Multipurpose mills

For machining operations in which change is a constant, general-purpose endmills can have a value that far exceeds their actual cost. As the name suggests, these endmills are not designed for a specific cutting application or material. Instead, they are tools that can be used for most standard machining jobs.

“I see a general-purpose mill as the adjustable wrench of cutting tools,” said Dan Doiron, milling product manager at Emuge-Franken USA, a tool manufacturer in West Boylston, Massachusetts. “The adjustable wrench can adapt to many bolt sizes conveniently and quickly on the spot.”

Similarly, he said general-purpose endmills provide the versatility needed at shops where rush jobs often pop up and there is no time to determine whether the exact tool is available for each material that must be machined. For this reason, these endmills must be capable of machining most materials, from aluminum to hardened steels.

The V7 Plus offers good performance in a variety of materials. Image courtesy of YG-1 Tool (USA)

Designed for the requirements of fast-paced, fast-changing machining environments, Doiron said a general-purpose mill “will get you running quickly and efficiently without breaking the bank.”

Another Option

An alternative to a general-purpose endmill is a high-performance tool.

“If you have the right part with the right machine and the right program, a high-performance tool will work better than a general-purpose (one),” said Yair Bruhis, global industry project manager at YG-1 Tool (USA) Co. in Vernon Hills, Illinois.

Unlike general-purpose endmills, he said high-performance tools normally are aimed at specific applications. For example, a high-performance endmill might be designed to cut titanium in a high-speed machining application.

While a custom or special endmill is usually a high-performance tool, Bruhis pointed out that both general-purpose and high-performance endmills can be either off-the-shelf or custom tools. He noted that a custom high-performance tool sometimes is designed from scratch to meet the requirements of a particular application. But this normally wouldn’t be done to create a custom general-purpose tool.

“Usually,” he said, “you just modify a general-purpose and call it a special.”

Key Characteristics

Bruhis said those comparing the designs of typical general-purpose and high-performance endmills will notice significant differences in the flutes on the tools. For one thing, he said, general-purpose endmills normally have two to four flutes while high-performance tools probably will have at least five and possibly as many as 12 flutes. In addition, he noted that high-performance endmills have unequal index and variable helix angles to minimize vibration. So while all the flutes on general-purpose endmills will have helix angles of about 30 degrees, a high-performance tool might have a couple of flutes with 37-degree helix angles and a couple with 35-degree helix angles, he said.

An exception to this rule, however, is Emuge-Franken’s Top-Cut VAR. Billed as a multipurpose endmill, Doiron said Top-Cut VAR features flutes with variable helix angles that provide significant vibration dampening.

Other features that generally distinguish high-performance endmills from general-purpose alternatives include special coatings and edge preparation. When it comes to coatings, Bruhis said general-purpose endmills normally sport common coatings, such as AlTiN and TiCN, while high-performance tools might get a special coating like TiAlSiN or AlCrN.

Regarding size options, general-purpose endmills usually offer more than their high-performance counterparts. He said one of the biggest advantages of general-purpose endmills is that they come in diameters down to 0.396875 mm (1/64″) while high-performance tool diameters commonly go only as low as 3.175 mm (1/8″) or 6.35 mm (1/4″).

“So when you talk about very small tools,” Bruhis said, “you’re going to use general-purpose in most cases.”

Another major advantage of general-purpose endmills is their relatively low cost.

“For the small job-shop environment,” Doiron said, “it’s usually the cost of the tool that will direct their sights to the general-purpose mill.”

Bruhis said the prices of general-purpose endmills typically are 20% to 40% lower than high-performance tools. And Doiron noted that the versatility of general-purpose endmills saves money in another way because users need fewer endmill types in their toolcribs to handle a variety of jobs.

However, Bruhis sees more and more shops moving from general-purpose to high-performance endmills because the price of tooling is only 3% to 5% of the overall manufacturing cost, as well as the dropping price of some high-performance tools. As an example, he points to demand for YG-1 Tool’s V7 Plus endmill.