resistant material that exhibits lowered impact strength against certain workpiece materials, as, for example, high-speed steel (HSS). One of the main problems to be solved in designing a threaded tungsten carbide part thus is to minimize stress concentrators.

Additionally, the Multi-Master thread connection is relatively small, with nominal thread diameters generally between 5 and 15 mm. These sizes, along with the need to meet strength requirements for operational loads, can limit the height of the thread profile.

Therefore, using the standard threads would be problematic. A special thread shape that will comply with specifications of the connection was clearly necessary, and that is why Iscar designed the special-profile thread, which is called the T-thread.

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