Tooling for Machining Centers

CNC Applications

Cutting Tools

Most machining centers use some form of HSS or carbide insert endmillas the basic cutting tool.

Insert endmills cut many times faster than HSS, but the HSS endmills leave a better finish when side cutting.Photo courtesy ISCAR.

Cutting Tools (continued)

Facemills flatten large surfaces quickly and with an excellent finish. Notice the engine block being finished in one pass with a large cutter.Photo courtesy ISCAR.

Cutting Tools (continued)

Ball endmills (both HSS and insert) are used for a variety of profiling operations such as the mold shown in the picture.

Slitting and side cutters are used when deep, narrow slots must be cut.Photos courtesy ISCAR.

Milling Feed Direction

Remember, all CNC machines are equipped with ball screws to minimize slop when changing feed directions. The other advantage to ball screws is they allow climb milling instead of conventional milling as done on most manual machines.

Climb milling has many advantages including better surface finish, longer tool life, and the cutter deflects away from the work rather than into it.

Always climb mill on a CNC machining center!

Drills, Taps, and Reamers

Common HSS tools such as drills, taps, and reamers are commonly used on CNC machining centers. Note that a spot drill is used instead of a centerdrill. Also, spiral point or gun taps are used for through holes and spiral flute for blind holes. Rarely are hand taps used on a machining center.Drawings courtesy Precision Twist Drill.

Tool HoldersAll cutting tools must be held in a holder that fits in the spindle. These include end mill holders (shown), collet holders, face mill adapters, etc.

Most machines in the USA use a CAT taper which is a modified NST 30, 40, or 50 taper that uses a pull stud and a groove in the flange. The machine pulls on the pull stud to hold the holder in the spindle, and the groove in the flange gives the automatictool changer something to hold onto.

HSK tool holders were designed a number of years ago as an improvement to CAT tapers, but they are gaining acceptance slowly.Photo courtesy Fitz-Rite

The gage length shown in the drawing is entered in the machine control as the tool length. The machine then compensates for the length.

Fixtures

Fixtures include anything that holds the work on the machining center table.

Holding parts on a machining center tends to be much more difficult than on a turning center.

The simplest fixture is just a vise as shown in the top photo.

The next photo shows a double vise with machinable jaws to hold odd shaped pieces.

The tombstone shown in the lower photo has a double vise on each face for use on a four or five axis machining center.Photos courtesy Kurt Manufacturing.

More Fixtures

When parts can’t be held in a vise, a custom fixture must be used. Fixtures for high production parts are often custom designed and manufactured at great expense.

For small runs of odd-shaped parts, many manufacturers have turned to modular fixturing. As shown in the upper drawing, modular fixturing consists of many precision ground pieces that fit together to hold all sorts of parts as shown in the lower photo.Drawing and photo courtesy Bluco.