Mill Tools

Anatomy of an Endmill

There is a lot of detail involved in endmill anatomy, as seen in the diagram below. Not all are needed in order to properly select a tool, so won’t worry about each minor detail in the diagram.

Flutes - These are the cutters on the endmill. Typically, 2 and 3 flute endmills are used for aluminum and other non-ferrous metals, while 4 flute endmills are used for steels and other harder materials.

Length of Cut - The length the endmill is able to cut. This is not equivalent to flute length.

Neck - This is the portion of the endmill that can rub on the material as the flutes cut during a deep cutting operation. It includes both the top portions of the flutes not suitable for cutting. A necked endmill has a portion of the length above the flutes at a smaller diameter to give it a deeper reach. Necked endmills aren’t the typical style, but they are an option if required.

Shank - Also known as the shoulder. This is the part of the endmill that is grabbed by the toolholder. It cannot cut and should never rub against material.

Coating & Material

Uncoated

Endmills for aluminum and other soft, nonferrous metals are typically uncoated. Some drill bits the team has purchased from McMaster are uncoated. The tool will have no difference in color from shank to cutter.

TiN (Titanium Nitride)

Drill bits and other general purpose tools are usually coated in TiN. They can be used in a variety of metals, but are typically used in ferrous ones. The cutter will be a yellow-gold color.

AlTiN (Aluminum Titanium Nitride)

Endmills meant for steels (both carbon and stainless), other ferrous metals, and high temperature alloys like Inconel are usually coated in AlTiN. The color will be a deep gray/black.

Standard Mill Tools

Square / Flat Endmill

Flat endmills have an extremely sharp corner, with a radius of around 0.002”. These corners wear easily, so they should not be used when roughing out a lot of material. They should be used when a better surface finish on the bottom is desired, or a sharp corner is needed.

Although they aren’t ideal for roughing due to the tool wear, these are the endmills that the capstone shop stocks. When working in there it is fine to use these for roughing.

Bullnose / Radiused Endmill

Bullnose endmills are the workhorse of endmills. They can take away material without much tool wear, while also leaving a flat and unscalloped bottom. They have a radius between that of a flat and ball endmill.

Typical radiuses that are used for roughing are 0.015-0.030”, however there are many options depending on the desired outcome.

Ball Endmill

Ball endmills are used where a smooth contour is desired with the cutting direction involving both up and down in the z-axis. It can also be used to give a large radius to an internal corner. The end radius is equal to the radius of the endmill itself.

Facemill

Facemills are a desirable option for facing. They result in very smooth finishes and take away a lot of material in stepover while not taking away very much in stepdown. They usually have a few cutting inserts that can be flipped or replaced when one gets damaged or worn down.

Specialty Mill Tools

Keyseat Cutters

Keyseat tools are used to undercut some material, where you want to create some sort of internal groove that a typical endmill could not. These are usually purchased on an application specific basis, as the cutter diameter ratio to the neck and the cutter length will likely need to be pretty specific. These are usually used to cut grooves for retaining rings.

Toolholding

ER-## Collets

These types of collets are the standard for toolholding in the MIE Capstone Shop. ER collets have slits on both their front and backside, which allows for a wider grip range than their 5C counterparts [see Collet Blocks in Mill Workholding]. The collets come in a few different external sizes shown by the two digit number in their name. ER-20 collets are sufficient for most jobs done in the MIE Capstone shop. If a tool with a shank diameter of >1/2” is needed, a larger collet such as an ER-32 might be used.

These collets are to be installed with a torque wrench. ER-20 holders usually take hex, and ER-32 holders usually take some sort of spanner.

Drill Chucks

Drill chucks for CNC are virtually the same as any other drill chuck. They have three jaws which cinch inward as tightened. They are tightened with a spanner wrench or chuck key by hand. They are meant for drills, so use them as such.